merge 3.2

This commit is contained in:
Benjamin Peterson 2012-10-12 12:04:32 -04:00
commit 143d034ecd
14 changed files with 242 additions and 240 deletions

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@ -365,7 +365,7 @@ Glossary
iterator iterator
An object representing a stream of data. Repeated calls to the iterator's An object representing a stream of data. Repeated calls to the iterator's
:meth:`__next__` method (or passing it to the built-in function :meth:`~iterator.__next__` method (or passing it to the built-in function
:func:`next`) return successive items in the stream. When no more data :func:`next`) return successive items in the stream. When no more data
are available a :exc:`StopIteration` exception is raised instead. At this are available a :exc:`StopIteration` exception is raised instead. At this
point, the iterator object is exhausted and any further calls to its point, the iterator object is exhausted and any further calls to its

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@ -181,26 +181,26 @@ foundation for writing functional-style programs: iterators.
An iterator is an object representing a stream of data; this object returns the An iterator is an object representing a stream of data; this object returns the
data one element at a time. A Python iterator must support a method called data one element at a time. A Python iterator must support a method called
``__next__()`` that takes no arguments and always returns the next element of :meth:`~iterator.__next__` that takes no arguments and always returns the next
the stream. If there are no more elements in the stream, ``__next__()`` must element of the stream. If there are no more elements in the stream,
raise the ``StopIteration`` exception. Iterators don't have to be finite, :meth:`~iterator.__next__` must raise the :exc:`StopIteration` exception.
though; it's perfectly reasonable to write an iterator that produces an infinite Iterators don't have to be finite, though; it's perfectly reasonable to write
stream of data. an iterator that produces an infinite stream of data.
The built-in :func:`iter` function takes an arbitrary object and tries to return The built-in :func:`iter` function takes an arbitrary object and tries to return
an iterator that will return the object's contents or elements, raising an iterator that will return the object's contents or elements, raising
:exc:`TypeError` if the object doesn't support iteration. Several of Python's :exc:`TypeError` if the object doesn't support iteration. Several of Python's
built-in data types support iteration, the most common being lists and built-in data types support iteration, the most common being lists and
dictionaries. An object is called an **iterable** object if you can get an dictionaries. An object is called :term:`iterable` if you can get an iterator
iterator for it. for it.
You can experiment with the iteration interface manually: You can experiment with the iteration interface manually:
>>> L = [1,2,3] >>> L = [1,2,3]
>>> it = iter(L) >>> it = iter(L)
>>> it >>> it #doctest: +ELLIPSIS
<...iterator object at ...> <...iterator object at ...>
>>> it.__next__() >>> it.__next__() # same as next(it)
1 1
>>> next(it) >>> next(it)
2 2
@ -213,9 +213,9 @@ You can experiment with the iteration interface manually:
>>> >>>
Python expects iterable objects in several different contexts, the most Python expects iterable objects in several different contexts, the most
important being the ``for`` statement. In the statement ``for X in Y``, Y must important being the :keyword:`for` statement. In the statement ``for X in Y``,
be an iterator or some object for which ``iter()`` can create an iterator. Y must be an iterator or some object for which :func:`iter` can create an
These two statements are equivalent:: iterator. These two statements are equivalent::
for i in iter(obj): for i in iter(obj):
@ -246,16 +246,16 @@ Built-in functions such as :func:`max` and :func:`min` can take a single
iterator argument and will return the largest or smallest element. The ``"in"`` iterator argument and will return the largest or smallest element. The ``"in"``
and ``"not in"`` operators also support iterators: ``X in iterator`` is true if and ``"not in"`` operators also support iterators: ``X in iterator`` is true if
X is found in the stream returned by the iterator. You'll run into obvious X is found in the stream returned by the iterator. You'll run into obvious
problems if the iterator is infinite; ``max()``, ``min()`` problems if the iterator is infinite; :func:`max`, :func:`min`
will never return, and if the element X never appears in the stream, the will never return, and if the element X never appears in the stream, the
``"in"`` and ``"not in"`` operators won't return either. ``"in"`` and ``"not in"`` operators won't return either.
Note that you can only go forward in an iterator; there's no way to get the Note that you can only go forward in an iterator; there's no way to get the
previous element, reset the iterator, or make a copy of it. Iterator objects previous element, reset the iterator, or make a copy of it. Iterator objects
can optionally provide these additional capabilities, but the iterator protocol can optionally provide these additional capabilities, but the iterator protocol
only specifies the ``next()`` method. Functions may therefore consume all of only specifies the :meth:`~iterator.__next__` method. Functions may therefore
the iterator's output, and if you need to do something different with the same consume all of the iterator's output, and if you need to do something different
stream, you'll have to create a new iterator. with the same stream, you'll have to create a new iterator.
@ -267,15 +267,11 @@ sequence type, such as strings, will automatically support creation of an
iterator. iterator.
Calling :func:`iter` on a dictionary returns an iterator that will loop over the Calling :func:`iter` on a dictionary returns an iterator that will loop over the
dictionary's keys: dictionary's keys::
.. not a doctest since dict ordering varies across Pythons
::
>>> m = {'Jan': 1, 'Feb': 2, 'Mar': 3, 'Apr': 4, 'May': 5, 'Jun': 6, >>> m = {'Jan': 1, 'Feb': 2, 'Mar': 3, 'Apr': 4, 'May': 5, 'Jun': 6,
... 'Jul': 7, 'Aug': 8, 'Sep': 9, 'Oct': 10, 'Nov': 11, 'Dec': 12} ... 'Jul': 7, 'Aug': 8, 'Sep': 9, 'Oct': 10, 'Nov': 11, 'Dec': 12}
>>> for key in m: >>> for key in m: #doctest: +SKIP
... print(key, m[key]) ... print(key, m[key])
Mar 3 Mar 3
Feb 2 Feb 2
@ -296,7 +292,7 @@ ordering of the objects in the dictionary.
Applying :func:`iter` to a dictionary always loops over the keys, but Applying :func:`iter` to a dictionary always loops over the keys, but
dictionaries have methods that return other iterators. If you want to iterate dictionaries have methods that return other iterators. If you want to iterate
over values or key/value pairs, you can explicitly call the over values or key/value pairs, you can explicitly call the
:meth:`values` or :meth:`items` methods to get an appropriate iterator. :meth:`~dict.values` or :meth:`~dict.items` methods to get an appropriate iterator.
The :func:`dict` constructor can accept an iterator that returns a finite stream The :func:`dict` constructor can accept an iterator that returns a finite stream
of ``(key, value)`` tuples: of ``(key, value)`` tuples:
@ -305,9 +301,9 @@ of ``(key, value)`` tuples:
>>> dict(iter(L)) >>> dict(iter(L))
{'Italy': 'Rome', 'US': 'Washington DC', 'France': 'Paris'} {'Italy': 'Rome', 'US': 'Washington DC', 'France': 'Paris'}
Files also support iteration by calling the ``readline()`` method until there Files also support iteration by calling the :meth:`~io.TextIOBase.readline`
are no more lines in the file. This means you can read each line of a file like method until there are no more lines in the file. This means you can read each
this:: line of a file like this::
for line in file: for line in file:
# do something for each line # do something for each line
@ -410,12 +406,9 @@ clauses, the length of the resulting output will be equal to the product of the
