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المقال الأصلي : PEP-0008

الرخصة : ملكية عامة مشاع - Public domain

مقدمة

هذه الوثيقة بمثابة قواعد لتنسيق الكود في مكتبة الإصدار الرسميّ لبايثون.

هذه الوثيقة مبنيّة على Guido's original Python Style Guide essay 2 و بعض الإضافات من Barry's style guide 5 و عند التعارض أعتُمد على وثيقة جيدو و الوثيقة ما زالت غير مكتملة و لربما لن تكتمل أبدا .

الاتساق الأعمى

من أراء جيدو الأساسية “الكود يُقرأ أكثر مما يُكتب بكثير” لذا فالإرشادات المقدمة هنا تهدف إلى تحسين قابلية قراءة الكود و اتساقه مع الوسط المحيط من كود بايثون كما يقال فى pep-0020 الفقرة 6 “يُعتد بقابلية القراءة” .

دليل التنسيق أساسه الاتساق فالتوافق مع دليل التنسيق مهم جدا و لكن الاتساق داخل المشروع أكثر أهمية و الاتساق مع وحدة أو دالة ما هو الأكثر أهمية على الإطلاق .

من المهم جدا أن تعرف كيف تتوافق مع الأشياء – ففي بعض الأحيان دليل التنسيق لن ينطبق و هنا عليك أن تستخدم قدراتك بالإضافة للإطلاع على الأمثلة لتقرّر ما هو الأفضل ولا تترد أبدا في السؤال!.

سببين جيدين لكسر قاعدة معينة:

إذا كان تطبيق القواعد سيجعل الكود أقل قابلية للقراءة حتى بالنسبة لشخص تعوّد على قراءة الأكواد المتبعة للقواعد.

عدم كسر التوافقية مع باقي الكود الذي يكسر القواعد أيضا- ربما لأسباب تاريخية - بالرغم من أنها فرصة لتنظيف الكود ككل.

النسق

الإزاحة (indentation)

استخدم 4 مسافات لكل مستوى إزاحة.

المسافات أم الألسنة ؟؟

لا تقم أبدا بالخلط في استخدام المسافات والألسنة .

الوسيلة الأكثر شعبية في بايثون للإزاحات هي استخدام المسافات فقط والطريقة الثانية في ترتيب شعبية الاستعمال هي استخدام الألسنة وحدها لهذا يجب تعديل الكود الذي تستخدم فيه إزاحات مختلطة من المسافات والألسنة ليصبح مسافات فقط .

عند استدعاء مفسر البايثون من سطر الأوامر مع الخاصية t- سيخرج لك تحذيرات بخصوص استخدام خليط من المسافات والألسنة، أما عند استخدام tt- فهذه التحذيرات ستعتبر أخطاء. لذ يوصى بشدة باستعمال هذه الخواص .

الطول الأقصى للسطر

حدد الطول الأقصى لكل سطر ب 79 حرف .

لا يزال إلى الآن توجد العديد من الأجهزة المحدودة ب 80 حرف للسطر بالإضافة إلى أن تحديد النافذة ب 80 يجعل بالإمكان الحصول على عدة نوافذ متجانبة (warping)الافتراضي على هذه الأجهزة يفسد هيكلية عرض الكود و يصعّب قراءته وفهمه .لذا فضلا حدّد الطول الأقصى لكل سطر ب 79 حرفا. أما بالنسبة للوحدات الطويلة من النصوص مثل docstrings أو التعليقات يفضل تحديد الطول الأقصى ب 72 حرفا .

الطريقة المثلى في طي سطور النصوص الطويلة هي استخدام الخط المائل \ و الأقواس . تأكد من إزاحة السطر الجديد بشكل مناسب. الوسيلة المثلى للطي حول العوامل - مثل == ,=< - هي الطي بعدها مباشرة وليس قبلها .

أمثلة على الطي :

    class Rectangle(Blob):
 
        def __init__(self, width, height,
                     color='black', emphasis=None, highlight=0):
            if width == 0 and height == 0 and \
               color == 'red' and emphasis == 'strong' or \
               highlight > 100:
                raise ValueError("sorry, you lose")
            if width == 0 and height == 0 and (color == 'red' or
                                               emphasis is None):
                raise ValueError("I don't think so -- values are %s, %s" %
                                 (width, height))
            Blob.__init__(self, width, height,
                          color, emphasis, highlight)

الأسطر الفارغة

افصل بين الدوال الرئيسة والكلاسات بسطرين فارغين

تعريف ال method داخل كلاس تفصل بسطر فارغ واحد .

يمكن استخدام الأسطر الفارغة (برُشد) لفصل مجموعات من الدوال مترابطة المضمون .

