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1277 lines (1054 loc) · 49.9 KB
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# SOME DESCRIPTIVE TITLE.
# Copyright (C) 2001-2025, Python Software Foundation
# This file is distributed under the same license as the Python package.
# FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
#
#, fuzzy
msgid ""
msgstr ""
"Project-Id-Version: Python 3.13\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2025-02-10 02:51+0330\n"
"PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
"Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
"Language-Team: LANGUAGE <LL@li.org>\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
#: tutorial/controlflow.rst:5
msgid "More Control Flow Tools"
msgstr ""
#: tutorial/controlflow.rst:7
msgid "As well as the :keyword:`while` statement just introduced, Python uses a few more that we will encounter in this chapter."
msgstr ""
#: tutorial/controlflow.rst:14
msgid ":keyword:`!if` Statements"
msgstr ""
#: tutorial/controlflow.rst:16
msgid "Perhaps the most well-known statement type is the :keyword:`if` statement. For example::"
msgstr ""
#: tutorial/controlflow.rst:19
msgid ">>> x = int(input(\"Please enter an integer: \"))\n"
"Please enter an integer: 42\n"
">>> if x < 0:\n"
"... x = 0\n"
"... print('Negative changed to zero')\n"
"... elif x == 0:\n"
"... print('Zero')\n"
"... elif x == 1:\n"
"... print('Single')\n"
"... else:\n"
"... print('More')\n"
"...\n"
"More"
msgstr ""
#: tutorial/controlflow.rst:33
msgid "There can be zero or more :keyword:`elif` parts, and the :keyword:`else` part is optional. The keyword ':keyword:`!elif`' is short for 'else if', and is useful to avoid excessive indentation. An :keyword:`!if` ... :keyword:`!elif` ... :keyword:`!elif` ... sequence is a substitute for the ``switch`` or ``case`` statements found in other languages."
msgstr ""
#: tutorial/controlflow.rst:39
msgid "If you're comparing the same value to several constants, or checking for specific types or attributes, you may also find the :keyword:`!match` statement useful. For more details see :ref:`tut-match`."
msgstr ""
#: tutorial/controlflow.rst:46
msgid ":keyword:`!for` Statements"
msgstr ""
#: tutorial/controlflow.rst:51
msgid "The :keyword:`for` statement in Python differs a bit from what you may be used to in C or Pascal. Rather than always iterating over an arithmetic progression of numbers (like in Pascal), or giving the user the ability to define both the iteration step and halting condition (as C), Python's :keyword:`!for` statement iterates over the items of any sequence (a list or a string), in the order that they appear in the sequence. For example (no pun intended):"
msgstr ""
#: tutorial/controlflow.rst:63
msgid ">>> # Measure some strings:\n"
">>> words = ['cat', 'window', 'defenestrate']\n"
">>> for w in words:\n"
"... print(w, len(w))\n"
"...\n"
"cat 3\n"
"window 6\n"
"defenestrate 12"
msgstr ""
#: tutorial/controlflow.rst:72
msgid "Code that modifies a collection while iterating over that same collection can be tricky to get right. Instead, it is usually more straight-forward to loop over a copy of the collection or to create a new collection::"
msgstr ""
#: tutorial/controlflow.rst:76
msgid "# Create a sample collection\n"
"users = {'Hans': 'active', 'Éléonore': 'inactive', '景太郎': 'active'}\n"
"\n"
"# Strategy: Iterate over a copy\n"
"for user, status in users.copy().items():\n"
" if status == 'inactive':\n"
" del users[user]\n"
"\n"
"# Strategy: Create a new collection\n"
"active_users = {}\n"
"for user, status in users.items():\n"
" if status == 'active':\n"
" active_users[user] = status"
msgstr ""
#: tutorial/controlflow.rst:94
msgid "The :func:`range` Function"
msgstr ""
#: tutorial/controlflow.rst:96
msgid "If you do need to iterate over a sequence of numbers, the built-in function :func:`range` comes in handy. It generates arithmetic progressions::"
msgstr ""
#: tutorial/controlflow.rst:99
msgid ">>> for i in range(5):\n"
"... print(i)\n"
"...\n"
"0\n"
"1\n"
"2\n"
"3\n"
"4"
msgstr ""
#: tutorial/controlflow.rst:108
msgid "The given end point is never part of the generated sequence; ``range(10)`` generates 10 values, the legal indices for items of a sequence of length 10. It is possible to let the range start at another number, or to specify a different increment (even negative; sometimes this is called the 'step')::"
msgstr ""
#: tutorial/controlflow.rst:113
msgid ">>> list(range(5, 10))\n"
"[5, 6, 7, 8, 9]\n"
"\n"
">>> list(range(0, 10, 3))\n"
"[0, 3, 6, 9]\n"
"\n"
">>> list(range(-10, -100, -30))\n"
"[-10, -40, -70]"
msgstr ""
#: tutorial/controlflow.rst:122
msgid "To iterate over the indices of a sequence, you can combine :func:`range` and :func:`len` as follows::"
msgstr ""
#: tutorial/controlflow.rst:125
msgid ">>> a = ['Mary', 'had', 'a', 'little', 'lamb']\n"
">>> for i in range(len(a)):\n"
"... print(i, a[i])\n"
"...\n"
"0 Mary\n"
"1 had\n"
"2 a\n"
"3 little\n"
"4 lamb"
msgstr ""
#: tutorial/controlflow.rst:135
msgid "In most such cases, however, it is convenient to use the :func:`enumerate` function, see :ref:`tut-loopidioms`."