lengths of all the sequences. If you have two lists of length 3, the output lengths of all the sequences. If you have two lists of length 3, the output
list is 9 elements long: list is 9 elements long:
.. doctest::
:options: +NORMALIZE_WHITESPACE
>>> seq1 = 'abc' >>> seq1 = 'abc'
>>> seq2 = (1,2,3) >>> seq2 = (1,2,3)
>>> [(x,y) for x in seq1 for y in seq2] >>> [(x, y) for x in seq1 for y in seq2] #doctest: +NORMALIZE_WHITESPACE
[('a', 1), ('a', 2), ('a', 3), [('a', 1), ('a', 2), ('a', 3),
('b', 1), ('b', 2), ('b', 3), ('b', 1), ('b', 2), ('b', 3),
('c', 1), ('c', 2), ('c', 3)] ('c', 1), ('c', 2), ('c', 3)]
@ -425,9 +418,9 @@ creating a tuple, it must be surrounded with parentheses. The first list
comprehension below is a syntax error, while the second one is correct:: comprehension below is a syntax error, while the second one is correct::
# Syntax error # Syntax error
[ x,y for x in seq1 for y in seq2] [x, y for x in seq1 for y in seq2]
# Correct # Correct
[ (x,y) for x in seq1 for y in seq2] [(x, y) for x in seq1 for y in seq2]
Generators Generators
@ -448,15 +441,13 @@ is what generators provide; they can be thought of as resumable functions.
Here's the simplest example of a generator function: Here's the simplest example of a generator function:
.. testcode:: >>> def generate_ints(N):
... for i in range(N):
... yield i
def generate_ints(N): Any function containing a :keyword:`yield` keyword is a generator function;
for i in range(N): this is detected by Python's :term:`bytecode` compiler which compiles the
yield i function specially as a result.
Any function containing a ``yield`` keyword is a generator function; this is
detected by Python's :term:`bytecode` compiler which compiles the function
specially as a result.
When you call a generator function, it doesn't return a single value; instead it When you call a generator function, it doesn't return a single value; instead it
returns a generator object that supports the iterator protocol. On executing returns a generator object that supports the iterator protocol. On executing
@ -464,12 +455,13 @@ the ``yield`` expression, the generator outputs the value of ``i``, similar to a
``return`` statement. The big difference between ``yield`` and a ``return`` ``return`` statement. The big difference between ``yield`` and a ``return``
statement is that on reaching a ``yield`` the generator's state of execution is statement is that on reaching a ``yield`` the generator's state of execution is
suspended and local variables are preserved. On the next call to the suspended and local variables are preserved. On the next call to the
generator's ``.__next__()`` method, the function will resume executing. generator's :meth:`~generator.__next__` method, the function will resume
executing.
Here's a sample usage of the ``generate_ints()`` generator: Here's a sample usage of the ``generate_ints()`` generator:
>>> gen = generate_ints(3) >>> gen = generate_ints(3)
>>> gen >>> gen #doctest: +ELLIPSIS
<generator object generate_ints at ...> <generator object generate_ints at ...>
>>> next(gen) >>> next(gen)
0 0
@ -491,17 +483,19 @@ value, and signals the end of the procession of values; after executing a
``return`` the generator cannot return any further values. ``return`` with a ``return`` the generator cannot return any further values. ``return`` with a
value, such as ``return 5``, is a syntax error inside a generator function. The value, such as ``return 5``, is a syntax error inside a generator function. The
end of the generator's results can also be indicated by raising end of the generator's results can also be indicated by raising
``StopIteration`` manually, or by just letting the flow of execution fall off :exc:`StopIteration` manually, or by just letting the flow of execution fall off
the bottom of the function. the bottom of the function.
You could achieve the effect of generators manually by writing your own class You could achieve the effect of generators manually by writing your own class
and storing all the local variables of the generator as instance variables. For and storing all the local variables of the generator as instance variables. For
example, returning a list of integers could be done by setting ``self.count`` to example, returning a list of integers could be done by setting ``self.count`` to
0, and having the ``__next__()`` method increment ``self.count`` and return it. 0, and having the :meth:`~iterator.__next__` method increment ``self.count`` and
return it.
However, for a moderately complicated generator, writing a corresponding class However, for a moderately complicated generator, writing a corresponding class
can be much messier. can be much messier.
The test suite included with Python's library, ``test_generators.py``, contains The test suite included with Python's library,
:source:`Lib/test/test_generators.py`, contains
a number of more interesting examples. Here's one generator that implements an a number of more interesting examples. Here's one generator that implements an
in-order traversal of a tree using generators recursively. :: in-order traversal of a tree using generators recursively. ::
@ -544,23 +538,23 @@ when you're doing something with the returned value, as in the above example.
The parentheses aren't always necessary, but it's easier to always add them The parentheses aren't always necessary, but it's easier to always add them
instead of having to remember when they're needed. instead of having to remember when they're needed.
(PEP 342 explains the exact rules, which are that a ``yield``-expression must (:pep:`342` explains the exact rules, which are that a ``yield``-expression must
always be parenthesized except when it occurs at the top-level expression on the always be parenthesized except when it occurs at the top-level expression on the
right-hand side of an assignment. This means you can write ``val = yield i`` right-hand side of an assignment. This means you can write ``val = yield i``
but have to use parentheses when there's an operation, as in ``val = (yield i) but have to use parentheses when there's an operation, as in ``val = (yield i)
+ 12``.) + 12``.)
Values are sent into a generator by calling its ``send(value)`` method. This Values are sent into a generator by calling its :meth:`send(value)
method resumes the generator's code and the ``yield`` expression returns the <generator.send>` method. This method resumes the generator's code and the
specified value. If the regular ``__next__()`` method is called, the ``yield`` ``yield`` expression returns the specified value. If the regular
returns ``None``. :meth:`~generator.__next__` method is called, the ``yield`` returns ``None``.
Here's a simple counter that increments by 1 and allows changing the value of Here's a simple counter that increments by 1 and allows changing the value of
the internal counter. the internal counter.
.. testcode:: .. testcode::
def counter (maximum): def counter(maximum):
i = 0 i = 0
while i < maximum: while i < maximum:
val = (yield i) val = (yield i)
@ -572,16 +566,16 @@ the internal counter.
And here's an example of changing the counter: And here's an example of changing the counter:
>>> it = counter(10) >>> it = counter(10) #doctest: +SKIP
>>> next(it) >>> next(it) #doctest: +SKIP
0 0
>>> next(it) >>> next(it) #doctest: +SKIP
1 1
>>> it.send(8) >>> it.send(8) #doctest: +SKIP
8 8
>>> next(it) >>> next(it) #doctest: +SKIP
9 9
>>> next(it) >>> next(it) #doctest: +SKIP
Traceback (most recent call last): Traceback (most recent call last):
File "t.py", line 15, in ? File "t.py", line 15, in ?
it.next() it.next()
@ -589,20 +583,23 @@ And here's an example of changing the counter:
Because ``yield`` will often be returning ``None``, you should always check for Because ``yield`` will often be returning ``None``, you should always check for
this case. Don't just use its value in expressions unless you're sure that the this case. Don't just use its value in expressions unless you're sure that the
``send()`` method will be the only method used resume your generator function. :meth:`~generator.send` method will be the only method used resume your
generator function.