استعمل الأسطر الفارغة داخل الدوال (برُشد) لتحديد الأقسام المنطقية .

تتعامل بايثون مع control-L (^L) كمسافة .بينما تعاملها مع العديد من الأدوات كفواصل للصفحات. لذا بإمكانك استخدامها لتنظيم الكود إلى أقسام وصفحات .

الترميز

Code in the core Python distribution should aways use the ASCII or Latin-1 encoding (a.k.a. ISO-8859-1). For Python 3.0 and beyond, UTF-8 is preferred over Latin-1, see PEP 3120.

Files using ASCII (or UTF-8, for Python 3.0) should not have a coding cookie. Latin-1 (or UTF-8) should only be used when a comment or docstring needs to mention an author name that requires Latin-1; otherwise, using \x, \u or \U escapes is the preferred way to include non-ASCII data in string literals.

For Python 3.0 and beyond, the following policy is prescribed for the standard library (see PEP 3131): All identifiers in the Python standard library MUST use ASCII-only identifiers, and SHOULD use English words wherever feasible (in many cases, abbreviations and technical terms are used which aren't English). In addition, string literals and comments must also be in ASCII. The only exceptions are (a) test cases testing the non-ASCII features, and (b) names of authors. Authors whose names are not based on the latin alphabet MUST provide a latin transliteration of their names.

Open source projects with a global audience are encouraged to adopt a similar policy.

الاستيراد

- Imports should usually be on separate lines, e.g.:

Yes: import os

import sys

No: import sys, os

it's okay to say this though:

from subprocess import Popen, PIPE

- Imports are always put at the top of the file, just after any module comments and docstrings, and before module globals and constants.

Imports should be grouped in the following order:

    1. standard library imports
    2. related third party imports
    3. local application/library specific imports

You should put a blank line between each group of imports.

Put any relevant all specification after the imports.

- Relative imports for intra-package imports are highly discouraged. Always use the absolute package path for all imports. Even now that PEP 328 [7] is fully implemented in Python 2.5, its style of explicit relative imports is actively discouraged; absolute imports are more portable and usually more readable.

- When importing a class from a class-containing module, it's usually okay to spell this

from myclass import MyClass from foo.bar.yourclass import YourClass

If this spelling causes local name clashes, then spell them

      import myclass
      import foo.bar.yourclass

and use “myclass.MyClass” and “foo.bar.yourclass.YourClass”

المسافات البيضاء فى التعابير و الجمل البرمجية

Pet Peeves

Avoid extraneous whitespace in the following situations:

- Immediately inside parentheses, brackets or braces.

    Yes: spam(ham[1], {eggs: 2})
    No:  spam( ham[ 1 ], { eggs: 2 } )

Immediately before a comma, semicolon, or colon:

    Yes: if x == 4: print x, y; x, y = y, x
    No:  if x == 4 : print x , y ; x , y = y , x

- Immediately before the open parenthesis that starts the argument

    list of a function call:

    Yes: spam(1)
    No:  spam (1)

- Immediately before the open parenthesis that starts an indexing or

    slicing:

    Yes: dict['key'] = list[index]
    No:  dict ['key'] = list [index]

- More than one space around an assignment (or other) operator to

    align it with another.

    Yes:

        x = 1
        y = 2
        long_variable = 3

No:

        x             = 1
        y             = 2
        long_variable = 3

توصيات أخرى

- Always surround these binary operators with a single space on either side: assignment (, augmented assignment (+=, -= etc.), comparisons (==, <, >, !=, <>, ⇐, >=, in, not in, is, is not), Booleans (and, or, not).

- Use spaces around arithmetic operators:

Yes:

        i = i + 1
        submitted += 1
        x = x * 2 - 1
        hypot2 = x * x + y * y
        c = (a + b) * (a - b)

No:

        i=i+1
        submitted +=1
        x = x*2 - 1
        hypot2 = x*x + y*y
        c = (a+b) * (a-b)

- Don't use spaces around the '=' sign when used to indicate a keyword argument or a default parameter value.

    Yes:

        def complex(real, imag=0.0):
            return magic(r=real, i=imag)

No:

        def complex(real, imag = 0.0):
            return magic(r = real, i = imag)

- Compound statements (multiple statements on the same line) are generally discouraged.

    Yes:

        if foo == 'blah':
            do_blah_thing()
        do_one()
        do_two()
        do_three()

Rather not:

        if foo == 'blah': do_blah_thing()
        do_one(); do_two(); do_three()

While sometimes it's okay to put an if/for/while with a small body on the same line, never do this for multi-clause statements. Also avoid folding such long lines!

