Check Python source code formatting, according to PEP 8:
For usage and a list of options, try this:
$ python pep8.py -h
This program and its regression test suite live here:
Groups of errors and warnings:
E errors
W warnings
100 indentation
200 whitespace
300 blank lines
400 imports
500 line length
600 deprecation
700 statements
900 syntax error
You can add checks to this program by writing plugins. Each plugin is
a simple function that is called for each line of source code, either
physical or logical.
Physical line:
- Raw line of text from the input file.
Logical line:
- Multi-line statements converted to a single line.
- Stripped left and right.
- Contents of strings replaced with 'xxx' of same length.
- Comments removed.
The check function requests physical or logical lines by the name of
the first argument:
def maximum_line_length(physical_line)
def extraneous_whitespace(logical_line)
def blank_lines(logical_line, blank_lines, indent_level, line_number)
The last example above demonstrates how check plugins can request
additional information with extra arguments. All attributes of the
Checker object are available. Some examples:
lines: a list of the raw lines from the input file
tokens: the tokens that contribute to this logical line
line_number: line number in the input file
blank_lines: blank lines before this one
indent_char: first indentation character in this file (' ' or 't')
indent_level: indentation (with tabs expanded to multiples of 8)
previous_indent_level: indentation on previous line
previous_logical: previous logical line
The docstring of each check function shall be the relevant part of
text from PEP 8. It is printed if the user enables --show-pep8.
Several docstrings contain examples directly from the PEP 8 document.
Okay: spam(ham[1], {eggs: 2})
E201: spam( ham[1], {eggs: 2})
These examples are verified automatically when pep8.py is run with the
--doctest option. You can add examples for your own check functions.
The format is simple: "Okay" or error/warning code followed by colon
and space, the rest of the line is example source code. If you put 'r'
before the docstring, you can use n for newline, t for tab and s
for space.
def blank_lines(logical_line, blank_lines, indent_level, line_number, previous_logical, previous_indent_level):
Separate top-level function and class definitions with two blank lines.
Method definitions inside a class are separated by a single blank line.
Extra blank lines may be used (sparingly) to separate groups of related
functions. Blank lines may be omitted between a bunch of related
one-liners (e.g. a set of dummy implementations).
Use blank lines in functions, sparingly, to indicate logical sections.
Okay: def a():n passnnndef b():n pass
Okay: def a():n passnnn# Foon# Barnndef b():n pass
E301: class Foo:n b = 0n def bar():n pass
E302: def a():n passnndef b(n):n pass
E303: def a():n passnnnndef b(n):n pass
E303: def a():nnnn pass
E304: @decoratornndef a():n pass
def comparison_to_singleton(logical_line):
Comparisons to singletons like None should always be done
with "is" or "is not", never the equality operators.
Okay: if arg is not None:
E711: if arg != None:
E712: if arg == True:
Also, beware of writing if x when you really mean if x is not None --
e.g. when testing whether a variable or argument that defaults to None was
set to some other value. The other value might have a type (such as a
container) that could be false in a boolean context!
def comparison_type(logical_line):
Object type comparisons should always use isinstance() instead of
comparing types directly.
Okay: if isinstance(obj, int):
E721: if type(obj) is type(1):
When checking if an object is a string, keep in mind that it might be a
unicode string too! In Python 2.3, str and unicode have a common base
class, basestring, so you can do:
Okay: if isinstance(obj, basestring):
Okay: if type(a1) is type(b1):
def compound_statements(logical_line):
Compound statements (multiple statements on the same line) are
generally discouraged.
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!
Okay: if foo == 'blah':n do_blah_thing()
Okay: do_one()
Okay: do_two()
Okay: do_three()
E701: if foo == 'blah': do_blah_thing()
E701: for x in lst: total += x
E701: while t < 10: t = delay()
E701: if foo == 'blah': do_blah_thing()
E701: else: do_non_blah_thing()
E701: try: something()
E701: finally: cleanup()
E701: if foo == 'blah': one(); two(); three()
E702: do_one(); do_two(); do_three()
def continuation_line_indentation(logical_line, tokens, indent_level, verbose):
Continuation lines should align wrapped elements either vertically using
Python's implicit line joining inside parentheses, brackets and braces, or
using a hanging indent.