In addition to ``send()``, there are two other new methods on generators: In addition to :meth:`~generator.send`, there are two other methods on
generators:
* ``throw(type, value=None, traceback=None)`` is used to raise an exception * :meth:`throw(type, value=None, traceback=None) <generator.throw>` is used to
inside the generator; the exception is raised by the ``yield`` expression raise an exception inside the generator; the exception is raised by the
where the generator's execution is paused. ``yield`` expression where the generator's execution is paused.
* ``close()`` raises a :exc:`GeneratorExit` exception inside the generator to * :meth:`~generator.close` raises a :exc:`GeneratorExit` exception inside the
terminate the iteration. On receiving this exception, the generator's code generator to terminate the iteration. On receiving this exception, the
must either raise :exc:`GeneratorExit` or :exc:`StopIteration`; catching the generator's code must either raise :exc:`GeneratorExit` or
exception and doing anything else is illegal and will trigger a :exc:`StopIteration`; catching the exception and doing anything else is
:exc:`RuntimeError`. ``close()`` will also be called by Python's garbage illegal and will trigger a :exc:`RuntimeError`. :meth:`~generator.close`
collector when the generator is garbage-collected. will also be called by Python's garbage collector when the generator is
garbage-collected.
If you need to run cleanup code when a :exc:`GeneratorExit` occurs, I suggest If you need to run cleanup code when a :exc:`GeneratorExit` occurs, I suggest
using a ``try: ... finally:`` suite instead of catching :exc:`GeneratorExit`. using a ``try: ... finally:`` suite instead of catching :exc:`GeneratorExit`.
@ -624,13 +621,12 @@ Let's look in more detail at built-in functions often used with iterators.
Two of Python's built-in functions, :func:`map` and :func:`filter` duplicate the Two of Python's built-in functions, :func:`map` and :func:`filter` duplicate the
features of generator expressions: features of generator expressions:
``map(f, iterA, iterB, ...)`` returns an iterator over the sequence :func:`map(f, iterA, iterB, ...) <map>` returns an iterator over the sequence
``f(iterA[0], iterB[0]), f(iterA[1], iterB[1]), f(iterA[2], iterB[2]), ...``. ``f(iterA[0], iterB[0]), f(iterA[1], iterB[1]), f(iterA[2], iterB[2]), ...``.
>>> def upper(s): >>> def upper(s):
... return s.upper() ... return s.upper()
>>> list(map(upper, ['sentence', 'fragment'])) >>> list(map(upper, ['sentence', 'fragment']))
['SENTENCE', 'FRAGMENT'] ['SENTENCE', 'FRAGMENT']
>>> [upper(s) for s in ['sentence', 'fragment']] >>> [upper(s) for s in ['sentence', 'fragment']]
@ -638,11 +634,11 @@ features of generator expressions:
You can of course achieve the same effect with a list comprehension. You can of course achieve the same effect with a list comprehension.
``filter(predicate, iter)`` returns an iterator over all the sequence elements :func:`filter(predicate, iter) <filter>` returns an iterator over all the
that meet a certain condition, and is similarly duplicated by list sequence elements that meet a certain condition, and is similarly duplicated by
comprehensions. A **predicate** is a function that returns the truth value of list comprehensions. A **predicate** is a function that returns the truth
some condition; for use with :func:`filter`, the predicate must take a single value of some condition; for use with :func:`filter`, the predicate must take a
value. single value.
>>> def is_even(x): >>> def is_even(x):
... return (x % 2) == 0 ... return (x % 2) == 0
@ -657,8 +653,8 @@ This can also be written as a list comprehension:
[0, 2, 4, 6, 8] [0, 2, 4, 6, 8]
``enumerate(iter)`` counts off the elements in the iterable, returning 2-tuples :func:`enumerate(iter) <enumerate>` counts off the elements in the iterable,
containing the count and each element. :: returning 2-tuples containing the count and each element. ::
>>> for item in enumerate(['subject', 'verb', 'object']): >>> for item in enumerate(['subject', 'verb', 'object']):
... print(item) ... print(item)
@ -674,29 +670,28 @@ indexes at which certain conditions are met::
if line.strip() == '': if line.strip() == '':
print('Blank line at line #%i' % i) print('Blank line at line #%i' % i)
``sorted(iterable, [key=None], [reverse=False])`` collects all the elements of :func:`sorted(iterable, key=None, reverse=False) <sorted>` collects all the
the iterable into a list, sorts the list, and returns the sorted result. The elements of the iterable into a list, sorts the list, and returns the sorted
``key``, and ``reverse`` arguments are passed through to the constructed list's result. The *key*, and *reverse* arguments are passed through to the
``.sort()`` method. :: constructed list's :meth:`~list.sort` method. ::
>>> import random >>> import random
>>> # Generate 8 random numbers between [0, 10000) >>> # Generate 8 random numbers between [0, 10000)
>>> rand_list = random.sample(range(10000), 8) >>> rand_list = random.sample(range(10000), 8)
>>> rand_list >>> rand_list #doctest: +SKIP
[769, 7953, 9828, 6431, 8442, 9878, 6213, 2207] [769, 7953, 9828, 6431, 8442, 9878, 6213, 2207]
>>> sorted(rand_list) >>> sorted(rand_list) #doctest: +SKIP
[769, 2207, 6213, 6431, 7953, 8442, 9828, 9878] [769, 2207, 6213, 6431, 7953, 8442, 9828, 9878]
>>> sorted(rand_list, reverse=True) >>> sorted(rand_list, reverse=True) #doctest: +SKIP
[9878, 9828, 8442, 7953, 6431, 6213, 2207, 769] [9878, 9828, 8442, 7953, 6431, 6213, 2207, 769]
(For a more detailed discussion of sorting, see the Sorting mini-HOWTO in the (For a more detailed discussion of sorting, see the :ref:`sortinghowto`.)
Python wiki at http://wiki.python.org/moin/HowTo/Sorting.)
The ``any(iter)`` and ``all(iter)`` built-ins look at the truth values of an The :func:`any(iter) <any>` and :func:`all(iter) <all>` built-ins look at the
iterable's contents. :func:`any` returns True if any element in the iterable is truth values of an iterable's contents. :func:`any` returns True if any element
a true value, and :func:`all` returns True if all of the elements are true in the iterable is a true value, and :func:`all` returns True if all of the
values: elements are true values:
>>> any([0,1,0]) >>> any([0,1,0])
True True
@ -712,7 +707,7 @@ values:
True True
``zip(iterA, iterB, ...)`` takes one element from each iterable and :func:`zip(iterA, iterB, ...) <zip>` takes one element from each iterable and
returns them in a tuple:: returns them in a tuple::
zip(['a', 'b', 'c'], (1, 2, 3)) => zip(['a', 'b', 'c'], (1, 2, 3)) =>
@ -752,42 +747,44 @@ The module's functions fall into a few broad classes:
Creating new iterators Creating new iterators
---------------------- ----------------------
``itertools.count(n)`` returns an infinite stream of integers, increasing by 1 :func:`itertools.count(n) <itertools.count>` returns an infinite stream of
each time. You can optionally supply the starting number, which defaults to 0:: integers, increasing by 1 each time. You can optionally supply the starting
number, which defaults to 0::
itertools.count() => itertools.count() =>
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ... 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ...
itertools.count(10) => itertools.count(10) =>
10, 11, 12, 13, 14, 15, 16, 17, 18, 19, ... 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, ...
``itertools.cycle(iter)`` saves a copy of the contents of a provided iterable :func:`itertools.cycle(iter) <itertools.cycle>` saves a copy of the contents of
and returns a new iterator that returns its elements from first to last. The a provided iterable and returns a new iterator that returns its elements from
new iterator will repeat these elements infinitely. :: first to last. The new iterator will repeat these elements infinitely. ::
itertools.cycle([1,2,3,4,5]) => itertools.cycle([1,2,3,4,5]) =>
1, 2, 3, 4, 5, 1, 2, 3, 4, 5, ... 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, ...
``itertools.repeat(elem, [n])`` returns the provided element ``n`` times, or :func:`itertools.repeat(elem, [n]) <itertools.repeat>` returns the provided
