flake8-comprehensions
A flake8 plugin that helps you write better list/set/dict comprehensions.
Requirements
Python 3.7 to 3.10 supported.
Installation
First, install with pip
:
python -m pip install flake8-comprehensions
Second, if you define Flake8’s select
setting, add the C4
prefix to it.
Otherwise, the plugin should be active by default.
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Rules
<list/set/dict>
comprehension.
C400-402: Unnecessary generator - rewrite as a It's unnecessary to use list
, set
, or dict
around a generator expression, since there are equivalent comprehensions for these types.
For example:
- Rewrite
list(f(x) for x in foo)
as[f(x) for x in foo]
- Rewrite
set(f(x) for x in foo)
as{f(x) for x in foo}
- Rewrite
dict((x, f(x)) for x in foo)
as{x: f(x) for x in foo}
<set/dict>
comprehension.
C403-404: Unnecessary list comprehension - rewrite as a 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:
- Rewrite
set([f(x) for x in foo])
as{f(x) for x in foo}
- Rewrite
dict([(x, f(x)) for x in foo])
as{x: f(x) for x in foo}
<list/tuple>
literal - rewrite as a <set/dict>
literal.
C405-406: Unnecessary It's unnecessary to use a list or tuple literal within a call to set
or dict
.
For example:
- Rewrite
set([1, 2])
as{1, 2}
- Rewrite
set((1, 2))
as{1, 2}
- Rewrite
set([])
asset()
- Rewrite
dict([(1, 2)])
as{1: 2}
- Rewrite
dict(((1, 2),))
as{1: 2}
- Rewrite
dict([])
as{}
<dict/list/tuple>
call - rewrite as a literal.
C408: Unnecessary 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:
- Rewrite
dict()
as{}
- Rewrite
dict(a=1, b=2)
as{"a": 1, "b": 2}
- Rewrite
list()
as[]
- Rewrite
tuple()
as()
<list/tuple>
passed to <list/tuple>
() - (remove the outer call to <list/tuple>``()/rewrite as a ``<list/tuple>
literal).
C409-410: Unnecessary It's unnecessary to use a list or tuple literal within a call to list
or tuple
, since there is literal syntax for these types.
For example:
- Rewrite
tuple([1, 2])
as(1, 2)
- Rewrite
tuple((1, 2))
as(1, 2)
- Rewrite
tuple([])
as()
- Rewrite
list([1, 2])
as[1, 2]
- Rewrite
list((1, 2))
as[1, 2]
- Rewrite
list([])
as[]
C411: Unnecessary list call - remove the outer call to list().
It's unnecessary to use a list
around a list comprehension, since it is equivalent without it.
For example:
- Rewrite
list([f(x) for x in foo])
as[f(x) for x in foo]
<list/reversed>
call around sorted().
C413: Unnecessary It's unnecessary to use list()
around sorted()
as it already returns a list.
It is also unnecessary to use reversed()
around sorted()
as the latter has a reverse
argument.
For example:
- Rewrite
list(sorted([2, 3, 1]))
assorted([2, 3, 1])
- Rewrite
reversed(sorted([2, 3, 1]))
assorted([2, 3, 1], reverse=True)
- Rewrite
reversed(sorted([2, 3, 1], reverse=True))
assorted([2, 3, 1])
<list/reversed/set/sorted/tuple>
call within <list/set/sorted/tuple>
().
C414: Unnecessary It's unnecessary to double-cast or double-process iterables by wrapping the listed functions within list
/set
/sorted
/tuple
.
For example:
- Rewrite
list(list(iterable))
aslist(iterable)
- Rewrite
list(tuple(iterable))
aslist(iterable)
- Rewrite
tuple(list(iterable))
astuple(iterable)
- Rewrite
tuple(tuple(iterable))
astuple(iterable)
- Rewrite
set(set(iterable))
asset(iterable)
- Rewrite
set(list(iterable))
asset(iterable)
- Rewrite
set(tuple(iterable))
asset(iterable)
- Rewrite
set(sorted(iterable))
asset(iterable)
- Rewrite
set(reversed(iterable))
asset(iterable)
- Rewrite
sorted(list(iterable))
assorted(iterable)
- Rewrite
sorted(tuple(iterable))
assorted(iterable)
- Rewrite
sorted(sorted(iterable))
assorted(iterable)
- Rewrite
sorted(reversed(iterable))
assorted(iterable)
<reversed/set/sorted>
().
C415: Unnecessary subscript reversal of iterable within It's unnecessary to reverse the order of an iterable when passing it into one of the listed functions will change the order again. For example:
- Rewrite
set(iterable[::-1])
asset(iterable)
- Rewrite
sorted(iterable)[::-1]
assorted(iterable, reverse=True)
- Rewrite
reversed(iterable[::-1])
asiterable
<list/set>
comprehension - rewrite using <list/set>
().
C416: Unnecessary It's unnecessary to use a list comprehension if the elements are unchanged.
The iterable should be wrapped in list()
or set()
instead.
For example:
- Rewrite
[x for x in iterable]
aslist(iterable)
- Rewrite
{x for x in iterable}
asset(iterable)