# Copyright (C) 2001-2018, Python Software Foundation # For licence information, see README file. # #, fuzzy msgid "" msgstr "" "Project-Id-Version: Python 3.6\n" "Report-Msgid-Bugs-To: \n" "POT-Creation-Date: 2017-10-13 22:28+0200\n" "PO-Revision-Date: 2018-02-15 00:38+0100\n" "Last-Translator: FULL NAME \n" "Language-Team: FRENCH \n" "Language: fr\n" "MIME-Version: 1.0\n" "Content-Type: text/plain; charset=UTF-8\n" "Content-Transfer-Encoding: 8bit\n" #: ../Doc/howto/functional.rst:3 msgid "Functional Programming HOWTO" msgstr "" #: ../Doc/howto/functional.rst:0 msgid "Author" msgstr "Auteur" #: ../Doc/howto/functional.rst:5 msgid "A. M. Kuchling" msgstr "" #: ../Doc/howto/functional.rst:0 msgid "Release" msgstr "Version" #: ../Doc/howto/functional.rst:6 msgid "0.32" msgstr "" #: ../Doc/howto/functional.rst:8 msgid "" "In this document, we'll take a tour of Python's features suitable for " "implementing programs in a functional style. After an introduction to the " "concepts of functional programming, we'll look at language features such as :" "term:`iterator`\\s and :term:`generator`\\s and relevant library modules " "such as :mod:`itertools` and :mod:`functools`." msgstr "" #: ../Doc/howto/functional.rst:16 msgid "Introduction" msgstr "Introduction" #: ../Doc/howto/functional.rst:18 msgid "" "This section explains the basic concept of functional programming; if you're " "just interested in learning about Python language features, skip to the next " "section on :ref:`functional-howto-iterators`." msgstr "" #: ../Doc/howto/functional.rst:22 msgid "" "Programming languages support decomposing problems in several different ways:" msgstr "" #: ../Doc/howto/functional.rst:24 msgid "" "Most programming languages are **procedural**: programs are lists of " "instructions that tell the computer what to do with the program's input. C, " "Pascal, and even Unix shells are procedural languages." msgstr "" #: ../Doc/howto/functional.rst:28 msgid "" "In **declarative** languages, you write a specification that describes the " "problem to be solved, and the language implementation figures out how to " "perform the computation efficiently. SQL is the declarative language you're " "most likely to be familiar with; a SQL query describes the data set you want " "to retrieve, and the SQL engine decides whether to scan tables or use " "indexes, which subclauses should be performed first, etc." msgstr "" #: ../Doc/howto/functional.rst:35 msgid "" "**Object-oriented** programs manipulate collections of objects. Objects " "have internal state and support methods that query or modify this internal " "state in some way. Smalltalk and Java are object-oriented languages. C++ " "and Python are languages that support object-oriented programming, but don't " "force the use of object-oriented features." msgstr "" #: ../Doc/howto/functional.rst:41 msgid "" "**Functional** programming decomposes a problem into a set of functions. " "Ideally, functions only take inputs and produce outputs, and don't have any " "internal state that affects the output produced for a given input. Well-" "known functional languages include the ML family (Standard ML, OCaml, and " "other variants) and Haskell." msgstr "" #: ../Doc/howto/functional.rst:47 msgid "" "The designers of some computer languages choose to emphasize one particular " "approach to programming. This often makes it difficult to write programs " "that use a different approach. Other languages are multi-paradigm languages " "that support several different approaches. Lisp, C++, and Python are multi-" "paradigm; you can write programs or libraries that are largely procedural, " "object-oriented, or functional in all of these languages. In a large " "program, different sections might be written using different approaches; the " "GUI might be object-oriented while the processing logic is procedural or " "functional, for example." msgstr "" #: ../Doc/howto/functional.rst:58 msgid "" "In a functional program, input flows through a set of functions. Each " "function operates on its input and produces some output. Functional style " "discourages functions with side effects that modify internal state or make " "other changes that aren't visible in the function's return value. Functions " "that have no side effects at all are called **purely functional**. Avoiding " "side effects means not using data structures that get updated as a program " "runs; every function's output must only depend on its input." msgstr "" #: ../Doc/howto/functional.rst:66 msgid "" "Some languages are very strict about purity and don't even have assignment " "statements such as ``a=3`` or ``c = a + b``, but it's difficult to avoid all " "side effects. Printing to the screen or writing to a disk file are side " "effects, for example. For example, in Python a call to the :func:`print` " "or :func:`time.sleep` function both return no useful value; they're only " "called for their side effects of sending some text to the screen or pausing " "execution for a second." msgstr "" #: ../Doc/howto/functional.rst:74 msgid "" "Python programs written in functional style usually won't go to the extreme " "of avoiding all I/O or all assignments; instead, they'll provide a " "functional-appearing interface but will use non-functional features " "internally. For example, the implementation of a function will still use " "assignments to local variables, but won't modify global variables or have " "other side effects." msgstr "" #: ../Doc/howto/functional.rst:80 msgid "" "Functional programming can be considered the opposite of object-oriented " "programming. Objects are little capsules containing some internal state " "along with a collection of method calls that let you modify this state, and " "programs consist of making the right set of state changes. Functional " "programming wants to avoid state changes as much as possible and works with " "data flowing between functions. In Python you might combine the two " "approaches by writing functions that take and return instances representing " "objects in your application (e-mail messages, transactions, etc.)