    Rather not:

        if foo == 'blah': do_blah_thing()
        for x in lst: total += x
        while t < 10: t = delay()

    Definitely not:

        if foo == 'blah': do_blah_thing()
        else: do_non_blah_thing()

        try: something()
        finally: cleanup()

        do_one(); do_two(); do_three(long, argument,
                                     list, like, this)

        if foo == 'blah': one(); two(); three()

نصوص التوثيق Docstrings

Conventions for writing good documentation strings (a.k.a. “docstrings”) are immortalized in PEP 257 [3].

Write docstrings for all public modules, functions, classes, and methods. Docstrings are not necessary for non-public methods, but you should have a comment that describes what the method does. This comment should appear after the “def” line.

PEP 257 describes good docstring conventions. Note that most importantly, the “”“ that ends a multiline docstring should be on a line by itself, and preferably preceded by a blank line, e.g.:

    """Return a foobang

Optional plotz says to frobnicate the bizbaz first.

"""

For one liner docstrings, it's okay to keep the closing ”“” on the same line.

Version Bookkeeping

If you have to have Subversion, CVS, or RCS crud in your source file, do it as follows.

      __version__ = "$Revision: 63990 $"
      # $Source$

These lines should be included after the module's docstring, before any other code, separated by a blank line above and below.

Naming Conventions

The naming conventions of Python's library are a bit of a mess, so we'll never get this completely consistent – nevertheless, here are the currently recommended naming standards. New modules and packages (including third party frameworks) should be written to these standards, but where an existing library has a different style, internal consistency is preferred.

Descriptive: Naming Styles

There are a lot of different naming styles. It helps to be able to recognize what naming style is being used, independently from what they are used for.

The following naming styles are commonly distinguished:

b (single lowercase letter)

B (single uppercase letter)

lowercase

lower_case_with_underscores

UPPERCASE

UPPER_CASE_WITH_UNDERSCORES

CapitalizedWords (or CapWords, or CamelCase – so named because

of the bumpy look of its letters[4]). This is also sometimes known as

    StudlyCaps.

    Note: When using abbreviations in CapWords, capitalize all the letters
    of the abbreviation.  Thus HTTPServerError is better than
    HttpServerError.

mixedCase (differs from CapitalizedWords by initial lowercase

character!)

Capitalized_Words_With_Underscores (ugly!)

There's also the style of using a short unique prefix to group related names together. This is not used much in Python, but it is mentioned for completeness. For example, the os.stat() function returns a tuple whose items traditionally have names like st_mode, st_size, st_mtime and so on. (This is done to emphasize the correspondence with the fields of the POSIX system call struct, which helps programmers familiar with that.)

The X11 library uses a leading X for all its public functions. In Python, this style is generally deemed unnecessary because attribute and method names are prefixed with an object, and function names are prefixed with a module name.

In addition, the following special forms using leading or trailing underscores are recognized (these can generally be combined with any case convention):

_single_leading_underscore: weak “internal use” indicator. E.g. “from M

import *” does not import objects whose name starts with an underscore.

single_trailing_underscore_: used by convention to avoid conflicts with

Python keyword, e.g. Tkinter.Toplevel(master, class_='ClassName')

 __double_leading_underscore: when naming a class attribute,invokes namemangling (inside class FooBar, __boo becomes _FooBar__boo; see below).

double_leading_and_trailing_underscore: “magic” objects or attributes that live in user-controlled namespaces. E.g. init, import or file. Never invent such names; only use them as documented.

Prescriptive: Naming Conventions

  Names to Avoid

    Never use the characters `l' (lowercase letter el), `O' (uppercase
    letter oh), or `I' (uppercase letter eye) as single character variable
    names.

    In some fonts, these characters are indistinguishable from the numerals
    one and zero.  When tempted to use `l', use `L' instead.

  Package and Module Names

    Modules should have short, all-lowercase names.  Underscores can be used
    in the module name if it improves readability.  Python packages should
    also have short, all-lowercase names, although the use of underscores is
    discouraged.

    Since module names are mapped to file names, and some file systems are
    case insensitive and truncate long names, it is important that module
    names be chosen to be fairly short -- this won't be a problem on Unix,
    but it may be a problem when the code is transported to older Mac or
    Windows versions, or DOS.

    When an extension module written in C or C++ has an accompanying Python
    module that provides a higher level (e.g. more object oriented)
    interface, the C/C++ module has a leading underscore (e.g. _socket).

  Class Names

    Almost without exception, class names use the CapWords convention.
    Classes for internal use have a leading underscore in addition.

  Exception Names

    Because exceptions should be classes, the class naming convention
    applies here.  However, you should use the suffix "Error" on your
    exception names (if the exception actually is an error).

