mirror of https://github.com/python/cpython
Add examples.
This commit is contained in:
Raymond Hettinger
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040f10e9b3
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@ -71,6 +71,7 @@ loops that truncate the stream.
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Equivalent to::
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def chain(*iterables):
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# chain('ABC', 'DEF') --> A B C D E F
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for it in iterables:
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for element in it:
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yield element
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@ -83,6 +84,7 @@ loops that truncate the stream.
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@classmethod
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def from_iterable(iterables):
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# chain.from_iterable(['ABC', 'DEF']) --> A B C D E F
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for it in iterables:
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for element in it:
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yield element
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@ -108,7 +110,8 @@ loops that truncate the stream.
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Equivalent to::
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def combinations(iterable, r):
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'combinations(range(4), 3) --> (0,1,2) (0,1,3) (0,2,3) (1,2,3)'
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# combinations('ABCD', 2) --> AB AC AD BC BD CD
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# combinations(range(4), 3) --> 012 013 023 123
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pool = tuple(iterable)
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n = len(pool)
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indices = range(r)
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@ -145,6 +148,7 @@ loops that truncate the stream.
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numbers. Equivalent to::
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def count(n=0):
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# count(10) --> 10 11 12 13 14 ...
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while True:
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yield n
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n += 1
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@ -157,6 +161,7 @@ loops that truncate the stream.
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indefinitely. Equivalent to::
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def cycle(iterable):
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# cycle('ABCD') --> A B C D A B C D A B C D ...
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saved = []
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for element in iterable:
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yield element
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@ -177,6 +182,7 @@ loops that truncate the stream.
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start-up time. Equivalent to::
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def dropwhile(predicate, iterable):
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# dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1
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iterable = iter(iterable)
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for x in iterable:
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if not predicate(x):
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@ -215,6 +221,8 @@ loops that truncate the stream.
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:func:`groupby` is equivalent to::
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class groupby(object):
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# [k for k, g in groupby('AAAABBBCCDAABBB')] --> A B C D A B
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# [(list(g)) for k, g in groupby('AAAABBBCCD')] --> AAAA BBB CC D
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def __init__(self, iterable, key=None):
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if key is None:
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key = lambda x: x
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@ -245,6 +253,7 @@ loops that truncate the stream.
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that are true. Equivalent to::
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def ifilter(predicate, iterable):
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# ifilter(lambda x: x%2, range(10)) --> 1 3 5 7 9
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if predicate is None:
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predicate = bool
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for x in iterable:
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@ -259,6 +268,7 @@ loops that truncate the stream.
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that are false. Equivalent to::
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def ifilterfalse(predicate, iterable):
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# ifilterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8
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if predicate is None:
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predicate = bool
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for x in iterable:
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@ -277,6 +287,7 @@ loops that truncate the stream.
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useful way of supplying arguments to :func:`imap`. Equivalent to::
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def imap(function, *iterables):
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# imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000
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iterables = map(iter, iterables)
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while True:
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args = [it.next() for it in iterables]
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@ -299,6 +310,10 @@ loops that truncate the stream.
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multi-line report may list a name field on every third line). Equivalent to::
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def islice(iterable, *args):
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# islice('ABCDEFG', 2) --> A B
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# islice('ABCDEFG', 2, 4) --> C D
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# islice('ABCDEFG', 2, None) --> C D E F G
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# islice('ABCDEFG', 0, None, 2) --> A C E G
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s = slice(*args)
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it = iter(xrange(s.start or 0, s.stop or sys.maxint, s.step or 1))
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nexti = it.next()
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@ -321,6 +336,7 @@ loops that truncate the stream.
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lock-step iteration over several iterables at a time. Equivalent to::
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def izip(*iterables):
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# izip('ABCD', 'xy') --> Ax By
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iterables = map(iter, iterables)
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while iterables:
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result = [it.next() for it in iterables]
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@ -346,6 +362,7 @@ loops that truncate the stream.
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Iteration continues until the longest iterable is exhausted. Equivalent to::
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def izip_longest(*args, **kwds):
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# izip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-
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fillvalue = kwds.get('fillvalue')
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def sentinel(counter = ([fillvalue]*(len(args)-1)).pop):
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yield counter() # yields the fillvalue, or raises IndexError
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@ -382,7 +399,8 @@ loops that truncate the stream.
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Equivalent to::
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def permutations(iterable, r=None):
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'permutations(range(3), 2) --> (0,1) (0,2) (1,0) (1,2) (2,0) (2,1)'
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# permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
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# permutations(range(3)) --> 012 021 102 120 201 210
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pool = tuple(iterable)
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n = len(pool)
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r = n if r is None else r
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@ -424,8 +442,8 @@ loops that truncate the stream.
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Equivalent to nested for-loops in a generator expression. For example,
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``product(A, B)`` returns the same as ``((x,y) for x in A for y in B)``.
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The leftmost iterators are in the outermost for-loop, so the output tuples
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cycle like an odometer (with the rightmost element changing on every
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The leftmost iterators correspond to the outermost for-loop, so the output
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tuples cycle like an odometer (with the rightmost element changing on every
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iteration). This results in a lexicographic ordering so that if the
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inputs iterables are sorted, the product tuples are emitted
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in sorted order.
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@ -438,6 +456,8 @@ loops that truncate the stream.
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actual implementation does not build up intermediate results in memory::
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def product(*args, **kwds):
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# product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
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# product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
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pools = map(tuple, args) * kwds.get('repeat', 1)
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result = [[]]
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for pool in pools:
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@ -451,10 +471,11 @@ loops that truncate the stream.
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Make an iterator that returns *object* over and over again. Runs indefinitely
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unless the *times* argument is specified. Used as argument to :func:`imap` for
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invariant parameters to the called function. Also used with :func:`izip` to
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create an invariant part of a tuple record. Equivalent to::
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invariant function parameters. Also used with :func:`izip` to create constant
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fields in a tuple record. Equivalent to::
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def repeat(object, times=None):
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# repeat(10, 3) --> 10 10 10
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if times is None:
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while True:
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yield object
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@ -472,6 +493,7 @@ loops that truncate the stream.
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between ``function(a,b)`` and ``function(*c)``. Equivalent to::
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def starmap(function, iterable):
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# starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000
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for args in iterable:
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yield function(*args)
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@ -485,6 +507,7 @@ loops that truncate the stream.
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predicate is true. Equivalent to::
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def takewhile(predicate, iterable):
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# takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4
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for x in iterable:
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if predicate(x):
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yield x
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@ -528,23 +551,6 @@ Examples
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The following examples show common uses for each tool and demonstrate ways they
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can be combined. ::
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>>> amounts = [120.15, 764.05, 823.14]
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>>> for checknum, amount in izip(count(1200), amounts):
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... print 'Check %d is for $%.2f' % (checknum, amount)
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...
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Check 1200 is for $120.15
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Check 1201 is for $764.05
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Check 1202 is for $823.14
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>>> import operator
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>>> for cube in imap(operator.pow, xrange(1,5), repeat(3)):
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... print cube
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...
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1
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8
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27
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64
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# Show a dictionary sorted and grouped by value
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>>> from operator import itemgetter
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>>> d = dict(a=1, b=2, c=1, d=2, e=1, f=2, g=3)
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