When using a hanging indent the following considerations should be applied:
- there should be no arguments on the first line, and
- further indentation should be used to clearly distinguish itself as a
Okay: a = (n)
E123: a = (n )
Okay: a = (n 42)
E121: a = (n 42)
E122: a = (n42)
E123: a = (n 42n )
E124: a = (24,n 42n)
E125: if (a orn b):n pass
E126: a = (n 42)
E127: a = (24,n 42)
E128: a = (24,n 42)
def expand_indent(line):
Return the amount of indentation.
Tabs are expanded to the next multiple of 8.
>>> expand_indent(' ')
4
>>> expand_indent('t')
8
>>> expand_indent(' t')
8
>>> expand_indent(' t')
8
>>> expand_indent(' t')
16
def explicit_line_join(logical_line, tokens):
Avoid explicit line join between brackets.
The preferred way of wrapping long lines is by using Python's implied line
continuation inside parentheses, brackets and braces. Long lines can be
broken over multiple lines by wrapping expressions in parentheses. These
should be used in preference to using a backslash for line continuation.
E502: aaa = [123, \n 123]
E502: aaa = ("bbb " \n "ccc")
Okay: aaa = [123,n 123]
Okay: aaa = ("bbb "n "ccc")
Okay: aaa = "bbb " \n "ccc"
def find_checks(argument_name):
Find all globally visible functions where the first argument name
starts with argument_name.
def ignore_code(code):
Check if options.ignore contains a prefix of the error code.
If options.select contains a prefix of the error code, do not ignore it.
def imports_on_separate_lines(logical_line):
Imports should usually be on separate lines.
Okay: import osnimport sys
E401: import sys, os
Okay: from subprocess import Popen, PIPE
Okay: from myclas import MyClass
Okay: from foo.bar.yourclass import YourClass
Okay: import myclass
Okay: import foo.bar.yourclass
def indentation(logical_line, previous_logical, indent_char, indent_level, previous_indent_level):
Use 4 spaces per indentation level.
For really old code that you don't want to mess up, you can continue to
use 8-space tabs.
Okay: a = 1
Okay: if a == 0:n a = 1
E111: a = 1
Okay: for item in items:n pass
E112: for item in items:npass
Okay: a = 1nb = 2
E113: a = 1n b = 2
def maximum_line_length(physical_line, max_line_length):
Limit all lines to a maximum of 79 characters.
There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to have
several windows side-by-side. The default wrapping on such devices looks
ugly. Therefore, please limit all lines to a maximum of 79 characters.
For flowing long blocks of text (docstrings or comments), limiting the
length to 72 characters is recommended.
Reports error E501.
def missing_newline(physical_line):
JCR: The last line should have a newline.
Reports warning W292.
def missing_whitespace(logical_line):
JCR: 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)
def missing_whitespace_around_operator(logical_line, tokens):
- 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.
Okay: i = i + 1
Okay: submitted += 1
Okay: x = x * 2 - 1
Okay: hypot2 = x * x + y * y
Okay: c = (a + b) * (a - b)
Okay: foo(bar, key='word', *args, **kwargs)
Okay: baz(**kwargs)
Okay: negative = -1
Okay: spam(-1)
Okay: alpha[:-i]
Okay: if not -5 < x < +5:n pass
Okay: lambda *args, **kw: (args, kw)
E225: i=i+1
E225: submitted +=1
E225: x = x*2 - 1
E225: hypot2 = x*x + y*y
E225: c = (a+b) * (a-b)
E225: c = alpha -4
E225: z = x **y
def mute_string(text):
Replace contents with 'xxx' to prevent syntax matching.
>>> mute_string('"abc"')
'"xxx"'
>>> mute_string("'''abc'''")
"'''xxx'''"
>>> mute_string("r'abc'")
"r'xxx'"
def python_3000_backticks(logical_line):
Backticks are removed in Python 3000.
