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Dictionary literal

Sourcery refactoring id: dict-literal

Description:

Replaces dictionaries created with dict() with {}

Before:

x = dict()

After:

x = {}

Explanation:

The most concise and Pythonic way to create a dictionary is to use the {} notation.

This fits in with the way we create dictionaries with items, saving a bit of mental energy that might be taken up with thinking about two different ways of creating dicts.

x = {'first':"thing"}
Doing things this way has the added advantage of being a nice little performance improvement.

Here are the timings before and after the change:

$ python3 -m timeit "x = dict()"
5000000 loops, best of 5: 69.8 nsec per loop

$ python3 -m timeit "x = {}"
20000000 loops, best of 5: 29.4 nsec per loop
Similar reasoning and performance results hold for replacing list() with [].

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