." msgstr "" #: ../Doc/howto/functional.rst:89 msgid "" "Functional design may seem like an odd constraint to work under. Why should " "you avoid objects and side effects? There are theoretical and practical " "advantages to the functional style:" msgstr "" #: ../Doc/howto/functional.rst:93 msgid "Formal provability." msgstr "" #: ../Doc/howto/functional.rst:94 msgid "Modularity." msgstr "" #: ../Doc/howto/functional.rst:95 msgid "Composability." msgstr "" #: ../Doc/howto/functional.rst:96 msgid "Ease of debugging and testing." msgstr "" #: ../Doc/howto/functional.rst:100 msgid "Formal provability" msgstr "" #: ../Doc/howto/functional.rst:102 msgid "" "A theoretical benefit is that it's easier to construct a mathematical proof " "that a functional program is correct." msgstr "" #: ../Doc/howto/functional.rst:105 msgid "" "For a long time researchers have been interested in finding ways to " "mathematically prove programs correct. This is different from testing a " "program on numerous inputs and concluding that its output is usually " "correct, or reading a program's source code and concluding that the code " "looks right; the goal is instead a rigorous proof that a program produces " "the right result for all possible inputs." msgstr "" #: ../Doc/howto/functional.rst:112 msgid "" "The technique used to prove programs correct is to write down " "**invariants**, properties of the input data and of the program's variables " "that are always true. For each line of code, you then show that if " "invariants X and Y are true **before** the line is executed, the slightly " "different invariants X' and Y' are true **after** the line is executed. " "This continues until you reach the end of the program, at which point the " "invariants should match the desired conditions on the program's output." msgstr "" #: ../Doc/howto/functional.rst:120 msgid "" "Functional programming's avoidance of assignments arose because assignments " "are difficult to handle with this technique; assignments can break " "invariants that were true before the assignment without producing any new " "invariants that can be propagated onward." msgstr "" #: ../Doc/howto/functional.rst:125 msgid "" "Unfortunately, proving programs correct is largely impractical and not " "relevant to Python software. Even trivial programs require proofs that are " "several pages long; the proof of correctness for a moderately complicated " "program would be enormous, and few or none of the programs you use daily " "(the Python interpreter, your XML parser, your web browser) could be proven " "correct. Even if you wrote down or generated a proof, there would then be " "the question of verifying the proof; maybe there's an error in it, and you " "wrongly believe you've proved the program correct." msgstr "" #: ../Doc/howto/functional.rst:136 msgid "Modularity" msgstr "" #: ../Doc/howto/functional.rst:138 msgid "" "A more practical benefit of functional programming is that it forces you to " "break apart your problem into small pieces. Programs are more modular as a " "result. It's easier to specify and write a small function that does one " "thing than a large function that performs a complicated transformation. " "Small functions are also easier to read and to check for errors." msgstr "" #: ../Doc/howto/functional.rst:146 msgid "Ease of debugging and testing" msgstr "" #: ../Doc/howto/functional.rst:148 msgid "Testing and debugging a functional-style program is easier." msgstr "" #: ../Doc/howto/functional.rst:150 msgid "" "Debugging is simplified because functions are generally small and clearly " "specified. When a program doesn't work, each function is an interface point " "where you can check that the data are correct. You can look at the " "intermediate inputs and outputs to quickly isolate the function that's " "responsible for a bug." msgstr "" #: ../Doc/howto/functional.rst:155 msgid "" "Testing is easier because each function is a potential subject for a unit " "test. Functions don't depend on system state that needs to be replicated " "before running a test; instead you only have to synthesize the right input " "and then check that the output matches expectations." msgstr "" #: ../Doc/howto/functional.rst:162 msgid "Composability" msgstr "" #: ../Doc/howto/functional.rst:164 msgid "" "As you work on a functional-style program, you'll write a number of " "functions with varying inputs and outputs. Some of these functions will be " "unavoidably specialized to a particular application, but others will be " "useful in a wide variety of programs. For example, a function that takes a " "directory path and returns all the XML files in the directory, or a function " "that takes a filename and returns its contents, can be applied to many " "different situations." msgstr "" #: ../Doc/howto/functional.rst:171 msgid "" "Over time you'll form a personal library of utilities. Often you'll " "assemble new programs by arranging existing functions in a new configuration " "and writing a few functions specialized for the current task." msgstr "" #: ../Doc/howto/functional.rst:179 msgid "Iterators" msgstr "Itérateurs" #: ../Doc/howto/functional.rst:181 msgid "" "I'll start by looking at a Python language feature that's an important " "foundation for writing functional-style programs: iterators." msgstr "" #: ../Doc/howto/functional.rst:184 msgid "" "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 :meth:`~iterator.