Use repr() instead.
Okay: val = repr(1 + 2)
W604: val = `1 + 2`
def python_3000_has_key(logical_line):
The {}.has_key() method will be removed in the future version of
Python. Use the 'in' operation instead.
Okay: if "alph" in d:n print d["alph"]
W601: assert d.has_key('alph')
def python_3000_not_equal(logical_line):
!= can also be written <>, but this is an obsolete usage kept for
backwards compatibility only. New code should always use !=.
The older syntax is removed in Python 3000.
Okay: if a != 'no':
W603: if a <> 'no':
def python_3000_raise_comma(logical_line):
When raising an exception, use "raise ValueError('message')"
instead of the older form "raise ValueError, 'message'".
The paren-using form is preferred because when the exception arguments
are long or include string formatting, you don't need to use line
continuation characters thanks to the containing parentheses. The older
form will be removed in Python 3000.
Okay: raise DummyError("Message")
W602: raise DummyError, "Message"
def refresh_checks():
No description.
def run_check(fileName, source):
Parse options and run checks on Python source.
def tabs_obsolete(physical_line):
For new projects, spaces-only are strongly recommended over tabs. Most
editors have features that make this easy to do.
Okay: if True:n return
W191: if True:ntreturn
def tabs_or_spaces(physical_line, indent_char):
Never mix tabs and spaces.
The most popular way of indenting Python is with spaces only. The
second-most popular way is with tabs only. Code indented with a mixture
of tabs and spaces should be converted to using spaces exclusively. When
invoking the Python 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!
Okay: if a == 0:n a = 1n b = 1
E101: if a == 0:n a = 1ntb = 1
def trailing_blank_lines(physical_line, lines, line_number):
JCR: Trailing blank lines are superfluous.
Okay: spam(1)
W391: spam(1)n
def trailing_whitespace(physical_line):
JCR: Trailing whitespace is superfluous.
FBM: Except when it occurs as part of a blank line (i.e. the line is
nothing but whitespace). According to Python docs[1] a line with only
whitespace is considered a blank line, and is to be ignored. However,
matching a blank line to its indentation level avoids mistakenly
terminating a multi-line statement (e.g. class declaration) when
pasting code into the standard Python interpreter.
The warning returned varies on whether the line itself is blank, for easier
filtering for those who want to indent their blank lines.
Okay: spam(1)
W291: spam(1)s
W293: class Foo(object):n n bang = 12
def whitespace_around_comma(logical_line):
Avoid extraneous whitespace in the following situations:
- More than one space around an assignment (or other) operator to
Note: these checks are disabled by default
Okay: a = (1, 2)
E241: a = (1, 2)
E242: a = (1,t2)
def whitespace_around_keywords(logical_line):
Avoid extraneous whitespace around keywords.
Okay: True and False
E271: True and False
E272: True and False
E273: True andtFalse
E274: Truetand False
def whitespace_around_named_parameter_equals(logical_line, tokens):
Don't use spaces around the '=' sign when used to indicate a
keyword argument or a default parameter value.
Okay: def complex(real, imag=0.0):
Okay: return magic(r=real, i=imag)
Okay: boolean(a == b)
Okay: boolean(a != b)
Okay: boolean(a <= b)
Okay: boolean(a >= b)
E251: def complex(real, imag = 0.0):
E251: return magic(r = real, i = imag)
def whitespace_around_operator(logical_line):
Avoid extraneous whitespace in the following situations:
- More than one space around an assignment (or other) operator to
Okay: a = 12 + 3
E221: a = 4 + 5
E222: a = 4 + 5
E223: a = 4t+ 5
E224: a = 4 +t5
def whitespace_before_parameters(logical_line, tokens):
Avoid extraneous whitespace in the following situations:
- Immediately before the open parenthesis that starts the argument
- Immediately before the open parenthesis that starts an indexing or
Okay: spam(1)
E211: spam (1)
Okay: dict['key'] = list[index]
E211: dict ['key'] = list[index]
E211: dict['key'] = list [index]