flake8-comprehensions 3.2.3

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:

• 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}

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:

• 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}

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:

• Rewrite tuple([1, 2]) or tuple((1, 2)) as (1, 2)

• Rewrite tuple([]) as ()

• Rewrite list([1, 2]) or list((1, 2)) as [1, 2]

• Rewrite list([]) as []

• Rewrite set([1, 2]) or set((1, 2)) as {1, 2}

• Rewrite set([]) as set()

• Rewrite dict([(1, 2)]) or dict(((1, 2),)) as {1: 2}

• Rewrite dict([]) 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:

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

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

• Rewrite filter(lambda x: x % 2 == 0, [x ** 3 for x in range(10)]) as filter(lambda x: x % 2 == 0, (x ** 3 for x in range(10)))

The list of builtins that are checked for are:

• all

• any

• enumerate

• filter

• frozenset

• map

• max

• min

• sorted

• sum

• tuple

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

It’s slower to call these types than to construct them with literals, e.g. dict() is slower than {}, because the name dict must be looked up in the global scope in case it has been rebound, and it includes the overhead of a function call. Same for the other two builtin types here. For example:

• Rewrite dict() as {}

• Rewrite list() as []

• Rewrite tuple() 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:

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

C412: Unnecessary (dict/list/set) comprehension - ‘in’ can take a generator.

It’s unnecessary to pass a dict/list/set comprehension to ‘in’ that can take a generator instead. For example:

• Rewrite y in [f(x) for x in foo] as y in (f(x) for x in foo)

• Rewrite y in {x ** 2 for x in foo} as y in (x ** 2 for x in foo)

C413: Unnecessary list/reversed call around sorted().

It’s unnecessary to use list() around sorted() as it already returns a list. It is also suboptimal to use reversed() around sorted() as the latter has a reverse argument. For example:

• Rewrite list(sorted([2, 3, 1])) as sorted([2, 3, 1])

• Rewrite reversed(sorted([2, 3, 1])) as sorted([2, 3, 1], reverse=True)

• Rewrite reversed(sorted([2, 3, 1], reverse=True)) as sorted([2, 3, 1])

C414: Unnecessary (list/reversed/set/sorted/tuple) call within list/set/sorted/tuple().

It’s unnecessary to change the type of the iterable or change the order of elements within certain other function calls that will themselves define the order of the iterable or the type that is output. For example:

• Rewrite list(list(iterable)) as list(iterable)

• Rewrite list(tuple(iterable)) as list(iterable)

• Rewrite tuple(list(iterable)) as tuple(iterable)

• Rewrite tuple(tuple(iterable)) as tuple(iterable)

• Rewrite set(set(iterable)) as set(iterable)

• Rewrite set(list(iterable)) as set(iterable)

• Rewrite set(tuple(iterable)) as set(iterable)

• Rewrite set(sorted(iterable)) as set(iterable)

• Rewrite set(reversed(iterable)) as set(iterable)

• Rewrite sorted(list(iterable)) as sorted(iterable)

• Rewrite sorted(tuple(iterable)) as sorted(iterable)

• Rewrite sorted(sorted(iterable)) as sorted(iterable)

• Rewrite sorted(reversed(iterable)) as sorted(iterable)

C415: Unnecessary subscript reversal of iterable within reversed/set/sorted().

It’s unnecessary to reverse the order of an iterable using a [::-1] before passing it into set() which will randomize the order, sorted() which will return a new sorted list, or reversed() which will effectively return the original iterable. For example:

• Rewrite set(iterable[::-1]) as set(iterable)

• Rewrite sorted(iterable[::-1]) as sorted(iterable, reverse=True)

• Rewrite reversed(iterable[::-1]) as iterable

C416: Unnecessary (list/set) comprehension - rewrite using list/set().

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] as list(iterable)

• Rewrite {x for x in iterable} as set(iterable)