flake8-comprehensions 2.0.0

A flake8 plugin to help you write better list/set/dict comprehensions.

flake8-comprehensions

A flake8 plugin that helps you write better list/set/dict comprehensions.

Installation

Install from pip with:

pip install flake8-comprehensions

Python 3.4+ supported.

When installed it will automatically be run as part of flake8; you can check it is being picked up with:

$ flake8 --version
2.4.1 (pep8: 1.7.0, pyflakes: 0.8.1, flake8-comprehensions: 1.0.0, mccabe: 0.3.1) CPython 2.7.11 on Darwin

Rules

Code	Rule
C400	Unnecessary generator - rewrite as a list comprehension.
C401	Unnecessary generator - rewrite as a set comprehension.
C402	Unnecessary generator - rewrite as a dict comprehension.
C403	Unnecessary list comprehension - rewrite as a set comprehension.
C404	Unnecessary list comprehension - rewrite as a dict comprehension.
C405	Unnecessary (list/tuple) literal - rewrite as a set literal.
C406	Unnecessary (list/tuple) literal - rewrite as a dict literal.
C407	Unnecessary list comprehension - ‘<builtin>’ can take a generator.
C408	Unnecessary (dict/list/tuple) call - rewrite as a literal.
C409	Unnecessary (list/tuple) passed to tuple() - (remove the outer call to tuple()/rewrite as a tuple literal).
C410	Unnecessary (list/tuple) passed to list() - (remove the outer call to list()/rewrite as a list literal).
C411	Unnecessary list call - remove the outer call to list().

Examples

C400-402: Unnecessary generator

It’s unnecessary to use list, set, or dict around a generator expression, since there are equivalent comprehensions for these types. For example:

• list(f(x) for x in foo) is better as [f(x) for x in foo]

• set(f(x) for x in foo) is better as {f(x) for x in foo}

• dict((x, f(x)) for x in foo) is better as {x: f(x) for x in foo}

C403-404: Unnecessary list comprehension

It’s unnecessary to use a list comprehension inside a call to set or dict, since there are equivalent comprehensions for these types. For example:

• set([f(x) for x in foo]) is better as {f(x) for x in foo}

• dict([(x, f(x)) for x in foo]) is better as {x: f(x) for x in foo}

C405-406,C409-410: Unnecessary list/tuple literal

It’s unnecessary to use a list or tuple literal within a call to tuple, list, set, or dict since there is literal syntax for these types. For example:

• tuple([1, 2]) and tuple((1, 2)) are better as (1, 2)

• tuple([]) is better as ()

• list([1, 2]) and list((1, 2)) are better as [1, 2]

• list([]) is better as []

• set([1, 2]) and set((1, 2)) are better as {1, 2}

• set([]) is better as set()

• dict([(1, 2)]) and dict(((1, 2),)) are better as {1: 2}

• dict([]) is better as {}

C407: Unnecessary list comprehension - ‘<builtin>’ can take a generator

It’s unnecessary to pass a list comprehension to some builtins that can take generators instead. For example:

• sum([x ** 2 for x in range(10)]) is better as sum(x ** 2 for x in range(10))

• all([foo.bar for foo in foos]) is better as all(foo.bar for foo in foos)

The list of builtins that are checked for are:

• all

• any

• frozenset

• max

• min

• sorted

• sum

• tuple

C408: Unnecessary (dict/list/tuple) call - rewrite as a literal.

It’s slower to call e.g. dict() than using the empty literal, because the name dict must be looked up in the global scope in case it has been rebound. Same for the other two basic types here. For example:

• dict() is better as {}

• list() is better as []

• tuple() is better as ()

C411: Unnecessary list call - remove the outer call to list().

It’s unnecessary to use a list around list comprehension, since it is equivalent without it. For example:

• list([f(x) for x in foo]) is better as [f(x) for x in foo]

History

Pending Release

2.0.0 (2019-02-02)

• Drop Python 2 support, only Python 3.4+ is supported now.

1.4.1 (2017-05-17)

• Fix false positives in C408 for calls using *args or **kwargs.

1.4.0 (2017-05-14)

• Plugin now reserves the full C4XX code space rather than just C40X

• C408 rule that complains about using tuple(), list(), or dict() instead of a literal.

• C409 and C410 rules that complain about an unnecessary list or tuple that could be rewritten as a literal.

• C411 rule that complains about using list comprehension inside a list() call.

1.3.0 (2017-05-01)

• Don’t allow installation with Flake8 3.2.0 which doesn’t enable the plugin. This bug was fixed in Flake8 3.2.1.

• Prevent false positives of C402 from generators of expressions that aren’t two-tuples.

• C405 and C406 now also complain about unnecessary tuple literals.

1.2.1 (2016-06-27)

• C407 rule that complains about unnecessary list comprehensions inside builtins that can work on generators.

1.2.0 (2016-07-11)

• Split all rule codes by type. This allows granular selection of the rules in flake8 configuration.

1.1.1 (2016-04-06)

• Fix crash on method calls

1.1.0 (2016-04-06)

• C401 rule that complains about unnecessary list comprehensions inside calls to set() or dict().

• C402 rule that complains about unnecessary list literals inside calls to set() or dict().

1.0.0 (2016-04-05)

• C400 rule that complains about an unnecessary usage of a generator when a list/set/dict comprehension would do.