returns the element endlessly if ``n`` is not provided. :: element *n* times, or returns the element endlessly if *n* is not provided. ::
itertools.repeat('abc') => itertools.repeat('abc') =>
abc, abc, abc, abc, abc, abc, abc, abc, abc, abc, ... abc, abc, abc, abc, abc, abc, abc, abc, abc, abc, ...
itertools.repeat('abc', 5) => itertools.repeat('abc', 5) =>
abc, abc, abc, abc, abc abc, abc, abc, abc, abc
``itertools.chain(iterA, iterB, ...)`` takes an arbitrary number of iterables as :func:`itertools.chain(iterA, iterB, ...) <itertools.chain>` takes an arbitrary
input, and returns all the elements of the first iterator, then all the elements number of iterables as input, and returns all the elements of the first
of the second, and so on, until all of the iterables have been exhausted. :: iterator, then all the elements of the second, and so on, until all of the
iterables have been exhausted. ::
itertools.chain(['a', 'b', 'c'], (1, 2, 3)) => itertools.chain(['a', 'b', 'c'], (1, 2, 3)) =>
a, b, c, 1, 2, 3 a, b, c, 1, 2, 3
``itertools.islice(iter, [start], stop, [step])`` returns a stream that's a :func:`itertools.islice(iter, [start], stop, [step]) <itertools.islice>` returns
slice of the iterator. With a single ``stop`` argument, it will return the a stream that's a slice of the iterator. With a single *stop* argument, it
first ``stop`` elements. If you supply a starting index, you'll get will return the first *stop* elements. If you supply a starting index, you'll
``stop-start`` elements, and if you supply a value for ``step``, elements will get *stop-start* elements, and if you supply a value for *step*, elements
be skipped accordingly. Unlike Python's string and list slicing, you can't use will be skipped accordingly. Unlike Python's string and list slicing, you can't
negative values for ``start``, ``stop``, or ``step``. :: use negative values for *start*, *stop*, or *step*. ::
itertools.islice(range(10), 8) => itertools.islice(range(10), 8) =>
0, 1, 2, 3, 4, 5, 6, 7 0, 1, 2, 3, 4, 5, 6, 7
@ -796,9 +793,10 @@ negative values for ``start``, ``stop``, or ``step``. ::
itertools.islice(range(10), 2, 8, 2) => itertools.islice(range(10), 2, 8, 2) =>
2, 4, 6 2, 4, 6
``itertools.tee(iter, [n])`` replicates an iterator; it returns ``n`` :func:`itertools.tee(iter, [n]) <itertools.tee>` replicates an iterator; it
independent iterators that will all return the contents of the source iterator. returns *n* independent iterators that will all return the contents of the
If you don't supply a value for ``n``, the default is 2. Replicating iterators source iterator.
If you don't supply a value for *n*, the default is 2. Replicating iterators
requires saving some of the contents of the source iterator, so this can consume requires saving some of the contents of the source iterator, so this can consume
significant memory if the iterator is large and one of the new iterators is significant memory if the iterator is large and one of the new iterators is
consumed more than the others. :: consumed more than the others. ::
@ -816,19 +814,21 @@ consumed more than the others. ::
Calling functions on elements Calling functions on elements
----------------------------- -----------------------------
The ``operator`` module contains a set of functions corresponding to Python's The :mod:`operator` module contains a set of functions corresponding to Python's
operators. Some examples are ``operator.add(a, b)`` (adds two values), operators. Some examples are :func:`operator.add(a, b) <operator.add>` (adds
``operator.ne(a, b)`` (same as ``a!=b``), and ``operator.attrgetter('id')`` two values), :func:`operator.ne(a, b) <operator.ne>` (same as ``a != b``), and
(returns a callable that fetches the ``"id"`` attribute). :func:`operator.attrgetter('id') <operator.attrgetter>`
(returns a callable that fetches the ``.id`` attribute).
``itertools.starmap(func, iter)`` assumes that the iterable will return a stream :func:`itertools.starmap(func, iter) <itertools.starmap>` assumes that the
of tuples, and calls ``f()`` using these tuples as the arguments:: iterable will return a stream of tuples, and calls *func* using these tuples as
the arguments::
itertools.starmap(os.path.join, itertools.starmap(os.path.join,
[('/usr', 'bin', 'java'), ('/bin', 'python'), [('/bin', 'python'), ('/usr', 'bin', 'java'),
('/usr', 'bin', 'perl'),('/usr', 'bin', 'ruby')]) ('/usr', 'bin', 'perl'), ('/usr', 'bin', 'ruby')])
=> =>
/usr/bin/java, /bin/python, /usr/bin/perl, /usr/bin/ruby /bin/python, /usr/bin/java, /usr/bin/perl, /usr/bin/ruby
Selecting elements Selecting elements
@ -837,20 +837,18 @@ Selecting elements
Another group of functions chooses a subset of an iterator's elements based on a Another group of functions chooses a subset of an iterator's elements based on a
predicate. predicate.
``itertools.filterfalse(predicate, iter)`` is the opposite, returning all :func:`itertools.filterfalse(predicate, iter) <itertools.filterfalse>` is the
elements for which the predicate returns false:: opposite, returning all elements for which the predicate returns false::
itertools.filterfalse(is_even, itertools.count()) => itertools.filterfalse(is_even, itertools.count()) =>
1, 3, 5, 7, 9, 11, 13, 15, ... 1, 3, 5, 7, 9, 11, 13, 15, ...
``itertools.takewhile(predicate, iter)`` returns elements for as long as the :func:`itertools.takewhile(predicate, iter) <itertools.takewhile>` returns
predicate returns true. Once the predicate returns false, the iterator will elements for as long as the predicate returns true. Once the predicate returns
signal the end of its results. false, the iterator will signal the end of its results. ::
::
def less_than_10(x): def less_than_10(x):
return (x < 10) return x < 10
itertools.takewhile(less_than_10, itertools.count()) => itertools.takewhile(less_than_10, itertools.count()) =>
0, 1, 2, 3, 4, 5, 6, 7, 8, 9 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
@ -858,10 +856,9 @@ signal the end of its results.
itertools.takewhile(is_even, itertools.count()) => itertools.takewhile(is_even, itertools.count()) =>
0 0
``itertools.dropwhile(predicate, iter)`` discards elements while the predicate :func:`itertools.dropwhile(predicate, iter) <itertools.dropwhile>` discards
returns true, and then returns the rest of the iterable's results. elements while the predicate returns true, and then returns the rest of the
iterable's results. ::
::
itertools.dropwhile(less_than_10, itertools.count()) => itertools.dropwhile(less_than_10, itertools.count()) =>
10, 11, 12, 13, 14, 15, 16, 17, 18, 19, ... 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, ...
@ -873,14 +870,14 @@ returns true, and then returns the rest of the iterable's results.
Grouping elements Grouping elements
----------------- -----------------
The last function I'll discuss, ``itertools.groupby(iter, key_func=None)``, is The last function I'll discuss, :func:`itertools.groupby(iter, key_func=None)
the most complicated. ``key_func(elem)`` is a function that can compute a key <itertools.groupby>`, is the most complicated. ``key_func(elem)`` is a function
value for each element returned by the iterable. If you don't supply a key that can compute a key value for each element returned by the iterable. If you
function, the key is simply each element itself. don't supply a key function, the key is simply each element itself.
``groupby()`` collects all the consecutive elements from the underlying iterable :func:`~itertools.groupby` collects all the consecutive elements from the
that have the same key value, and returns a stream of 2-tuples containing a key underlying iterable that have the same key value, and returns a stream of
value and an iterator for the elements with that key. 2-tuples containing a key value and an iterator for the elements with that key.
:: ::
@ -890,7 +887,7 @@ value and an iterator for the elements with that key.
... ...
] ]
def get_state (city_state): def get_state(city_state):
return city_state[1] return city_state[1]
itertools.groupby(city_list, get_state) => itertools.groupby(city_list, get_state) =>