msgstr ""
#: tutorial/controlflow.rst:138
msgid "A strange thing happens if you just print a range::"
msgstr ""
#: tutorial/controlflow.rst:140
msgid ">>> range(10)\n"
"range(0, 10)"
msgstr ""
#: tutorial/controlflow.rst:143
msgid "In many ways the object returned by :func:`range` behaves as if it is a list, but in fact it isn't. It is an object which returns the successive items of the desired sequence when you iterate over it, but it doesn't really make the list, thus saving space."
msgstr ""
#: tutorial/controlflow.rst:148
msgid "We say such an object is :term:`iterable`, that is, suitable as a target for functions and constructs that expect something from which they can obtain successive items until the supply is exhausted. We have seen that the :keyword:`for` statement is such a construct, while an example of a function that takes an iterable is :func:`sum`::"
msgstr ""
#: tutorial/controlflow.rst:154
msgid ">>> sum(range(4)) # 0 + 1 + 2 + 3\n"
"6"
msgstr ""
#: tutorial/controlflow.rst:157
msgid "Later we will see more functions that return iterables and take iterables as arguments. In chapter :ref:`tut-structures`, we will discuss in more detail about :func:`list`."
msgstr ""
#: tutorial/controlflow.rst:164
msgid ":keyword:`!break` and :keyword:`!continue` Statements"
msgstr ""
#: tutorial/controlflow.rst:166
msgid "The :keyword:`break` statement breaks out of the innermost enclosing :keyword:`for` or :keyword:`while` loop::"
msgstr ""
#: tutorial/controlflow.rst:169
msgid ">>> for n in range(2, 10):\n"
"... for x in range(2, n):\n"
"... if n % x == 0:\n"
"... print(f\"{n} equals {x} * {n//x}\")\n"
"... break\n"
"...\n"
"4 equals 2 * 2\n"
"6 equals 2 * 3\n"
"8 equals 2 * 4\n"
"9 equals 3 * 3"
msgstr ""
#: tutorial/controlflow.rst:180
msgid "The :keyword:`continue` statement continues with the next iteration of the loop::"
msgstr ""
#: tutorial/controlflow.rst:183
msgid ">>> for num in range(2, 10):\n"
"... if num % 2 == 0:\n"
"... print(f\"Found an even number {num}\")\n"
"... continue\n"
"... print(f\"Found an odd number {num}\")\n"
"...\n"
"Found an even number 2\n"
"Found an odd number 3\n"
"Found an even number 4\n"
"Found an odd number 5\n"
"Found an even number 6\n"
"Found an odd number 7\n"
"Found an even number 8\n"
"Found an odd number 9"
msgstr ""
#: tutorial/controlflow.rst:202
msgid ":keyword:`!else` Clauses on Loops"
msgstr ""
#: tutorial/controlflow.rst:204
msgid "In a :keyword:`!for` or :keyword:`!while` loop the :keyword:`!break` statement may be paired with an :keyword:`!else` clause. If the loop finishes without executing the :keyword:`!break`, the :keyword:`!else` clause executes."
msgstr ""
#: tutorial/controlflow.rst:208
msgid "In a :keyword:`for` loop, the :keyword:`!else` clause is executed after the loop finishes its final iteration, that is, if no break occurred."
msgstr ""
#: tutorial/controlflow.rst:211
msgid "In a :keyword:`while` loop, it's executed after the loop's condition becomes false."
msgstr ""
#: tutorial/controlflow.rst:213
msgid "In either kind of loop, the :keyword:`!else` clause is **not** executed if the loop was terminated by a :keyword:`break`. Of course, other ways of ending the loop early, such as a :keyword:`return` or a raised exception, will also skip execution of the :keyword:`else` clause."
msgstr ""
#: tutorial/controlflow.rst:218
msgid "This is exemplified in the following :keyword:`!for` loop, which searches for prime numbers::"
msgstr ""
#: tutorial/controlflow.rst:221
msgid ">>> for n in range(2, 10):\n"
"... for x in range(2, n):\n"
"... if n % x == 0:\n"
"... print(n, 'equals', x, '*', n//x)\n"
"... break\n"
"... else:\n"
"... # loop fell through without finding a factor\n"
"... print(n, 'is a prime number')\n"
"...\n"
"2 is a prime number\n"
"3 is a prime number\n"
"4 equals 2 * 2\n"
"5 is a prime number\n"
"6 equals 2 * 3\n"
"7 is a prime number\n"
"8 equals 2 * 4\n"
"9 equals 3 * 3"
msgstr ""
#: tutorial/controlflow.rst:239
msgid "(Yes, this is the correct code. Look closely: the ``else`` clause belongs to the ``for`` loop, **not** the ``if`` statement.)"