__next__` that takes no arguments and always returns " "the next element of the stream. If there are no more elements in the " "stream, :meth:`~iterator.__next__` must raise the :exc:`StopIteration` " "exception. Iterators don't have to be finite, though; it's perfectly " "reasonable to write an iterator that produces an infinite stream of data." msgstr "" #: ../Doc/howto/functional.rst:192 msgid "" "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 :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 dictionaries. An object is called :term:`iterable` if you can get " "an iterator for it." msgstr "" #: ../Doc/howto/functional.rst:199 msgid "You can experiment with the iteration interface manually:" msgstr "" #: ../Doc/howto/functional.rst:217 msgid "" "Python expects iterable objects in several different contexts, the most " "important being the :keyword:`for` statement. In the statement ``for X in " "Y``, Y must be an iterator or some object for which :func:`iter` can create " "an iterator. These two statements are equivalent::" msgstr "" #: ../Doc/howto/functional.rst:229 msgid "" "Iterators can be materialized as lists or tuples by using the :func:`list` " "or :func:`tuple` constructor functions:" msgstr "" #: ../Doc/howto/functional.rst:238 msgid "" "Sequence unpacking also supports iterators: if you know an iterator will " "return N elements, you can unpack them into an N-tuple:" msgstr "" #: ../Doc/howto/functional.rst:247 msgid "" "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\"`` 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 problems if the iterator is infinite; :func:`max`, :" "func:`min` will never return, and if the element X never appears in the " "stream, the ``\"in\"`` and ``\"not in\"`` operators won't return either." msgstr "" #: ../Doc/howto/functional.rst:255 msgid "" "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 can optionally provide these additional capabilities, but the " "iterator protocol only specifies the :meth:`~iterator.__next__` method. " "Functions may therefore consume all of the iterator's output, and if you " "need to do something different with the same stream, you'll have to create a " "new iterator." msgstr "" #: ../Doc/howto/functional.rst:265 msgid "Data Types That Support Iterators" msgstr "" #: ../Doc/howto/functional.rst:267 msgid "" "We've already seen how lists and tuples support iterators. In fact, any " "Python sequence type, such as strings, will automatically support creation " "of an iterator." msgstr "" #: ../Doc/howto/functional.rst:271 msgid "" "Calling :func:`iter` on a dictionary returns an iterator that will loop over " "the dictionary's keys::" msgstr "" #: ../Doc/howto/functional.rst:291 msgid "" "Note that the order is essentially random, because it's based on the hash " "ordering of the objects in the dictionary." msgstr "" #: ../Doc/howto/functional.rst:294 msgid "" "Applying :func:`iter` to a dictionary always loops over the keys, but " "dictionaries have methods that return other iterators. If you want to " "iterate over values or key/value pairs, you can explicitly call the :meth:" "`~dict.values` or :meth:`~dict.items` methods to get an appropriate iterator." msgstr "" #: ../Doc/howto/functional.rst:300 msgid "" "The :func:`dict` constructor can accept an iterator that returns a finite " "stream of ``(key, value)`` tuples:" msgstr "" #: ../Doc/howto/functional.rst:307 msgid "" "Files also support iteration by calling the :meth:`~io.TextIOBase.readline` " "method until there are no more lines in the file. This means you can read " "each line of a file like this::" msgstr "" #: ../Doc/howto/functional.rst:315 msgid "" "Sets can take their contents from an iterable and let you iterate over the " "set's elements::" msgstr "" #: ../Doc/howto/functional.rst:325 msgid "Generator expressions and list comprehensions" msgstr "" #: ../Doc/howto/functional.rst:327 msgid "" "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." msgstr "" #: ../Doc/howto/functional.rst:333 msgid "" "List comprehensions and generator expressions (short form: \"listcomps\" and " "\"genexps\") are a concise notation for such operations, borrowed from the " "functional programming language Haskell (https://www.haskell.org/). You can " "strip all the whitespace from a stream of strings with the following code::" msgstr "" #: ../Doc/howto/functional.rst:346 msgid "" "You can select only certain elements by adding an ``\"if\"`` condition::" msgstr "" #: ../Doc/howto/functional.rst:351 msgid "" "With a list comprehension, you get back a Python list; ``stripped_list`` is " "a list containing the resulting lines, not an iterator. Generator " "expressions return an iterator that computes the values as necessary, not " "needing to materialize all the values at once. This means that list " "comprehensions aren't useful if you're working with iterators that return an " "infinite stream or a very large amount of data. Generator expressions are " "preferable in these situations." msgstr "" #: ../Doc/howto/functional.rst:358 msgid "" "Generator expressions are surrounded by parentheses (\"()\") and list " "comprehensions are surrounded by square brackets (\"[]\"). Generator " "expressions have the form::" msgstr "" #: ../Doc/howto/functional.rst:371 msgid "" "Again, for a list comprehension only the outside brackets are different " "(square brackets instead of parentheses)." msgstr "" #: ../Doc/howto/functional.rst:374 msgid "" "The elements of the generated output will be the successive values of " "``expression``. The ``if`` clauses are all optional; if present, " "``expression`` is only evaluated and added to the result when ``condition`` " "is true." msgstr "" #: ../Doc/howto/functional.rst:378 msgid "" "Generator expressions always have to be written inside parentheses, but the " "parentheses signalling a function call also