@ -906,9 +903,9 @@ value and an iterator for the elements with that key.
iterator-3 => iterator-3 =>
('Flagstaff', 'AZ'), ('Phoenix', 'AZ'), ('Tucson', 'AZ') ('Flagstaff', 'AZ'), ('Phoenix', 'AZ'), ('Tucson', 'AZ')
``groupby()`` assumes that the underlying iterable's contents will already be :func:`~itertools.groupby` assumes that the underlying iterable's contents will
sorted based on the key. Note that the returned iterators also use the already be sorted based on the key. Note that the returned iterators also use
underlying iterable, so you have to consume the results of iterator-1 before the underlying iterable, so you have to consume the results of iterator-1 before
requesting iterator-2 and its corresponding key. requesting iterator-2 and its corresponding key.
@ -926,33 +923,34 @@ Consider a Python function ``f(a, b, c)``; you may wish to create a new function
``g(b, c)`` that's equivalent to ``f(1, b, c)``; you're filling in a value for ``g(b, c)`` that's equivalent to ``f(1, b, c)``; you're filling in a value for
one of ``f()``'s parameters. This is called "partial function application". one of ``f()``'s parameters. This is called "partial function application".
The constructor for ``partial`` takes the arguments ``(function, arg1, arg2, The constructor for :func:`~functools.partial` takes the arguments
... kwarg1=value1, kwarg2=value2)``. The resulting object is callable, so you ``(function, arg1, arg2, ..., kwarg1=value1, kwarg2=value2)``. The resulting
can just call it to invoke ``function`` with the filled-in arguments. object is callable, so you can just call it to invoke ``function`` with the
filled-in arguments.
Here's a small but realistic example:: Here's a small but realistic example::
import functools import functools
def log (message, subsystem): def log(message, subsystem):
"Write the contents of 'message' to the specified subsystem." """Write the contents of 'message' to the specified subsystem."""
print('%s: %s' % (subsystem, message)) print('%s: %s' % (subsystem, message))
... ...
server_log = functools.partial(log, subsystem='server') server_log = functools.partial(log, subsystem='server')
server_log('Unable to open socket') server_log('Unable to open socket')
``functools.reduce(func, iter, [initial_value])`` cumulatively performs an :func:`functools.reduce(func, iter, [initial_value]) <functools.reduce>`
operation on all the iterable's elements and, therefore, can't be applied to cumulatively performs an operation on all the iterable's elements and,
infinite iterables. (Note it is not in :mod:`builtins`, but in the therefore, can't be applied to infinite iterables. *func* must be a function
:mod:`functools` module.) ``func`` must be a function that takes two elements that takes two elements and returns a single value. :func:`functools.reduce`
and returns a single value. :func:`functools.reduce` takes the first two takes the first two elements A and B returned by the iterator and calculates
elements A and B returned by the iterator and calculates ``func(A, B)``. It ``func(A, B)``. It then requests the third element, C, calculates
then requests the third element, C, calculates ``func(func(A, B), C)``, combines ``func(func(A, B), C)``, combines this result with the fourth element returned,
this result with the fourth element returned, and continues until the iterable and continues until the iterable is exhausted. If the iterable returns no
is exhausted. If the iterable returns no values at all, a :exc:`TypeError` values at all, a :exc:`TypeError` exception is raised. If the initial value is
exception is raised. If the initial value is supplied, it's used as a starting supplied, it's used as a starting point and ``func(initial_value, A)`` is the
point and ``func(initial_value, A)`` is the first calculation. :: first calculation. ::
>>> import operator, functools >>> import operator, functools
>>> functools.reduce(operator.concat, ['A', 'BB', 'C']) >>> functools.reduce(operator.concat, ['A', 'BB', 'C'])
@ -978,8 +976,8 @@ built-in called :func:`sum` to compute it:
>>> sum([]) >>> sum([])
0 0
For many uses of :func:`functools.reduce`, though, it can be clearer to just write the For many uses of :func:`functools.reduce`, though, it can be clearer to just
obvious :keyword:`for` loop:: write the obvious :keyword:`for` loop::
import functools import functools
# Instead of: # Instead of:
@ -1023,28 +1021,23 @@ need to define a new function at all::
existing_files = filter(os.path.exists, file_list) existing_files = filter(os.path.exists, file_list)
If the function you need doesn't exist, you need to write it. One way to write If the function you need doesn't exist, you need to write it. One way to write
small functions is to use the ``lambda`` statement. ``lambda`` takes a number small functions is to use the :keyword:`lambda` statement. ``lambda`` takes a
of parameters and an expression combining these parameters, and creates a small number of parameters and an expression combining these parameters, and creates
function that returns the value of the expression:: an anonymous function that returns the value of the expression::
lowercase = lambda x: x.lower()
print_assign = lambda name, value: name + '=' + str(value)
adder = lambda x, y: x+y adder = lambda x, y: x+y
print_assign = lambda name, value: name + '=' + str(value)
An alternative is to just use the ``def`` statement and define a function in the An alternative is to just use the ``def`` statement and define a function in the
usual way:: usual way::
def lowercase(x): def adder(x, y):
return x.lower() return x + y
def print_assign(name, value): def print_assign(name, value):
return name + '=' + str(value) return name + '=' + str(value)
def adder(x,y):
return x + y
Which alternative is preferable? That's a style question; my usual course is to Which alternative is preferable? That's a style question; my usual course is to
avoid using ``lambda``. avoid using ``lambda``.
@ -1053,9 +1046,7 @@ functions it can define. The result has to be computable as a single
expression, which means you can't have multiway ``if... elif... else`` expression, which means you can't have multiway ``if... elif... else``
comparisons or ``try... except`` statements. If you try to do too much in a comparisons or ``try... except`` statements. If you try to do too much in a
``lambda`` statement, you'll end up with an overly complicated expression that's ``lambda`` statement, you'll end up with an overly complicated expression that's
hard to read. Quick, what's the following code doing? hard to read. Quick, what's the following code doing? ::
::
import functools import functools
total = functools.reduce(lambda a, b: (0, a[1] + b[1]), items)[1] total = functools.reduce(lambda a, b: (0, a[1] + b[1]), items)[1]
@ -1065,7 +1056,7 @@ out what's going on. Using a short nested ``def`` statements makes things a
little bit better:: little bit better::
import functools import functools
def combine (a, b): def combine(a, b):
return 0, a[1] + b[1] return 0, a[1] + b[1]
total = functools.reduce(combine, items)[1] total = functools.reduce(combine, items)[1]
@ -1085,12 +1076,12 @@ Many uses of :func:`functools.reduce` are clearer when written as ``for`` loops.
Fredrik Lundh once suggested the following set of rules for refactoring uses of Fredrik Lundh once suggested the following set of rules for refactoring uses of
``lambda``: ``lambda``:
1) Write a lambda function. 1. Write a lambda function.
2) Write a comment explaining what the heck that lambda does. 2. Write a comment explaining what the heck that lambda does.
3) Study the comment for a while, and think of a name that captures the essence 3. Study the comment for a while, and think of a name that captures the essence
of the comment. of the comment.
4) Convert the lambda to a def statement, using that name. 4. Convert the lambda to a def statement, using that name.
5) Remove the comment. 5. Remove the comment.
I really like these rules, but you're free to disagree I really like these rules, but you're free to disagree
about whether this lambda-free style is better. about whether this lambda-free style is better.