  Global Variable Names

    (Let's hope that these variables are meant for use inside one module
    only.)  The conventions are about the same as those for functions.

    Modules that are designed for use via "from M import *" should use the
    __all__ mechanism to prevent exporting globals, or use the older
    convention of prefixing such globals with an underscore (which you might
    want to do to indicate these globals are "module non-public").

  Function Names

    Function names should be lowercase, with words separated by underscores
    as necessary to improve readability.

    mixedCase is allowed only in contexts where that's already the
    prevailing style (e.g. threading.py), to retain backwards compatibility.

  Function and method arguments

    Always use 'self' for the first argument to instance methods.

    Always use 'cls' for the first argument to class methods.

    If a function argument's name clashes with a reserved keyword, it is
    generally better to append a single trailing underscore rather than use
    an abbreviation or spelling corruption.  Thus "print_" is better than
    "prnt".  (Perhaps better is to avoid such clashes by using a synonym.)

  Method Names and Instance Variables

    Use the function naming rules: lowercase with words separated by
    underscores as necessary to improve readability.

    Use one leading underscore only for non-public methods and instance
    variables.

    To avoid name clashes with subclasses, use two leading underscores to
    invoke Python's name mangling rules.

    Python mangles these names with the class name: if class Foo has an
    attribute named __a, it cannot be accessed by Foo.__a.  (An insistent
    user could still gain access by calling Foo._Foo__a.)  Generally, double
    leading underscores should be used only to avoid name conflicts with
    attributes in classes designed to be subclassed.

    Note: there is some controversy about the use of __names (see below).

  Designing for inheritance

    Always decide whether a class's methods and instance variables
    (collectively: "attributes") should be public or non-public.  If in
    doubt, choose non-public; it's easier to make it public later than to
    make a public attribute non-public.

    Public attributes are those that you expect unrelated clients of your
    class to use, with your commitment to avoid backward incompatible
    changes.  Non-public attributes are those that are not intended to be
    used by third parties; you make no guarantees that non-public attributes
    won't change or even be removed.

    We don't use the term "private" here, since no attribute is really
    private in Python (without a generally unnecessary amount of work).

    Another category of attributes are those that are part of the "subclass
    API" (often called "protected" in other languages).  Some classes are
    designed to be inherited from, either to extend or modify aspects of the
    class's behavior.  When designing such a class, take care to make
    explicit decisions about which attributes are public, which are part of
    the subclass API, and which are truly only to be used by your base
    class.

    With this in mind, here are the Pythonic guidelines:

Public attributes should have no leading underscores.

If your public attribute name collides with a reserved keyword, append

a single trailing underscore to your attribute name. This is

      preferable to an abbreviation or corrupted spelling.  (However,
      notwithstanding this rule, 'cls' is the preferred spelling for any
      variable or argument which is known to be a class, especially the
      first argument to a class method.)

      Note 1: See the argument name recommendation above for class methods.

For simple public data attributes, it is best to expose just the

attribute name, without complicated accessor/mutator methods. Keep in

      mind that Python provides an easy path to future enhancement, should
      you find that a simple data attribute needs to grow functional
      behavior.  In that case, use properties to hide functional
      implementation behind simple data attribute access syntax.

      Note 1: Properties only work on new-style classes.

      Note 2: Try to keep the functional behavior side-effect free, although
      side-effects such as caching are generally fine.

      Note 3: Avoid using properties for computationally expensive
      operations; the attribute notation makes the caller believe
      that access is (relatively) cheap.

If your class is intended to be subclassed, and you have attributes

that you do not want subclasses to use, consider naming them with

      double leading underscores and no trailing underscores.  This invokes
      Python's name mangling algorithm, where the name of the class is
      mangled into the attribute name.  This helps avoid attribute name
      collisions should subclasses inadvertently contain attributes with the
      same name.

      Note 1: Note that only the simple class name is used in the mangled
      name, so if a subclass chooses both the same class name and attribute
      name, you can still get name collisions.

      Note 2: Name mangling can make certain uses, such as debugging and
      __getattr__(), less convenient.  However the name mangling algorithm
      is well documented and easy to perform manually.

      Note 3: Not everyone likes name mangling.  Try to balance the
      need to avoid accidental name clashes with potential use by
      advanced callers.

المصادر

PEP 7, Style Guide for C Code, van Rossum
http://www.python.org/doc/essays/styleguide.html
PEP 257, Docstring Conventions, Goodger, van Rossum
http://www.wikipedia.com/wiki/CamelCase
Barry's GNU Mailman style guide
PEP 20, The Zen of Python
PEP 328, Imports: Multi-Line and Absolute/Relative

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