count. If you want to create an " "iterator that will be immediately passed to a function you can write::" msgstr "" #: ../Doc/howto/functional.rst:384 msgid "" "The ``for...in`` clauses contain the sequences to be iterated over. The " "sequences do not have to be the same length, because they are iterated over " "from left to right, **not** in parallel. For each element in ``sequence1``, " "``sequence2`` is looped over from the beginning. ``sequence3`` is then " "looped over for each resulting pair of elements from ``sequence1`` and " "``sequence2``." msgstr "" #: ../Doc/howto/functional.rst:390 msgid "" "To put it another way, a list comprehension or generator expression is " "equivalent to the following Python code::" msgstr "" #: ../Doc/howto/functional.rst:407 msgid "" "This means that when there are multiple ``for...in`` clauses but no ``if`` " "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 list is 9 elements long:" msgstr "" #: ../Doc/howto/functional.rst:419 msgid "" "To avoid introducing an ambiguity into Python's grammar, if ``expression`` " "is creating a tuple, it must be surrounded with parentheses. The first list " "comprehension below is a syntax error, while the second one is correct::" msgstr "" #: ../Doc/howto/functional.rst:430 msgid "Generators" msgstr "Générateurs" #: ../Doc/howto/functional.rst:432 msgid "" "Generators are a special class of functions that simplify the task of " "writing iterators. Regular functions compute a value and return it, but " "generators return an iterator that returns a stream of values." msgstr "" #: ../Doc/howto/functional.rst:436 msgid "" "You're doubtless familiar with how regular function calls work in Python or " "C. When you call a function, it gets a private namespace where its local " "variables are created. When the function reaches a ``return`` statement, " "the local variables are destroyed and the value is returned to the caller. " "A later call to the same function creates a new private namespace and a " "fresh set of local variables. But, what if the local variables weren't " "thrown away on exiting a function? What if you could later resume the " "function where it left off? This is what generators provide; they can be " "thought of as resumable functions." msgstr "" #: ../Doc/howto/functional.rst:445 msgid "Here's the simplest example of a generator function:" msgstr "" #: ../Doc/howto/functional.rst:451 msgid "" "Any function containing a :keyword:`yield` keyword is a generator function; " "this is detected by Python's :term:`bytecode` compiler which compiles the " "function specially as a result." msgstr "" #: ../Doc/howto/functional.rst:455 msgid "" "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 the ``yield`` expression, the generator outputs the value of " "``i``, similar to a ``return`` statement. The big difference between " "``yield`` and a ``return`` 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 generator's :meth:`~generator.__next__` " "method, the function will resume executing." msgstr "" #: ../Doc/howto/functional.rst:464 msgid "Here's a sample usage of the ``generate_ints()`` generator:" msgstr "" #: ../Doc/howto/functional.rst:481 msgid "" "You could equally write ``for i in generate_ints(5)``, or ``a,b,c = " "generate_ints(3)``." msgstr "" #: ../Doc/howto/functional.rst:484 msgid "" "Inside a generator function, ``return value`` causes " "``StopIteration(value)`` to be raised from the :meth:`~generator.__next__` " "method. Once this happens, or the bottom of the function is reached, the " "procession of values ends and the generator cannot yield any further values." msgstr "" #: ../Doc/howto/functional.rst:489 msgid "" "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 example, returning a list of integers could be done by " "setting ``self.count`` to 0, and having the :meth:`~iterator.__next__` " "method increment ``self.count`` and return it. However, for a moderately " "complicated generator, writing a corresponding class can be much messier." msgstr "" #: ../Doc/howto/functional.rst:497 msgid "" "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 in-order traversal of a tree using " "generators recursively. ::" msgstr "" #: ../Doc/howto/functional.rst:513 msgid "" "Two other examples in ``test_generators.py`` produce solutions for the N-" "Queens problem (placing N queens on an NxN chess board so that no queen " "threatens another) and the Knight's Tour (finding a route that takes a " "knight to every square of an NxN chessboard without visiting any square " "twice)." msgstr "" #: ../Doc/howto/functional.rst:521 msgid "Passing values into a generator" msgstr "" #: ../Doc/howto/functional.rst:523 msgid "" "In Python 2.4 and earlier, generators only produced output. Once a " "generator's code was invoked to create an iterator, there was no way to pass " "any new information into the function when its execution is resumed. You " "could hack together this ability by making the generator look at a global " "variable or by passing in some mutable object that callers then modify, but " "these approaches are messy." msgstr "" #: ../Doc/howto/functional.rst:530 msgid "" "In Python 2.5 there's a simple way to pass values into a generator. :keyword:" "`yield` became an expression, returning a value that can be assigned to a " "variable or otherwise operated on::" msgstr "" #: ../Doc/howto/functional.rst:536 msgid "" "I recommend that you **always** put parentheses around a ``yield`` " "expression 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 instead of having to remember when they're needed." msgstr "" #: ../Doc/howto/functional.rst:541 msgid "" "(: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 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) + 12``.)" msgstr "" #: ../Doc/howto/functional.rst:547 msgid "" "Values are sent into a generator by calling its :meth:`send(value) " "` method. This method resumes the generator's code and the " "``yield`` expression returns the specified value. If the regular :meth:" "`~generator.