View File

@ -23,7 +23,7 @@ Using 2to3
also located in the :file:`Tools/scripts` directory of the Python root. also located in the :file:`Tools/scripts` directory of the Python root.
2to3's basic arguments are a list of files or directories to transform. The 2to3's basic arguments are a list of files or directories to transform. The
directories are to recursively traversed for Python sources. directories are recursively traversed for Python sources.
Here is a sample Python 2.x source file, :file:`example.py`:: Here is a sample Python 2.x source file, :file:`example.py`::

View File

@ -42,12 +42,13 @@ Executor Objects
Equivalent to ``map(func, *iterables)`` except *func* is executed Equivalent to ``map(func, *iterables)`` except *func* is executed
asynchronously and several calls to *func* may be made concurrently. The asynchronously and several calls to *func* may be made concurrently. The
returned iterator raises a :exc:`TimeoutError` if :meth:`__next__()` is returned iterator raises a :exc:`TimeoutError` if
called and the result isn't available after *timeout* seconds from the :meth:`~iterator.__next__` is called and the result isn't available
original call to :meth:`Executor.map`. *timeout* can be an int or a after *timeout* seconds from the original call to :meth:`Executor.map`.
float. If *timeout* is not specified or ``None``, there is no limit to *timeout* can be an int or a float. If *timeout* is not specified or
the wait time. If a call raises an exception, then that exception will ``None``, there is no limit to the wait time. If a call raises an
be raised when its value is retrieved from the iterator. exception, then that exception will be raised when its value is
retrieved from the iterator.
.. method:: shutdown(wait=True) .. method:: shutdown(wait=True)
@ -364,10 +365,11 @@ Module Functions
different :class:`Executor` instances) given by *fs* that yields futures as different :class:`Executor` instances) given by *fs* that yields futures as
they complete (finished or were cancelled). Any futures that completed they complete (finished or were cancelled). Any futures that completed
before :func:`as_completed` is called will be yielded first. The returned before :func:`as_completed` is called will be yielded first. The returned
iterator raises a :exc:`TimeoutError` if :meth:`__next__` is called and the iterator raises a :exc:`TimeoutError` if :meth:`~iterator.__next__` is
result isn't available after *timeout* seconds from the original call to called and the result isn't available after *timeout* seconds from the
:func:`as_completed`. *timeout* can be an int or float. If *timeout* is not original call to :func:`as_completed`. *timeout* can be an int or float.
specified or ``None``, there is no limit to the wait time. If *timeout* is not specified or ``None``, there is no limit to the wait
time.
.. seealso:: .. seealso::

