Python Dictionary Comprehension

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Happy的楠姐
Happy的楠姐 2020-11-21 13:10

Is it possible to create a dictionary comprehension in Python (for the keys)?

Without list comprehensions, you can use something like this:

l = []
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  •  北荒
    北荒 (楼主)
    2020-11-21 14:05

    There are dictionary comprehensions in Python 2.7+, but they don't work quite the way you're trying. Like a list comprehension, they create a new dictionary; you can't use them to add keys to an existing dictionary. Also, you have to specify the keys and values, although of course you can specify a dummy value if you like.

    >>> d = {n: n**2 for n in range(5)}
    >>> print d
    {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
    

    If you want to set them all to True:

    >>> d = {n: True for n in range(5)}
    >>> print d
    {0: True, 1: True, 2: True, 3: True, 4: True}
    

    What you seem to be asking for is a way to set multiple keys at once on an existing dictionary. There's no direct shortcut for that. You can either loop like you already showed, or you could use a dictionary comprehension to create a new dict with the new values, and then do oldDict.update(newDict) to merge the new values into the old dict.

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