PEP 8 -- Style Guide for Python Code (2)

Whitespace in Expressions and Statements
1. Pet Peeves
  a. Avoid extraneous whitespace in the following situations:
    (1) Immediately inside parentheses, brackets or braces.
    Yes: spam(ham[1], {eggs: 2})
    No:  spam( ham[ 1 ], { eggs: 2 } )
    (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

    (3) Immediately before the open parenthesis that starts the argument list of a function call:

    Yes: spam(1)

    No:  spam (1)

    (4) Immediately before the open parenthesis that starts an indexing or slicing:

    Yes: dict['key'] = list[index]

    No:  dict ['key'] = list [index]

    (5) 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

2. Other Recommendations

  a. 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).

  b. 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)

  c. 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)

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

  Yes:

       if foo == 'blah':

           do_blah_thing()

       do_one()

       do_two()

       do_three()

  No:

       if foo == 'blah': do_blah_thing()

       do_one(); do_two(); do_three()

  e. 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()