View File

@ -660,10 +660,10 @@ the more significant byte last.
.. opcode:: FOR_ITER (delta) .. opcode:: FOR_ITER (delta)
``TOS`` is an :term:`iterator`. Call its :meth:`__next__` method. If this ``TOS`` is an :term:`iterator`. Call its :meth:`~iterator.__next__` method.
yields a new value, push it on the stack (leaving the iterator below it). If If this yields a new value, push it on the stack (leaving the iterator below
the iterator indicates it is exhausted ``TOS`` is popped, and the byte code it). If the iterator indicates it is exhausted ``TOS`` is popped, and the
counter is incremented by *delta*. byte code counter is incremented by *delta*.
.. opcode:: LOAD_GLOBAL (namei) .. opcode:: LOAD_GLOBAL (namei)

View File

@ -348,10 +348,10 @@ are always available. They are listed here in alphabetical order.
.. function:: enumerate(iterable, start=0) .. function:: enumerate(iterable, start=0)
Return an enumerate object. *iterable* must be a sequence, an Return an enumerate object. *iterable* must be a sequence, an
:term:`iterator`, or some other object which supports iteration. The :term:`iterator`, or some other object which supports iteration.
:meth:`__next__` method of the iterator returned by :func:`enumerate` returns a The :meth:`~iterator.__next__` method of the iterator returned by
tuple containing a count (from *start* which defaults to 0) and the :func:`enumerate` returns a tuple containing a count (from *start* which
values obtained from iterating over *iterable*. defaults to 0) and the values obtained from iterating over *iterable*.
>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter'] >>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
>>> list(enumerate(seasons)) >>> list(enumerate(seasons))
@ -683,9 +683,10 @@ are always available. They are listed here in alphabetical order.
starting at ``0``). If it does not support either of those protocols, starting at ``0``). If it does not support either of those protocols,
:exc:`TypeError` is raised. If the second argument, *sentinel*, is given, :exc:`TypeError` is raised. If the second argument, *sentinel*, is given,
then *object* must be a callable object. The iterator created in this case then *object* must be a callable object. The iterator created in this case
will call *object* with no arguments for each call to its :meth:`__next__` will call *object* with no arguments for each call to its
method; if the value returned is equal to *sentinel*, :exc:`StopIteration` :meth:`~iterator.__next__` method; if the value returned is equal to
will be raised, otherwise the value will be returned. *sentinel*, :exc:`StopIteration` will be raised, otherwise the value will
be returned.
One useful application of the second form of :func:`iter` is to read lines of One useful application of the second form of :func:`iter` is to read lines of
a file until a certain line is reached. The following example reads a file a file until a certain line is reached. The following example reads a file
@ -779,9 +780,9 @@ are always available. They are listed here in alphabetical order.
.. function:: next(iterator[, default]) .. function:: next(iterator[, default])
Retrieve the next item from the *iterator* by calling its :meth:`__next__` Retrieve the next item from the *iterator* by calling its
method. If *default* is given, it is returned if the iterator is exhausted, :meth:`~iterator.__next__` method. If *default* is given, it is returned
otherwise :exc:`StopIteration` is raised. if the iterator is exhausted, otherwise :exc:`StopIteration` is raised.
.. function:: object() .. function:: object()

View File

@ -779,9 +779,9 @@ specific sequence types, dictionaries, and other more specialized forms. The
specific types are not important beyond their implementation of the iterator specific types are not important beyond their implementation of the iterator
protocol. protocol.
Once an iterator's :meth:`__next__` method raises :exc:`StopIteration`, it must Once an iterator's :meth:`~iterator.__next__` method raises
continue to do so on subsequent calls. Implementations that do not obey this :exc:`StopIteration`, it must continue to do so on subsequent calls.
property are deemed broken. Implementations that do not obey this property are deemed broken.
.. _generator-types: .. _generator-types:
@ -792,7 +792,8 @@ Generator Types
Python's :term:`generator`\s provide a convenient way to implement the iterator Python's :term:`generator`\s provide a convenient way to implement the iterator
protocol. If a container object's :meth:`__iter__` method is implemented as a protocol. If a container object's :meth:`__iter__` method is implemented as a
generator, it will automatically return an iterator object (technically, a generator, it will automatically return an iterator object (technically, a
generator object) supplying the :meth:`__iter__` and :meth:`__next__` methods. generator object) supplying the :meth:`__iter__` and :meth:`~generator.__next__`
methods.
More information about generators can be found in :ref:`the documentation for More information about generators can be found in :ref:`the documentation for
the yield expression <yieldexpr>`. the yield expression <yieldexpr>`.

View File

@ -600,9 +600,9 @@ Callable types
A function or method which uses the :keyword:`yield` statement (see section A function or method which uses the :keyword:`yield` statement (see section
:ref:`yield`) is called a :dfn:`generator function`. Such a function, when :ref:`yield`) is called a :dfn:`generator function`. Such a function, when
called, always returns an iterator object which can be used to execute the called, always returns an iterator object which can be used to execute the
body of the function: calling the iterator's :meth:`__next__` method will body of the function: calling the iterator's :meth:`iterator__next__`
cause the function to execute until it provides a value using the method will cause the function to execute until it provides a value
:keyword:`yield` statement. When the function executes a using the :keyword:`yield` statement. When the function executes a
:keyword:`return` statement or falls off the end, a :exc:`StopIteration` :keyword:`return` statement or falls off the end, a :exc:`StopIteration`
exception is raised and the iterator will have reached the end of the set of exception is raised and the iterator will have reached the end of the set of
values to be returned. values to be returned.
@ -1189,7 +1189,7 @@ Basic customization
builtin: print builtin: print
Called by the :func:`format` built-in function (and by extension, the Called by the :func:`format` built-in function (and by extension, the
:meth:`format` method of class :class:`str`) to produce a "formatted" :meth:`str.format` method of class :class:`str`) to produce a "formatted"
string representation of an object. The ``format_spec`` argument is string representation of an object. The ``format_spec`` argument is
a string that contains a description of the formatting options desired. a string that contains a description of the formatting options desired.
The interpretation of the ``format_spec`` argument is up to the type The interpretation of the ``format_spec`` argument is up to the type

