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Add section on operator module; make a few edits

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Andrew M. Kuchling 2006-11-08 14:14:30 +00:00
parent f4dcd1dc30
commit 9efdd7880d
1 changed files with 38 additions and 8 deletions
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Doc/howto/functional.rst
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@ -339,11 +339,11 @@ the set's elements::
Generator expressions and list comprehensions
----------------------------------------------------
Two common operations on a stream are 1) performing some operation for
every element, 2) selecting a subset of elements that meet some
condition. For example, given a list of strings, you might want to
strip off trailing whitespace from each line or extract all the
strings containing a given substring.
Two common operations on an iterator's output are 1) performing some
operation for every element, 2) selecting a subset of elements that
meet some condition. For example, given a list of strings, you might
want to strip off trailing whitespace from each line or extract all
the strings containing a given substring.
List comprehensions and generator expressions (short form: "listcomps"
and "genexps") are a concise notation for such operations, borrowed
@ -941,6 +941,12 @@ and returns them in a tuple::
itertools.izip(['a', 'b', 'c'], (1, 2, 3)) =>
('a', 1), ('b', 2), ('c', 3)
It's similiar to the built-in ``zip()`` function, but doesn't
construct an in-memory list and exhaust all the input iterators before
returning; instead tuples are constructed and returned only if they're
requested. (The technical term for this behaviour is
`lazy evaluation <http://en.wikipedia.org/wiki/Lazy_evaluation>`__.)
This iterator is intended to be used with iterables that are all of
the same length. If the iterables are of different lengths, the
resulting stream will be the same length as the shortest iterable.
@ -1138,7 +1144,30 @@ Here's a small but realistic example::
There are also third-party modules, such as Collin Winter's
`functional package <http://cheeseshop.python.org/pypi/functional>`__,
that are intended for use in functional-style programs.
that are intended for use in functional-style programs. See below
for a section describing the ``functional`` mdoule.
The operator module
===================
The ``operator`` module was mentioned earlier. It contains a set of
functions corresponding to Python's operators. These functions
are often useful in functional-style code because they save you
from writing trivial functions that perform a single operation.
Some of the functions in this module are:
* Math operations: ``add()``, ``sub()``, ``mul()``, ``div()``, ``floordiv()``,
``abs()``, ...
* Logical operations: ``not_()``, ``truth()``.
* Bitwise operations: ``and_()``, ``or_()``, ``invert()``.
* Comparisons: ``eq()``, ``ne()``, ``lt()``, ``le()``, ``gt()``, and ``ge()``.
* Object identity: ``is_()``, ``is_not()``.
Consult `the operator module's documentation <http://docs.python.org/lib/module-operator.html>`__ for a complete
list.
The functional module
@ -1297,8 +1326,9 @@ sections into one. Typo fixes.
Version 0.21: Added more references suggested on the tutor mailing list.
Version 0.30: Adds a section on the ``functional`` module written by
Collin Winter.
Version 0.30: Adds a section on the ``functional`` module written by
Collin Winter; adds short section on the operator module; a few other
edits.
References