__next__` method is called, the ``yield`` returns ``None``." msgstr "" #: ../Doc/howto/functional.rst:552 msgid "" "Here's a simple counter that increments by 1 and allows changing the value " "of the internal counter." msgstr "" #: ../Doc/howto/functional.rst:567 msgid "And here's an example of changing the counter:" msgstr "" #: ../Doc/howto/functional.rst:584 msgid "" "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 :meth:`~generator.send` method will be the only method used to " "resume your generator function." msgstr "" #: ../Doc/howto/functional.rst:589 msgid "" "In addition to :meth:`~generator.send`, there are two other methods on " "generators:" msgstr "" #: ../Doc/howto/functional.rst:592 msgid "" ":meth:`throw(type, value=None, traceback=None) ` is used to " "raise an exception inside the generator; the exception is raised by the " "``yield`` expression where the generator's execution is paused." msgstr "" #: ../Doc/howto/functional.rst:596 msgid "" ":meth:`~generator.close` raises a :exc:`GeneratorExit` exception inside the " "generator to terminate the iteration. On receiving this exception, the " "generator's code must either raise :exc:`GeneratorExit` or :exc:" "`StopIteration`; catching the exception and doing anything else is illegal " "and will trigger a :exc:`RuntimeError`. :meth:`~generator.close` will also " "be called by Python's garbage collector when the generator is garbage-" "collected." msgstr "" #: ../Doc/howto/functional.rst:604 msgid "" "If you need to run cleanup code when a :exc:`GeneratorExit` occurs, I " "suggest using a ``try: ... finally:`` suite instead of catching :exc:" "`GeneratorExit`." msgstr "" #: ../Doc/howto/functional.rst:607 msgid "" "The cumulative effect of these changes is to turn generators from one-way " "producers of information into both producers and consumers." msgstr "" #: ../Doc/howto/functional.rst:610 msgid "" "Generators also become **coroutines**, a more generalized form of " "subroutines. Subroutines are entered at one point and exited at another " "point (the top of the function, and a ``return`` statement), but coroutines " "can be entered, exited, and resumed at many different points (the ``yield`` " "statements)." msgstr "" #: ../Doc/howto/functional.rst:617 msgid "Built-in functions" msgstr "Fonctions natives" #: ../Doc/howto/functional.rst:619 msgid "" "Let's look in more detail at built-in functions often used with iterators." msgstr "" #: ../Doc/howto/functional.rst:621 msgid "" "Two of Python's built-in functions, :func:`map` and :func:`filter` duplicate " "the features of generator expressions:" msgstr "" #: ../Doc/howto/functional.rst:633 msgid "" ":func:`map(f, iterA, iterB, ...) ` returns an iterator over the sequence" msgstr "" #: ../Doc/howto/functional.rst:625 msgid "" "``f(iterA[0], iterB[0]), f(iterA[1], iterB[1]), f(iterA[2], iterB[2]), ...``." msgstr "" #: ../Doc/howto/functional.rst:635 msgid "You can of course achieve the same effect with a list comprehension." msgstr "" #: ../Doc/howto/functional.rst:637 msgid "" ":func:`filter(predicate, iter) ` returns an iterator over all the " "sequence elements that meet a certain condition, and is similarly duplicated " "by list comprehensions. A **predicate** is a function that returns the " "truth value of some condition; for use with :func:`filter`, the predicate " "must take a single value." msgstr "" #: ../Doc/howto/functional.rst:650 msgid "This can also be written as a list comprehension:" msgstr "" #: ../Doc/howto/functional.rst:656 msgid "" ":func:`enumerate(iter, start=0) ` counts off the elements in the " "iterable returning 2-tuples containing the count (from *start*) and each " "element. ::" msgstr "" #: ../Doc/howto/functional.rst:666 msgid "" ":func:`enumerate` is often used when looping through a list and recording " "the indexes at which certain conditions are met::" msgstr "" #: ../Doc/howto/functional.rst:674 msgid "" ":func:`sorted(iterable, key=None, reverse=False) ` collects all the " "elements of the iterable into a list, sorts the list, and returns the sorted " "result. The *key* and *reverse* arguments are passed through to the " "constructed list's :meth:`~list.sort` method. ::" msgstr "" #: ../Doc/howto/functional.rst:689 msgid "" "(For a more detailed discussion of sorting, see the :ref:`sortinghowto`.)" msgstr "" #: ../Doc/howto/functional.rst:692 msgid "" "The :func:`any(iter) ` and :func:`all(iter) ` built-ins look at " "the truth values of an iterable's contents. :func:`any` returns ``True`` if " "any element in the iterable is a true value, and :func:`all` returns " "``True`` if all of the elements are true values:" msgstr "" #: ../Doc/howto/functional.rst:711 msgid "" ":func:`zip(iterA, iterB, ...) ` takes one element from each iterable " "and returns them in a tuple::" msgstr "" #: ../Doc/howto/functional.rst:717 msgid "" "It 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 `__.)" msgstr "" #: ../Doc/howto/functional.rst:722 msgid "" "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. ::" msgstr "" #: ../Doc/howto/functional.rst:729 msgid "" "You should avoid doing this, though, because an element may be taken from " "the longer iterators and discarded. This means you can't go on to use the " "iterators further because you risk skipping a discarded element." msgstr "" #: ../Doc/howto/functional.rst:735 msgid "The itertools module" msgstr "" #: ../Doc/howto/functional.rst:737 msgid "" "The :mod:`itertools` module contains a number of commonly-used iterators as " "well as functions for combining several iterators. This