View File

@ -294,13 +294,13 @@ for comprehensions, except that it is enclosed in parentheses instead of
brackets or curly braces. brackets or curly braces.
Variables used in the generator expression are evaluated lazily when the Variables used in the generator expression are evaluated lazily when the
:meth:`__next__` method is called for generator object (in the same fashion as :meth:`~generator.__next__` method is called for generator object (in the same
normal generators). However, the leftmost :keyword:`for` clause is immediately fashion as normal generators). However, the leftmost :keyword:`for` clause is
evaluated, so that an error produced by it can be seen before any other possible immediately evaluated, so that an error produced by it can be seen before any
error in the code that handles the generator expression. Subsequent other possible error in the code that handles the generator expression.
:keyword:`for` clauses cannot be evaluated immediately since they may depend on Subsequent :keyword:`for` clauses cannot be evaluated immediately since they
the previous :keyword:`for` loop. For example: ``(x*y for x in range(10) for y may depend on the previous :keyword:`for` loop. For example: ``(x*y for x in
in bar(x))``. range(10) for y in bar(x))``.
The parentheses can be omitted on calls with only one argument. See section The parentheses can be omitted on calls with only one argument. See section
:ref:`calls` for the detail. :ref:`calls` for the detail.
@ -394,10 +394,11 @@ is already executing raises a :exc:`ValueError` exception.
Starts the execution of a generator function or resumes it at the last Starts the execution of a generator function or resumes it at the last
executed :keyword:`yield` expression. When a generator function is resumed executed :keyword:`yield` expression. When a generator function is resumed
with a :meth:`__next__` method, the current :keyword:`yield` expression with a :meth:`~generator.__next__` method, the current :keyword:`yield`
always evaluates to :const:`None`. The execution then continues to the next expression always evaluates to :const:`None`. The execution then continues
:keyword:`yield` expression, where the generator is suspended again, and the to the next :keyword:`yield` expression, where the generator is suspended
value of the :token:`expression_list` is returned to :meth:`next`'s caller. again, and the value of the :token:`expression_list` is returned to
:meth:`next`'s caller.
If the generator exits without yielding another value, a :exc:`StopIteration` If the generator exits without yielding another value, a :exc:`StopIteration`
exception is raised. exception is raised.

View File

@ -737,11 +737,11 @@ using a :keyword:`for` statement::
This style of access is clear, concise, and convenient. The use of iterators This style of access is clear, concise, and convenient. The use of iterators
pervades and unifies Python. Behind the scenes, the :keyword:`for` statement pervades and unifies Python. Behind the scenes, the :keyword:`for` statement
calls :func:`iter` on the container object. The function returns an iterator calls :func:`iter` on the container object. The function returns an iterator
object that defines the method :meth:`__next__` which accesses elements in the object that defines the method :meth:`~iterator.__next__` which accesses
container one at a time. When there are no more elements, :meth:`__next__` elements in the container one at a time. When there are no more elements,
raises a :exc:`StopIteration` exception which tells the :keyword:`for` loop to :meth:`__next__` raises a :exc:`StopIteration` exception which tells the
terminate. You can call the :meth:`__next__` method using the :func:`next` :keyword:`for` loop to terminate. You can call the :meth:`__next__` method
built-in function; this example shows how it all works:: using the :func:`next` built-in function; this example shows how it all works::
>>> s = 'abc' >>> s = 'abc'
>>> it = iter(s) >>> it = iter(s)
@ -761,8 +761,8 @@ built-in function; this example shows how it all works::
Having seen the mechanics behind the iterator protocol, it is easy to add Having seen the mechanics behind the iterator protocol, it is easy to add
iterator behavior to your classes. Define an :meth:`__iter__` method which iterator behavior to your classes. Define an :meth:`__iter__` method which
returns an object with a :meth:`__next__` method. If the class defines returns an object with a :meth:`~iterator.__next__` method. If the class
:meth:`__next__`, then :meth:`__iter__` can just return ``self``:: defines :meth:`__next__`, then :meth:`__iter__` can just return ``self``::
class Reverse: class Reverse:
"""Iterator for looping over a sequence backwards.""" """Iterator for looping over a sequence backwards."""
@ -819,8 +819,8 @@ easy to create::
Anything that can be done with generators can also be done with class based Anything that can be done with generators can also be done with class based
iterators as described in the previous section. What makes generators so iterators as described in the previous section. What makes generators so
compact is that the :meth:`__iter__` and :meth:`__next__` methods are created compact is that the :meth:`__iter__` and :meth:`~generator.__next__` methods
automatically. are created automatically.
Another key feature is that the local variables and execution state are Another key feature is that the local variables and execution state are
automatically saved between calls. This made the function easier to write and automatically saved between calls. This made the function easier to write and

View File

@ -771,7 +771,7 @@ Operators And Special Methods
respectively). respectively).
* :pep:`3114`: the standard :meth:`next` method has been renamed to * :pep:`3114`: the standard :meth:`next` method has been renamed to
:meth:`__next__`. :meth:`~iterator.__next__`.
* The :meth:`__oct__` and :meth:`__hex__` special methods are removed * The :meth:`__oct__` and :meth:`__hex__` special methods are removed
-- :func:`oct` and :func:`hex` use :meth:`__index__` now to convert -- :func:`oct` and :func:`hex` use :meth:`__index__` now to convert
@ -807,7 +807,7 @@ Builtins
To get the old behavior of :func:`input`, use ``eval(input())``. To get the old behavior of :func:`input`, use ``eval(input())``.
* A new built-in function :func:`next` was added to call the * A new built-in function :func:`next` was added to call the
:meth:`__next__` method on an object. :meth:`~iterator.__next__` method on an object.
* The :func:`round` function rounding strategy and return type have * The :func:`round` function rounding strategy and return type have
changed. Exact halfway cases are now rounded to the nearest even changed. Exact halfway cases are now rounded to the nearest even

View File

@ -595,8 +595,13 @@ def win32_ver(release='',version='',csd='',ptype=''):
release = '7' release = '7'
else: else:
release = '2008ServerR2' release = '2008ServerR2'
elif min == 2:
if product_type == VER_NT_WORKSTATION:
release = '8'
else:
release = '2012Server'
else: else:
release = 'post2008Server' release = 'post2012Server'
else: else:
if not release: if not release:

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@ -565,10 +565,10 @@ class RunPathTestCase(unittest.TestCase, CodeExecutionMixin):
with open(filename, 'w', encoding='latin1') as f: with open(filename, 'w', encoding='latin1') as f:
f.write(""" f.write("""
#coding:latin1 #coding:latin1
"non-ASCII: h\xe9" s = "non-ASCII: h\xe9"
""") """)
result = run_path(filename) result = run_path(filename)
self.assertEqual(result['__doc__'], "non-ASCII: h\xe9") self.assertEqual(result['s'], "non-ASCII: h\xe9")
def test_main(): def test_main():

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@ -250,6 +250,7 @@ class TestTimeit(unittest.TestCase):
s = self.run_main(seconds_per_increment=60.0, switches=['-r-5']) s = self.run_main(seconds_per_increment=60.0, switches=['-r-5'])
self.assertEqual(s, "10 loops, best of 1: 60 sec per loop\n") self.assertEqual(s, "10 loops, best of 1: 60 sec per loop\n")
@unittest.skipIf(sys.flags.optimize >= 2, "need __doc__")
def test_main_help(self): def test_main_help(self):
s = self.run_main(switches=['-h']) s = self.run_main(switches=['-h'])
# Note: It's not clear that the trailing space was intended as part of # Note: It's not clear that the trailing space was intended as part of