Short Notes on Python PEP8 Style Guide

Aim of this PEP 8 Style Guidelines is to improve readability of code. One of Guido’s key insights is that code is read much more often than it is written.

Code layout

Indentation : 4 spaces are preferred.

Examples :

my_list = [
    1, 2, 3,
    4, 5, 6,
    ]
result = some_function_that_takes_arguments(
    'a', 'b', 'c',
    'd', 'e', 'f',
    )
# Aligned with opening delimiter
foo = long_function_name(var_one, var_two,
                         var_three, var_four)

# More indentation included to distinguish this from the rest.
def long_function_name(
        var_one, var_two, var_three,
        var_four):
    print(var_one)
Tabs or Spaces : Spaces are the preferred indentation method.

Tip: When invoking the Python 2 command line interpreter with the -t option, it issues warnings about code that illegally mixes tabs and spaces. When using -tt these warnings become errors. These options are highly recommended!

Maximum Line Length :

Limit all lines to a maximum of 79 characters

For Docstrings or comments, the line length should be limited to 72 characters.

with open('/path/to/some/file/you/want/to/read') as file_1, \ # Backslash to shorten line

    open('/path/to/some/file/being/written', 'w') as file_2:

    file_2.write(file_1.read())

Make sure to indent the continued line appropriately. The preferred place to break around a binary operator is after the operator, not before it. Some examples:
class Rectangle(Blob):

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)

Blank Lines:

  • For Top level functions, classes : 2 Lines
  • Method def inside class : 1 Line
  • To to indicate logical sections in code : 1 Line

Source File Encoding : UTF-8 (or ASCII in Python 2)

Imports : Imports should usually be on separate lines

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.

Example:

import os
import sys

from subprocess import Popen, PIPE

Comments:

Keep it Simple, Short & Sweet(KISS) and explain  only what it does in simple, in complete sentence. Always make a priority of keeping the comments up-to-date when the code changes!

Comments are costly & use them only when need.

Naming Conventions:

  1. Avoid names with letters I,O,L
  2. Module names should be all-lowercase, short.
  3. Class names should normally use the CapWords convention
  4. Global Variable Names – begin with  underscore(“-“).
  5. Function Names – lower case, underscore
  6. Function and method Args: As Default use, self – for functions and cls – for classes
  7. Constants – All uppercase “MAX_OVERFLOW”
  8. For exceptions handling explicitly define error expected ! Example “except ImportError:” instead of “except:”

Source Link : http://www.python.org/dev/peps/pep-0008/

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