section will " "introduce the module's contents by showing small examples." msgstr "" #: ../Doc/howto/functional.rst:741 msgid "The module's functions fall into a few broad classes:" msgstr "" #: ../Doc/howto/functional.rst:743 msgid "Functions that create a new iterator based on an existing iterator." msgstr "" #: ../Doc/howto/functional.rst:744 msgid "Functions for treating an iterator's elements as function arguments." msgstr "" #: ../Doc/howto/functional.rst:745 msgid "Functions for selecting portions of an iterator's output." msgstr "" #: ../Doc/howto/functional.rst:746 msgid "A function for grouping an iterator's output." msgstr "" #: ../Doc/howto/functional.rst:749 msgid "Creating new iterators" msgstr "" #: ../Doc/howto/functional.rst:751 msgid "" ":func:`itertools.count(start, step) ` returns an infinite " "stream of evenly spaced values. You can optionally supply the starting " "number, which defaults to 0, and the interval between numbers, which " "defaults to 1::" msgstr "" #: ../Doc/howto/functional.rst:762 msgid "" ":func:`itertools.cycle(iter) ` saves a copy of the contents " "of a provided iterable and returns a new iterator that returns its elements " "from first to last. The new iterator will repeat these elements " "infinitely. ::" msgstr "" #: ../Doc/howto/functional.rst:769 msgid "" ":func:`itertools.repeat(elem, [n]) ` returns the provided " "element *n* times, or returns the element endlessly if *n* is not " "provided. ::" msgstr "" #: ../Doc/howto/functional.rst:777 msgid "" ":func:`itertools.chain(iterA, iterB, ...) ` takes an " "arbitrary number of iterables as input, and returns all the elements of the " "first iterator, then all the elements of the second, and so on, until all of " "the iterables have been exhausted. ::" msgstr "" #: ../Doc/howto/functional.rst:785 msgid "" ":func:`itertools.islice(iter, [start], stop, [step]) ` " "returns a stream that's a slice of the iterator. With a single *stop* " "argument, it will return the first *stop* elements. If you supply a " "starting index, you'll get *stop-start* elements, and if you supply a value " "for *step*, elements will be skipped accordingly. Unlike Python's string " "and list slicing, you can't use negative values for *start*, *stop*, or " "*step*. ::" msgstr "" #: ../Doc/howto/functional.rst:799 msgid "" ":func:`itertools.tee(iter, [n]) ` replicates an iterator; it " "returns *n* independent iterators that will all return the contents of the " "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 significant memory if the iterator is large " "and one of the new iterators is consumed more than the others. ::" msgstr "" #: ../Doc/howto/functional.rst:818 msgid "Calling functions on elements" msgstr "" #: ../Doc/howto/functional.rst:820 msgid "" "The :mod:`operator` module contains a set of functions corresponding to " "Python's operators. Some examples are :func:`operator.add(a, b) ` (adds two values), :func:`operator.ne(a, b) ` (same as " "``a != b``), and :func:`operator.attrgetter('id') ` " "(returns a callable that fetches the ``.id`` attribute)." msgstr "" #: ../Doc/howto/functional.rst:826 msgid "" ":func:`itertools.starmap(func, iter) ` assumes that the " "iterable will return a stream of tuples, and calls *func* using these tuples " "as the arguments::" msgstr "" #: ../Doc/howto/functional.rst:838 msgid "Selecting elements" msgstr "" #: ../Doc/howto/functional.rst:840 msgid "" "Another group of functions chooses a subset of an iterator's elements based " "on a predicate." msgstr "" #: ../Doc/howto/functional.rst:843 msgid "" ":func:`itertools.filterfalse(predicate, iter) ` is " "the opposite of :func:`filter`, returning all elements for which the " "predicate returns false::" msgstr "" #: ../Doc/howto/functional.rst:850 msgid "" ":func:`itertools.takewhile(predicate, iter) ` returns " "elements for as long as the predicate returns true. Once the predicate " "returns false, the iterator will signal the end of its results. ::" msgstr "" #: ../Doc/howto/functional.rst:863 msgid "" ":func:`itertools.dropwhile(predicate, iter) ` discards " "elements while the predicate returns true, and then returns the rest of the " "iterable's results. ::" msgstr "" #: ../Doc/howto/functional.rst:873 msgid "" ":func:`itertools.compress(data, selectors) ` takes two " "iterators and returns only those elements of *data* for which the " "corresponding element of *selectors* is true, stopping whenever either one " "is exhausted::" msgstr "" #: ../Doc/howto/functional.rst:882 msgid "Combinatoric functions" msgstr "" #: ../Doc/howto/functional.rst:884 msgid "" "The :func:`itertools.combinations(iterable, r) ` " "returns an iterator giving all possible *r*-tuple combinations of the " "elements contained in *iterable*. ::" msgstr "" #: ../Doc/howto/functional.rst:899 msgid "" "The elements within each tuple remain in the same order as *iterable* " "returned them. For example, the number 1 is always before 2, 3, 4, or 5 in " "the examples above. A similar function, :func:`itertools." "permutations(iterable, r=None) `, removes this " "constraint on the order, returning all possible arrangements of length *r*::" msgstr "" #: ../Doc/howto/functional.rst:918 msgid "" "If you don't supply a value for *r* the length of the iterable is used, " "meaning that all the elements are permuted." msgstr "" #: ../Doc/howto/functional.rst:921 msgid "" "Note that these functions produce all of the possible combinations by " "position and don't require that the contents of *iterable* are unique::" msgstr "" #: ../Doc/howto/functional.rst:928 msgid "" "The identical tuple ``('a', 'a', 'b')`` occurs twice, but the two 'a' " "strings came from different positions." msgstr "" #: ../Doc/howto/functional.rst:931 msgid "" "The :func:`itertools.combinations_with_replacement(iterable, r) ` function