msgstr ""
#: tutorial/controlflow.rst:242
msgid "One way to think of the else clause is to imagine it paired with the ``if`` inside the loop. As the loop executes, it will run a sequence like if/if/if/else. The ``if`` is inside the loop, encountered a number of times. If the condition is ever true, a ``break`` will happen. If the condition is never true, the ``else`` clause outside the loop will execute."
msgstr ""
#: tutorial/controlflow.rst:248
msgid "When used with a loop, the ``else`` clause has more in common with the ``else`` clause of a :keyword:`try` statement than it does with that of ``if`` statements: a ``try`` statement's ``else`` clause runs when no exception occurs, and a loop's ``else`` clause runs when no ``break`` occurs. For more on the ``try`` statement and exceptions, see :ref:`tut-handling`."
msgstr ""
#: tutorial/controlflow.rst:257
msgid ":keyword:`!pass` Statements"
msgstr ""
#: tutorial/controlflow.rst:259
msgid "The :keyword:`pass` statement does nothing. It can be used when a statement is required syntactically but the program requires no action. For example::"
msgstr ""
#: tutorial/controlflow.rst:262
msgid ">>> while True:\n"
"... pass # Busy-wait for keyboard interrupt (Ctrl+C)\n"
"..."
msgstr ""
#: tutorial/controlflow.rst:266
msgid "This is commonly used for creating minimal classes::"
msgstr ""
#: tutorial/controlflow.rst:268
msgid ">>> class MyEmptyClass:\n"
"... pass\n"
"..."
msgstr ""
#: tutorial/controlflow.rst:272
msgid "Another place :keyword:`pass` can be used is as a place-holder for a function or conditional body when you are working on new code, allowing you to keep thinking at a more abstract level. The :keyword:`!pass` is silently ignored::"
msgstr ""
#: tutorial/controlflow.rst:276
msgid ">>> def initlog(*args):\n"
"... pass # Remember to implement this!\n"
"..."
msgstr ""
#: tutorial/controlflow.rst:284
msgid ":keyword:`!match` Statements"
msgstr ""
#: tutorial/controlflow.rst:286
msgid "A :keyword:`match` statement takes an expression and compares its value to successive patterns given as one or more case blocks. This is superficially similar to a switch statement in C, Java or JavaScript (and many other languages), but it's more similar to pattern matching in languages like Rust or Haskell. Only the first pattern that matches gets executed and it can also extract components (sequence elements or object attributes) from the value into variables."
msgstr ""
#: tutorial/controlflow.rst:294
msgid "The simplest form compares a subject value against one or more literals::"
msgstr ""
#: tutorial/controlflow.rst:296
msgid "def http_error(status):\n"
" match status:\n"
" case 400:\n"
" return \"Bad request\"\n"
" case 404:\n"
" return \"Not found\"\n"
" case 418:\n"
" return \"I'm a teapot\"\n"
" case _:\n"
" return \"Something's wrong with the internet\""
msgstr ""
#: tutorial/controlflow.rst:307
msgid "Note the last block: the \"variable name\" ``_`` acts as a *wildcard* and never fails to match. If no case matches, none of the branches is executed."
msgstr ""
#: tutorial/controlflow.rst:310
msgid "You can combine several literals in a single pattern using ``|`` (\"or\")::"
msgstr ""
#: tutorial/controlflow.rst:312
msgid "case 401 | 403 | 404:\n"
" return \"Not allowed\""
msgstr ""
#: tutorial/controlflow.rst:315
msgid "Patterns can look like unpacking assignments, and can be used to bind variables::"
msgstr ""
#: tutorial/controlflow.rst:318
msgid "# point is an (x, y) tuple\n"
"match point:\n"
" case (0, 0):\n"
" print(\"Origin\")\n"
" case (0, y):\n"
" print(f\"Y={y}\")\n"
" case (x, 0):\n"
" print(f\"X={x}\")\n"
" case (x, y):\n"
" print(f\"X={x}, Y={y}\")\n"
" case _:\n"
" raise ValueError(\"Not a point\")"
msgstr ""
#: tutorial/controlflow.rst:331
msgid "Study that one carefully! The first pattern has two literals, and can be thought of as an extension of the literal pattern shown above. But the next two patterns combine a literal and a variable, and the variable *binds* a value from the subject (``point``). The fourth pattern captures two values, which makes it conceptually similar to the unpacking assignment ``(x, y) = point``."
