Test if value exists in several lists

问题:

I would like to check if a value exists in every list.

The following returns True as expected, but seems un-pythonic.

What is the correct/more elegant way to do this?

a = [1 ,2] b = [1, 3] c = [1, 4] d = [2, 5]  False in [True if 1 in l else False for l in [a, b, c, d]  ] 

回答1:

You can use all and a generator expression:

all(1 in x for x in (a, b, c, d)) 

Demo:

>>> a = [1 ,2] >>> b = [1, 3] >>> c = [1, 4] >>> d = [2, 5] >>> all(1 in x for x in (a, b, c, d)) False >>> all(1 in x for x in (a, b, c)) True >>> 

In addition to being more readable, this solution is more efficient since it uses lazy-evaluation. It will only check as many items as is necessary to determine the result.

Also, there is never a good reason to do:

True if 1 in l else False 

or something similar since in already returns a boolean result. All you need is:

1 in l 

For the negated version, use:

1 not in l 

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