relaxes a different constraint: " "elements can be repeated within a single tuple. Conceptually an element is " "selected for the first position of each tuple and then is replaced before " "the second element is selected. ::" msgstr "" #: ../Doc/howto/functional.rst:946 msgid "Grouping elements" msgstr "" #: ../Doc/howto/functional.rst:948 msgid "" "The last function I'll discuss, :func:`itertools.groupby(iter, " "key_func=None) `, is the most complicated. " "``key_func(elem)`` is a function that can compute a key value for each " "element returned by the iterable. If you don't supply a key function, the " "key is simply each element itself." msgstr "" #: ../Doc/howto/functional.rst:953 msgid "" ":func:`~itertools.groupby` collects all the consecutive elements from the " "underlying iterable that have the same key value, and returns a stream of 2-" "tuples containing a key value and an iterator for the elements with that key." msgstr "" #: ../Doc/howto/functional.rst:981 msgid "" ":func:`~itertools.groupby` assumes that the underlying iterable's contents " "will already be sorted based on the key. Note that the returned iterators " "also use the underlying iterable, so you have to consume the results of " "iterator-1 before requesting iterator-2 and its corresponding key." msgstr "" #: ../Doc/howto/functional.rst:988 msgid "The functools module" msgstr "" #: ../Doc/howto/functional.rst:990 msgid "" "The :mod:`functools` module in Python 2.5 contains some higher-order " "functions. A **higher-order function** takes one or more functions as input " "and returns a new function. The most useful tool in this module is the :" "func:`functools.partial` function." msgstr "" #: ../Doc/howto/functional.rst:995 msgid "" "For programs written in a functional style, you'll sometimes want to " "construct variants of existing functions that have some of the parameters " "filled in. 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 one of ``f()``'s parameters. This is called " "\"partial function application\"." msgstr "" #: ../Doc/howto/functional.rst:1001 msgid "" "The constructor for :func:`~functools.partial` takes the arguments " "``(function, arg1, arg2, ..., kwarg1=value1, kwarg2=value2)``. The " "resulting object is callable, so you can just call it to invoke ``function`` " "with the filled-in arguments." msgstr "" #: ../Doc/howto/functional.rst:1006 msgid "Here's a small but realistic example::" msgstr "Voici un exemple court mais réaliste ::" #: ../Doc/howto/functional.rst:1018 msgid "" ":func:`functools.reduce(func, iter, [initial_value]) ` " "cumulatively performs an operation on all the iterable's elements and, " "therefore, can't be applied to infinite iterables. *func* must be a function " "that takes two elements and returns a single value. :func:`functools." "reduce` takes the first two elements A and B returned by the iterator and " "calculates ``func(A, B)``. It then requests the third element, C, " "calculates ``func(func(A, B), C)``, combines this result with the fourth " "element returned, and continues until the iterable is exhausted. If the " "iterable returns no values at all, a :exc:`TypeError` exception is raised. " "If the initial value is supplied, it's used as a starting point and " "``func(initial_value, A)`` is the first calculation. ::" msgstr "" #: ../Doc/howto/functional.rst:1042 msgid "" "If you use :func:`operator.add` with :func:`functools.reduce`, you'll add up " "all the elements of the iterable. This case is so common that there's a " "special built-in called :func:`sum` to compute it:" msgstr "" #: ../Doc/howto/functional.rst:1054 msgid "" "For many uses of :func:`functools.reduce`, though, it can be clearer to just " "write the obvious :keyword:`for` loop::" msgstr "" #: ../Doc/howto/functional.rst:1066 msgid "" "A related function is :func:`itertools.accumulate(iterable, func=operator." "add) `. It performs the same calculation, but instead " "of returning only the final result, :func:`accumulate` returns an iterator " "that also yields each partial result::" msgstr "" #: ../Doc/howto/functional.rst:1079 msgid "The operator module" msgstr "" #: ../Doc/howto/functional.rst:1081 msgid "" "The :mod:`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." msgstr "" #: ../Doc/howto/functional.rst:1086 msgid "Some of the functions in this module are:" msgstr "" #: ../Doc/howto/functional.rst:1088 msgid "" "Math operations: ``add()``, ``sub()``, ``mul()``, ``floordiv()``, " "``abs()``, ..." msgstr "" #: ../Doc/howto/functional.rst:1089 msgid "Logical operations: ``not_()``, ``truth()``." msgstr "" #: ../Doc/howto/functional.rst:1090 msgid "Bitwise operations: ``and_()``, ``or_()``, ``invert()``." msgstr "" #: ../Doc/howto/functional.rst:1091 msgid "" "Comparisons: ``eq()``, ``ne()``, ``lt()``, ``le()``, ``gt()``, and ``ge()``." msgstr "" #: ../Doc/howto/functional.rst:1092 msgid "Object identity: ``is_()``, ``is_not()``." msgstr "" #: ../Doc/howto/functional.rst:1094 msgid "Consult the operator module's documentation for a complete list." msgstr "" #: ../Doc/howto/functional.rst:1098 msgid "Small functions and the lambda expression" msgstr "" #: ../Doc/howto/functional.rst:1100 msgid "" "When writing functional-style programs, you'll often need little functions " "that act as predicates or that combine elements in some way." msgstr "" #: ../Doc/howto/functional.rst:1103 msgid "" "If there's a Python built-in or a module function that's suitable, you don't " "need to define a new function at all::" msgstr "" #: ../Doc/howto/functional.rst:1109 msgid "" "If the function you need doesn't exist, you need to write it. One way to " "write small functions is to use the :keyword:`lambda` statement. ``lambda`` " "takes a number of parameters and an expression combining these