msgstr ""
#: tutorial/controlflow.rst:338
msgid "If you are using classes to structure your data you can use the class name followed by an argument list resembling a constructor, but with the ability to capture attributes into variables::"
msgstr ""
#: tutorial/controlflow.rst:342
msgid "class Point:\n"
" def __init__(self, x, y):\n"
" self.x = x\n"
" self.y = y\n"
"\n"
"def where_is(point):\n"
" match point:\n"
" case Point(x=0, y=0):\n"
" print(\"Origin\")\n"
" case Point(x=0, y=y):\n"
" print(f\"Y={y}\")\n"
" case Point(x=x, y=0):\n"
" print(f\"X={x}\")\n"
" case Point():\n"
" print(\"Somewhere else\")\n"
" case _:\n"
" print(\"Not a point\")"
msgstr ""
#: tutorial/controlflow.rst:360
msgid "You can use positional parameters with some builtin classes that provide an ordering for their attributes (e.g. dataclasses). You can also define a specific position for attributes in patterns by setting the ``__match_args__`` special attribute in your classes. If it's set to (\"x\", \"y\"), the following patterns are all equivalent (and all bind the ``y`` attribute to the ``var`` variable)::"
msgstr ""
#: tutorial/controlflow.rst:366
msgid "Point(1, var)\n"
"Point(1, y=var)\n"
"Point(x=1, y=var)\n"
"Point(y=var, x=1)"
msgstr ""
#: tutorial/controlflow.rst:371
msgid "A recommended way to read patterns is to look at them as an extended form of what you would put on the left of an assignment, to understand which variables would be set to what. Only the standalone names (like ``var`` above) are assigned to by a match statement. Dotted names (like ``foo.bar``), attribute names (the ``x=`` and ``y=`` above) or class names (recognized by the \"(...)\" next to them like ``Point`` above) are never assigned to."
msgstr ""
#: tutorial/controlflow.rst:378
msgid "Patterns can be arbitrarily nested. For example, if we have a short list of Points, with ``__match_args__`` added, we could match it like this::"
msgstr ""
#: tutorial/controlflow.rst:381
msgid "class Point:\n"
" __match_args__ = ('x', 'y')\n"
" def __init__(self, x, y):\n"
" self.x = x\n"
" self.y = y\n"
"\n"
"match points:\n"
" case []:\n"
" print(\"No points\")\n"
" case [Point(0, 0)]:\n"
" print(\"The origin\")\n"
" case [Point(x, y)]:\n"
" print(f\"Single point {x}, {y}\")\n"
" case [Point(0, y1), Point(0, y2)]:\n"
" print(f\"Two on the Y axis at {y1}, {y2}\")\n"
" case _:\n"
" print(\"Something else\")"
msgstr ""
#: tutorial/controlflow.rst:399
msgid "We can add an ``if`` clause to a pattern, known as a \"guard\". If the guard is false, ``match`` goes on to try the next case block. Note that value capture happens before the guard is evaluated::"
msgstr ""
#: tutorial/controlflow.rst:403
msgid "match point:\n"
" case Point(x, y) if x == y:\n"
" print(f\"Y=X at {x}\")\n"
" case Point(x, y):\n"
" print(f\"Not on the diagonal\")"
msgstr ""
#: tutorial/controlflow.rst:409
msgid "Several other key features of this statement:"
msgstr ""
#: tutorial/controlflow.rst:411
msgid "Like unpacking assignments, tuple and list patterns have exactly the same meaning and actually match arbitrary sequences. An important exception is that they don't match iterators or strings."
msgstr ""
#: tutorial/controlflow.rst:415
msgid "Sequence patterns support extended unpacking: ``[x, y, *rest]`` and ``(x, y, *rest)`` work similar to unpacking assignments. The name after ``*`` may also be ``_``, so ``(x, y, *_)`` matches a sequence of at least two items without binding the remaining items."
msgstr ""
#: tutorial/controlflow.rst:420
msgid "Mapping patterns: ``{\"bandwidth\": b, \"latency\": l}`` captures the ``\"bandwidth\"`` and ``\"latency\"`` values from a dictionary. Unlike sequence patterns, extra keys are ignored. An unpacking like ``**rest`` is also supported. (But ``**_`` would be redundant, so it is not allowed.)"
msgstr ""
#: tutorial/controlflow.rst:425
msgid "Subpatterns may be captured using the ``as`` keyword::"
msgstr ""
#: tutorial/controlflow.rst:427
msgid "case (Point(x1, y1), Point(x2, y2) as p2): ..."
msgstr ""
#: tutorial/controlflow.rst:429
msgid "will capture the second element of the input as ``p2`` (as long as the input is a sequence of two points)"
msgstr ""
#: tutorial/controlflow.rst:432
msgid "Most literals are compared by equality, however the singletons ``True``, ``False`` and ``None`` are compared by identity."
msgstr ""
#: tutorial/controlflow.rst:435
msgid "Patterns may use named constants. These must be dotted names to prevent them from being interpreted as capture variable::"
msgstr ""
#: tutorial/controlflow.rst:438
msgid "from enum import Enum\n"
"class Color(Enum):\n"
" RED = 'red'\n"
" GREEN = 'green'\n"
" BLUE = 'blue'\n"
"\n"
"color = Color(input(\"Enter your choice of 'red', 'blue' or 'green': \"))\n"
"\n"
"match color:\n"
" case Color.RED:\n"
" print(\"I see red!\")\n"
" case Color.GREEN:\n"
" print(\"Grass is green\")\n"
" case Color.BLUE:\n"
" print(\"I'm feeling the blues :(\")"
msgstr ""
#: tutorial/controlflow.rst:454
msgid "For a more detailed explanation and additional examples, you can look into :pep:`636` which is written in a tutorial format."
