$ pep8 whitespace.py
 whitespace.py:4:2: E231 missing whitespace after ','

 $ pep8 --show-source whitespace.py
 whitespace.py:4:2: E231 missing whitespace after ','
 a,b = 10, 25
  ^
 $ pep8 --show-pep8 whitespace.py
 whitespace.py:4:2: E231 missing whitespace after ','
     Each comma, semicolon or colon should be followed by whitespace.

     Okay: [a, b]
     Okay: (3,)
     Okay: a[1:4]
     Okay: a[:4]
     Okay: a[1:]
     Okay: a[1:4:2]
     E231: ['a','b']
     E231: foo(bar,baz)
     E231: [{'a':'b'}]