[] and {} vs list() and dict(), which is better?
我知道它们基本上都是一样的东西，但在风格方面，哪个更好（更多Pythonic），用来创建一个空的列表或字典？
In terms of speed, it's no competition for empty lists/dicts:
>>> from timeit import timeit
>>> timeit("[]")
0.040084982867934334
>>> timeit("list()")
0.17704233359267718
>>> timeit("{}")
0.033620194745424214
>>> timeit("dict()")
0.1821558326547077
and for non-empty:
>>> timeit("[1,2,3]")
0.24316302770330367
>>> timeit("list((1,2,3))")
0.44744206316727286
>>> timeit("list(foo)", setup="foo=(1,2,3)")
0.446036018543964
>>> timeit("{'a':1, 'b':2, 'c':3}")
0.20868602015059423
>>> timeit("dict(a=1, b=2, c=3)")
0.47635635255323905
>>> timeit("dict(bar)", setup="bar=[('a', 1), ('b', 2), ('c', 3)]")
0.9028228448029267
Also, using the bracket notation let's you use list and dictionary comprehensions, which may be reason enough.
In my opinion [] and {} are the most pythonic and readable ways to create empty lists/dicts.
Be wary of set() 's though, for example:
this_set = {5}
some_other_set = {}
Can be confusing. The first creates a set with one element, the second creates an empty dict and not a set.
The dict literal might be a tiny bit faster as its bytecode is shorter:
In [1]: import dis
In [2]: a = lambda: {}
In [3]: b = lambda: dict()
In [4]: dis.dis(a)
1 0 BUILD_MAP 0
3 RETURN_VALUE
In [5]: dis.dis(b)
1 0 LOAD_GLOBAL 0 (dict)
3 CALL_FUNCTION 0
6 RETURN_VALUE
Same applies to the list vs []
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