msgstr ""
#: tutorial/controlflow.rst:460
msgid "Defining Functions"
msgstr ""
#: tutorial/controlflow.rst:462
msgid "We can create a function that writes the Fibonacci series to an arbitrary boundary::"
msgstr ""
#: tutorial/controlflow.rst:465
msgid ">>> def fib(n): # write Fibonacci series less than n\n"
"... \"\"\"Print a Fibonacci series less than n.\"\"\"\n"
"... a, b = 0, 1\n"
"... while a < n:\n"
"... print(a, end=' ')\n"
"... a, b = b, a+b\n"
"... print()\n"
"...\n"
">>> # Now call the function we just defined:\n"
">>> fib(2000)\n"
"0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597"
msgstr ""
#: tutorial/controlflow.rst:482
msgid "The keyword :keyword:`def` introduces a function *definition*. It must be followed by the function name and the parenthesized list of formal parameters. The statements that form the body of the function start at the next line, and must be indented."
msgstr ""
#: tutorial/controlflow.rst:487
msgid "The first statement of the function body can optionally be a string literal; this string literal is the function's documentation string, or :dfn:`docstring`. (More about docstrings can be found in the section :ref:`tut-docstrings`.) There are tools which use docstrings to automatically produce online or printed documentation, or to let the user interactively browse through code; it's good practice to include docstrings in code that you write, so make a habit of it."
msgstr ""
#: tutorial/controlflow.rst:494
msgid "The *execution* of a function introduces a new symbol table used for the local variables of the function. More precisely, all variable assignments in a function store the value in the local symbol table; whereas variable references first look in the local symbol table, then in the local symbol tables of enclosing functions, then in the global symbol table, and finally in the table of built-in names. Thus, global variables and variables of enclosing functions cannot be directly assigned a value within a function (unless, for global variables, named in a :keyword:`global` statement, or, for variables of enclosing functions, named in a :keyword:`nonlocal` statement), although they may be referenced."
msgstr ""
#: tutorial/controlflow.rst:505
msgid "The actual parameters (arguments) to a function call are introduced in the local symbol table of the called function when it is called; thus, arguments are passed using *call by value* (where the *value* is always an object *reference*, not the value of the object). [#]_ When a function calls another function, or calls itself recursively, a new local symbol table is created for that call."
msgstr ""
#: tutorial/controlflow.rst:512
msgid "A function definition associates the function name with the function object in the current symbol table. The interpreter recognizes the object pointed to by that name as a user-defined function. Other names can also point to that same function object and can also be used to access the function::"
msgstr ""
#: tutorial/controlflow.rst:517
msgid ">>> fib\n"
"<function fib at 10042ed0>\n"
">>> f = fib\n"
">>> f(100)\n"
"0 1 1 2 3 5 8 13 21 34 55 89"
msgstr ""
#: tutorial/controlflow.rst:523
msgid "Coming from other languages, you might object that ``fib`` is not a function but a procedure since it doesn't return a value. In fact, even functions without a :keyword:`return` statement do return a value, albeit a rather boring one. This value is called ``None`` (it's a built-in name). Writing the value ``None`` is normally suppressed by the interpreter if it would be the only value written. You can see it if you really want to using :func:`print`::"
msgstr ""
#: tutorial/controlflow.rst:530
msgid ">>> fib(0)\n"
">>> print(fib(0))\n"
"None"
msgstr ""
#: tutorial/controlflow.rst:534
msgid "It is simple to write a function that returns a list of the numbers of the Fibonacci series, instead of printing it::"
msgstr ""
#: tutorial/controlflow.rst:537
msgid ">>> def fib2(n): # return Fibonacci series up to n\n"
"... \"\"\"Return a list containing the Fibonacci series up to n.\"\"\"\n"
"... result = []\n"
"... a, b = 0, 1\n"
"... while a < n:\n"
"... result.append(a) # see below\n"
"... a, b = b, a+b\n"
"... return result\n"
"...\n"
">>> f100 = fib2(100) # call it\n"
">>> f100 # write the result\n"
"[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]"
msgstr ""
#: tutorial/controlflow.rst:550
msgid "This example, as usual, demonstrates some new Python features:"
msgstr ""
#: tutorial/controlflow.rst:552
msgid "The :keyword:`return` statement returns with a value from a function. :keyword:`!return` without an expression argument returns ``None``. Falling off the end of a function also returns ``None``."
msgstr ""
#: tutorial/controlflow.rst:556
msgid "The statement ``result.append(a)`` calls a *method* of the list object ``result``. A method is a function that 'belongs' to an object and is named ``obj.methodname``, where ``obj`` is some object (this may be an expression), and ``methodname`` is the name of a method that is defined by the object's type. Different types define different methods. Methods of different types may have the same name without causing ambiguity. (It is possible to define your own object types and methods, using *classes*, see :ref:`tut-classes`) The method :meth:`!append` shown in the example is defined for list objects; it adds a new element at the end of the list. In this example it is equivalent to ``result = result + [a]``, but more efficient."
msgstr ""
#: tutorial/controlflow.rst:571
msgid "More on Defining Functions"
msgstr ""
#: tutorial/controlflow.rst:573
msgid "It is also possible to define functions with a variable number of arguments. There are three forms, which can be combined."
