"Unnecessary dict call" false positives

The dict function has 3 forms: dict(**kwarg), dict(mapping, **kwarg), and dict(iterable, **kwarg). I’m not sure if it makes sense to apply this rule to every form.

Here’s one example use case:

def foo(data):
    defaults = {'a': 1, 'b': 2}
    return dict(defaults, **data)

This example could be rewritten to use literals, but it would be less succinct and (I assume, but haven’t confirmed) less performant.

[adamchainz]

Fix released in version 1.4.1 https://pypi.python.org/pypi/flake8-comprehensions

[adamchainz]

Looks like it is, for small dicts at least:

In [1]: def foo(data):
   ...:     defaults = {'a': 1, 'b': 2}
   ...:     return dict(defaults, **data)
   ...:

In [2]: %timeit foo({'c': 3})
397 ns ± 8.3 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

In [3]: def foo(data):
   ...:     return {"a": 1, "b": 2, **data}
   ...:

In [4]: %timeit foo({'c': 3})
266 ns ± 4.57 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)