parameters, " "and creates an anonymous function that returns the value of the expression::" msgstr "" #: ../Doc/howto/functional.rst:1118 msgid "" "An alternative is to just use the ``def`` statement and define a function in " "the usual way::" msgstr "" #: ../Doc/howto/functional.rst:1127 msgid "" "Which alternative is preferable? That's a style question; my usual course " "is to avoid using ``lambda``." msgstr "" #: ../Doc/howto/functional.rst:1130 msgid "" "One reason for my preference is that ``lambda`` is quite limited in the " "functions it can define. The result has to be computable as a single " "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 " "``lambda`` statement, you'll end up with an overly complicated expression " "that's hard to read. Quick, what's the following code doing? ::" msgstr "" #: ../Doc/howto/functional.rst:1140 msgid "" "You can figure it out, but it takes time to disentangle the expression to " "figure out what's going on. Using a short nested ``def`` statements makes " "things a little bit better::" msgstr "" #: ../Doc/howto/functional.rst:1150 msgid "But it would be best of all if I had simply used a ``for`` loop::" msgstr "" #: ../Doc/howto/functional.rst:1156 msgid "Or the :func:`sum` built-in and a generator expression::" msgstr "" #: ../Doc/howto/functional.rst:1160 msgid "" "Many uses of :func:`functools.reduce` are clearer when written as ``for`` " "loops." msgstr "" #: ../Doc/howto/functional.rst:1162 msgid "" "Fredrik Lundh once suggested the following set of rules for refactoring uses " "of ``lambda``:" msgstr "" #: ../Doc/howto/functional.rst:1165 msgid "Write a lambda function." msgstr "" #: ../Doc/howto/functional.rst:1166 msgid "Write a comment explaining what the heck that lambda does." msgstr "" #: ../Doc/howto/functional.rst:1167 msgid "" "Study the comment for a while, and think of a name that captures the essence " "of the comment." msgstr "" #: ../Doc/howto/functional.rst:1169 msgid "Convert the lambda to a def statement, using that name." msgstr "" #: ../Doc/howto/functional.rst:1170 msgid "Remove the comment." msgstr "" #: ../Doc/howto/functional.rst:1172 msgid "" "I really like these rules, but you're free to disagree about whether this " "lambda-free style is better." msgstr "" #: ../Doc/howto/functional.rst:1177 msgid "Revision History and Acknowledgements" msgstr "" #: ../Doc/howto/functional.rst:1179 msgid "" "The author would like to thank the following people for offering " "suggestions, corrections and assistance with various drafts of this article: " "Ian Bicking, Nick Coghlan, Nick Efford, Raymond Hettinger, Jim Jewett, Mike " "Krell, Leandro Lameiro, Jussi Salmela, Collin Winter, Blake Winton." msgstr "" #: ../Doc/howto/functional.rst:1184 msgid "Version 0.1: posted June 30 2006." msgstr "" #: ../Doc/howto/functional.rst:1186 msgid "Version 0.11: posted July 1 2006. Typo fixes." msgstr "" #: ../Doc/howto/functional.rst:1188 msgid "" "Version 0.2: posted July 10 2006. Merged genexp and listcomp sections into " "one. Typo fixes." msgstr "" #: ../Doc/howto/functional.rst:1191 msgid "" "Version 0.21: Added more references suggested on the tutor mailing list." msgstr "" #: ../Doc/howto/functional.rst:1193 msgid "" "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." msgstr "" #: ../Doc/howto/functional.rst:1198 msgid "References" msgstr "Références" #: ../Doc/howto/functional.rst:1201 msgid "General" msgstr "" #: ../Doc/howto/functional.rst:1203 msgid "" "**Structure and Interpretation of Computer Programs**, by Harold Abelson and " "Gerald Jay Sussman with Julie Sussman. Full text at https://mitpress.mit." "edu/sicp/. In this classic textbook of computer science, chapters 2 and 3 " "discuss the use of sequences and streams to organize the data flow inside a " "program. The book uses Scheme for its examples, but many of the design " "approaches described in these chapters are applicable to functional-style " "Python code." msgstr "" #: ../Doc/howto/functional.rst:1211 msgid "" "http://www.defmacro.org/ramblings/fp.html: A general introduction to " "functional programming that uses Java examples and has a lengthy historical " "introduction." msgstr "" #: ../Doc/howto/functional.rst:1214 msgid "" "https://en.wikipedia.org/wiki/Functional_programming: General Wikipedia " "entry describing functional programming." msgstr "" #: ../Doc/howto/functional.rst:1217 msgid "https://en.wikipedia.org/wiki/Coroutine: Entry for coroutines." msgstr "" #: ../Doc/howto/functional.rst:1219 msgid "" "https://en.wikipedia.org/wiki/Currying: Entry for the concept of currying." msgstr "" #: ../Doc/howto/functional.rst:1222 msgid "Python-specific" msgstr "" #: ../Doc/howto/functional.rst:1224 msgid "" "http://gnosis.cx/TPiP/: The first chapter of David Mertz's book :title-" "reference:`Text Processing in Python` discusses functional programming for " "text processing, in the section titled \"Utilizing Higher-Order Functions in " "Text Processing\"." msgstr "" #: ../Doc/howto/functional.rst:1229 msgid "" "Mertz also wrote a 3-part series of articles on functional programming for " "IBM's DeveloperWorks site; see `part 1 `__, `part 2 `__, and `part 3 `__," msgstr "" #: ../Doc/howto/functional.rst:1237 msgid "Python documentation" msgstr "" #: ../Doc/howto/functional.rst:1239 msgid "Documentation for the :mod:`itertools` module." msgstr "" #: ../Doc/howto/functional.rst:1241 msgid "Documentation for the :mod:`functools` module." msgstr "" #: ../Doc/howto/functional.rst:1243 msgid "Documentation for the :mod:`operator` module." msgstr "" #: ../Doc/howto/functional.rst:1245 msgid ":pep:`289`: \"Generator Expressions\"" msgstr "" #: ../Doc/howto/functional.rst:1247 msgid "" ":pep:`342`: \"Coroutines via Enhanced Generators\" describes the new " "generator features in Python 2.5." msgstr ""