msgstr ""
#: tutorial/controlflow.rst:580
msgid "Default Argument Values"
msgstr ""
#: tutorial/controlflow.rst:582
msgid "The most useful form is to specify a default value for one or more arguments. This creates a function that can be called with fewer arguments than it is defined to allow. For example::"
msgstr ""
#: tutorial/controlflow.rst:586
msgid "def ask_ok(prompt, retries=4, reminder='Please try again!'):\n"
" while True:\n"
" reply = input(prompt)\n"
" if reply in {'y', 'ye', 'yes'}:\n"
" return True\n"
" if reply in {'n', 'no', 'nop', 'nope'}:\n"
" return False\n"
" retries = retries - 1\n"
" if retries < 0:\n"
" raise ValueError('invalid user response')\n"
" print(reminder)"
msgstr ""
#: tutorial/controlflow.rst:598
msgid "This function can be called in several ways:"
msgstr ""
#: tutorial/controlflow.rst:600
msgid "giving only the mandatory argument: ``ask_ok('Do you really want to quit?')``"
msgstr ""
#: tutorial/controlflow.rst:602
msgid "giving one of the optional arguments: ``ask_ok('OK to overwrite the file?', 2)``"
msgstr ""
#: tutorial/controlflow.rst:604
msgid "or even giving all arguments: ``ask_ok('OK to overwrite the file?', 2, 'Come on, only yes or no!')``"
msgstr ""
#: tutorial/controlflow.rst:607
msgid "This example also introduces the :keyword:`in` keyword. This tests whether or not a sequence contains a certain value."
msgstr ""
#: tutorial/controlflow.rst:610
msgid "The default values are evaluated at the point of function definition in the *defining* scope, so that ::"
msgstr ""
#: tutorial/controlflow.rst:613
msgid "i = 5\n"
"\n"
"def f(arg=i):\n"
" print(arg)\n"
"\n"
"i = 6\n"
"f()"
msgstr ""
#: tutorial/controlflow.rst:621
msgid "will print ``5``."
msgstr ""
#: tutorial/controlflow.rst:623
msgid "**Important warning:** The default value is evaluated only once. This makes a difference when the default is a mutable object such as a list, dictionary, or instances of most classes. For example, the following function accumulates the arguments passed to it on subsequent calls::"
msgstr ""
#: tutorial/controlflow.rst:628
msgid "def f(a, L=[]):\n"
" L.append(a)\n"
" return L\n"
"\n"
"print(f(1))\n"
"print(f(2))\n"
"print(f(3))"
msgstr ""
#: tutorial/controlflow.rst:636
msgid "This will print ::"
msgstr ""
#: tutorial/controlflow.rst:638
msgid "[1]\n"
"[1, 2]\n"
"[1, 2, 3]"
msgstr ""
#: tutorial/controlflow.rst:642
msgid "If you don't want the default to be shared between subsequent calls, you can write the function like this instead::"
msgstr ""
#: tutorial/controlflow.rst:645
msgid "def f(a, L=None):\n"
" if L is None:\n"
" L = []\n"
" L.append(a)\n"
" return L"
msgstr ""
#: tutorial/controlflow.rst:655
msgid "Keyword Arguments"
msgstr ""
#: tutorial/controlflow.rst:657
msgid "Functions can also be called using :term:`keyword arguments <keyword argument>` of the form ``kwarg=value``. For instance, the following function::"
msgstr ""
#: tutorial/controlflow.rst:660
msgid "def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):\n"
" print(\"-- This parrot wouldn't\", action, end=' ')\n"
" print(\"if you put\", voltage, \"volts through it.\")\n"
" print(\"-- Lovely plumage, the\", type)\n"
" print(\"-- It's\", state, \"!\")"
msgstr ""
#: tutorial/controlflow.rst:666
msgid "accepts one required argument (``voltage``) and three optional arguments (``state``, ``action``, and ``type``). This function can be called in any of the following ways::"
msgstr ""
#: tutorial/controlflow.rst:670
msgid "parrot(1000) # 1 positional argument\n"
"parrot(voltage=1000) # 1 keyword argument\n"
"parrot(voltage=1000000, action='VOOOOOM') # 2 keyword arguments\n"
"parrot(action='VOOOOOM', voltage=1000000) # 2 keyword arguments\n"
"parrot('a million', 'bereft of life', 'jump') # 3 positional arguments\n"
"parrot('a thousand', state='pushing up the daisies') # 1 positional, 1 keyword"
msgstr ""
#: tutorial/controlflow.rst:677
msgid "but all the following calls would be invalid::"
msgstr ""
#: tutorial/controlflow.rst:679
msgid "parrot() # required argument missing\n"
"parrot(voltage=5.0, 'dead') # non-keyword argument after a keyword argument\n"
"parrot(110, voltage=220) # duplicate value for the same argument\n"
"parrot(actor='John Cleese') # unknown keyword argument"
msgstr ""
#: tutorial/controlflow.rst:684
msgid "In a function call, keyword arguments must follow positional arguments. All the keyword arguments passed must match one of the arguments accepted by the function (e.g. ``actor`` is not a valid argument for the ``parrot`` function), and their order is not important. This also includes non-optional arguments (e.g. ``parrot(voltage=1000)`` is valid too). No argument may receive a value more than once. Here's an example that fails due to this restriction::"
msgstr ""
#: tutorial/controlflow.rst:692
msgid ">>> def function(a):\n"
"... pass\n"
"...\n"
">>> function(0, a=0)\n"
"Traceback (most recent call last):\n"
" File \"<stdin>\", line 1, in <module>\n"
"TypeError: function() got multiple values for argument 'a'"
msgstr ""
#: tutorial/controlflow.rst:700
msgid "When a final formal parameter of the form ``**name`` is present, it receives a dictionary (see :ref:`typesmapping`) containing all keyword arguments except for those corresponding to a formal parameter. This may be combined with a formal parameter of the form ``*name`` (described in the next subsection) which receives a :ref:`tuple <tut-tuples>` containing the positional arguments beyond the formal parameter list. (``*name`` must occur before ``**name``.) For example, if we define a function like this::"
msgstr ""
#: tutorial/controlflow.rst:708
msgid "def cheeseshop(kind, *arguments, **keywords):\n"
" print(\"-- Do you have any\", kind, \"?\")\n"
" print(\"-- I'm sorry, we're all out of\", kind)\n"
" for arg in arguments:\n"
" print(arg)\n"
" print(\"-\" * 40)\n"
" for kw in keywords:\n"
" print(kw, \":\", keywords[kw])"
msgstr ""
#: tutorial/controlflow.rst:717
msgid "It could be called like this::"
msgstr ""
#: tutorial/controlflow.rst:719
msgid "cheeseshop(\"Limburger\", \"It's very runny, sir.\",\n"
" \"It's really very, VERY runny, sir.\",\n"
" shopkeeper=\"Michael Palin\",\n"
" client=\"John Cleese\",\n"
" sketch=\"Cheese Shop Sketch\")"
msgstr ""
#: tutorial/controlflow.rst:725
msgid "and of course it would print:"
msgstr ""
#: tutorial/controlflow.rst:727
msgid "-- Do you have any Limburger ?\n"
"-- I'm sorry, we're all out of Limburger\n"
"It's very runny, sir.\n"
"It's really very, VERY runny, sir.\n"
"----------------------------------------\n"
"shopkeeper : Michael Palin\n"
"client : John Cleese\n"
"sketch : Cheese Shop Sketch"
msgstr ""
#: tutorial/controlflow.rst:738
msgid "Note that the order in which the keyword arguments are printed is guaranteed to match the order in which they were provided in the function call."
msgstr ""
#: tutorial/controlflow.rst:742
msgid "Special parameters"
msgstr ""
#: tutorial/controlflow.rst:744
msgid "By default, arguments may be passed to a Python function either by position or explicitly by keyword. For readability and performance, it makes sense to restrict the way arguments can be passed so that a developer need only look at the function definition to determine if items are passed by position, by position or keyword, or by keyword."
msgstr ""
#: tutorial/controlflow.rst:750
msgid "A function definition may look like:"
msgstr ""
#: tutorial/controlflow.rst:752
msgid "def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):\n"
" ----------- ---------- ----------\n"
" | | |\n"
" | Positional or keyword |\n"
" | - Keyword only\n"
" -- Positional only"
msgstr ""
#: tutorial/controlflow.rst:761
msgid "where ``/`` and ``*`` are optional. If used, these symbols indicate the kind of parameter by how the arguments may be passed to the function: positional-only, positional-or-keyword, and keyword-only. Keyword parameters are also referred to as named parameters."
msgstr ""
#: tutorial/controlflow.rst:768
msgid "Positional-or-Keyword Arguments"
msgstr ""
#: tutorial/controlflow.rst:770
msgid "If ``/`` and ``*`` are not present in the function definition, arguments may be passed to a function by position or by keyword."
msgstr ""
#: tutorial/controlflow.rst:775
msgid "Positional-Only Parameters"
msgstr ""
#: tutorial/controlflow.rst:777
msgid "Looking at this in a bit more detail, it is possible to mark certain parameters as *positional-only*. If *positional-only*, the parameters' order matters, and the parameters cannot be passed by keyword. Positional-only parameters are placed before a ``/`` (forward-slash). The ``/`` is used to logically separate the positional-only parameters from the rest of the parameters. If there is no ``/`` in the function definition, there are no positional-only parameters."
msgstr ""
#: tutorial/controlflow.rst:785
msgid "Parameters following the ``/`` may be *positional-or-keyword* or *keyword-only*."
msgstr ""
#: tutorial/controlflow.rst:789
msgid "Keyword-Only Arguments"
msgstr ""
#: tutorial/controlflow.rst:791
msgid "To mark parameters as *keyword-only*, indicating the parameters must be passed by keyword argument, place an ``*`` in the arguments list just before the first *keyword-only* parameter."
msgstr ""
#: tutorial/controlflow.rst:797
msgid "Function Examples"
msgstr ""
#: tutorial/controlflow.rst:799
msgid "Consider the following example function definitions paying close attention to the markers ``/`` and ``*``::"
msgstr ""
#: tutorial/controlflow.rst:802
msgid ">>> def standard_arg(arg):\n"
"... print(arg)\n"
"...\n"
">>> def pos_only_arg(arg, /):\n"
"... print(arg)\n"
"...\n"
">>> def kwd_only_arg(*, arg):\n"
"... print(arg)\n"
"...\n"
">>> def combined_example(pos_only, /, standard, *, kwd_only):\n"
"... print(pos_only, standard, kwd_only)"
msgstr ""
#: tutorial/controlflow.rst:815
msgid "The first function definition, ``standard_arg``, the most familiar form, places no restrictions on the calling convention and arguments may be passed by position or keyword::"
msgstr ""
#: tutorial/controlflow.rst:819
msgid ">>> standard_arg(2)\n"
"2\n"
"\n"
">>> standard_arg(arg=2)\n"
"2"
msgstr ""
#: tutorial/controlflow.rst:825
msgid "The second function ``pos_only_arg`` is restricted to only use positional parameters as there is a ``/`` in the function definition::"
msgstr ""
#: tutorial/controlflow.rst:828
msgid ">>> pos_only_arg(1)\n"
"1\n"
"\n"
">>> pos_only_arg(arg=1)\n"
"Traceback (most recent call last):\n"
" File \"<stdin>\", line 1, in <module>\n"
"TypeError: pos_only_arg() got some positional-only arguments passed as keyword arguments: 'arg'"
msgstr ""
#: tutorial/controlflow.rst:836
msgid "The third function ``kwd_only_arg`` only allows keyword arguments as indicated by a ``*`` in the function definition::"
msgstr ""
#: tutorial/controlflow.rst:839
msgid ">>> kwd_only_arg(3)\n"
"Traceback (most recent call last):\n"
" File \"<stdin>\", line 1, in <module>\n"
"TypeError: kwd_only_arg() takes 0 positional arguments but 1 was given\n"
"\n"
">>> kwd_only_arg(arg=3)\n"
"3"
msgstr ""
#: tutorial/controlflow.rst:847
msgid "And the last uses all three calling conventions in the same function definition::"
msgstr ""
#: tutorial/controlflow.rst:850
msgid ">>> combined_example(1, 2, 3)\n"
"Traceback (most recent call last):\n"
" File \"<stdin>\", line 1, in <module>\n"
"TypeError: combined_example() takes 2 positional arguments but 3 were given\n"
"\n"
">>> combined_example(1, 2, kwd_only=3)\n"
"1 2 3\n"
"\n"
">>> combined_example(1, standard=2, kwd_only=3)\n"
"1 2 3\n"
"\n"
">>> combined_example(pos_only=1, standard=2, kwd_only=3)\n"
"Traceback (most recent call last):\n"
" File \"<stdin>\", line 1, in <module>\n"
"TypeError: combined_example() got some positional-only arguments passed as keyword arguments: 'pos_only'"
msgstr ""
#: tutorial/controlflow.rst:867
msgid "Finally, consider this function definition which has a potential collision between the positional argument ``name`` and ``**kwds`` which has ``name`` as a key::"
msgstr ""
#: tutorial/controlflow.rst:869
msgid "def foo(name, **kwds):\n"
" return 'name' in kwds"
msgstr ""
#: tutorial/controlflow.rst:872
msgid "There is no possible call that will make it return ``True`` as the keyword ``'name'`` will always bind to the first parameter. For example::"
msgstr ""
#: tutorial/controlflow.rst:875
msgid ">>> foo(1, **{'name': 2})\n"
"Traceback (most recent call last):\n"
" File \"<stdin>\", line 1, in <module>\n"
"TypeError: foo() got multiple values for argument 'name'\n"
">>>"
msgstr ""
#: tutorial/controlflow.rst:881
msgid "But using ``/`` (positional only arguments), it is possible since it allows ``name`` as a positional argument and ``'name'`` as a key in the keyword arguments::"
msgstr ""
#: tutorial/controlflow.rst:883
msgid ">>> def foo(name, /, **kwds):\n"
"... return 'name' in kwds\n"
"...\n"
">>> foo(1, **{'name': 2})\n"
"True"
msgstr ""
#: tutorial/controlflow.rst:889
msgid "In other words, the names of positional-only parameters can be used in ``**kwds`` without ambiguity."
msgstr ""
#: tutorial/controlflow.rst:894
msgid "Recap"
msgstr ""
#: tutorial/controlflow.rst:896
msgid "The use case will determine which parameters to use in the function definition::"
msgstr ""
#: tutorial/controlflow.rst:898
msgid "def f(pos1, pos2, /, pos_or_kwd, *, kwd1, kwd2):"
msgstr ""
#: tutorial/controlflow.rst:900
msgid "As guidance:"
msgstr ""
#: tutorial/controlflow.rst:902
msgid "Use positional-only if you want the name of the parameters to not be available to the user. This is useful when parameter names have no real meaning, if you want to enforce the order of the arguments when the function is called or if you need to take some positional parameters and arbitrary keywords."
msgstr ""
#: tutorial/controlflow.rst:907
msgid "Use keyword-only when names have meaning and the function definition is more understandable by being explicit with names or you want to prevent users relying on the position of the argument being passed."
msgstr ""
#: tutorial/controlflow.rst:910
msgid "For an API, use positional-only to prevent breaking API changes if the parameter's name is modified in the future."
msgstr ""