Pythonic way of saying "if all of the elements in list 1 also exist in list 2"

I want to return true from the if statem开发者_如何学编程ent only if all of the elements from list 1 also exist in list 2 (list 2 is a superset of list 1). What is the most pythonic way of writing this?

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You can use set operations:

if set(list1) <= set(list2):
    #...

Note that the comparison itself is fast, but converting the lists to sets might not (depends on the size of the lists).

Converting to a set also removes any duplicate. So if you have duplicate elements and want to ensure that they are also duplicates in the other list, using sets will not work.

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You can use built-in all() function:

if all(x in sLVals for x in fLVals):
    # do something

In case of using sets think you can take a look at difference method as far as i know it is quite faster way:

if set(fLVals).difference(sLVals):
    # there is a difference
else:
    # no difference

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Either set.issuperset or all(x in L2 for x in L1).

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This one came straight out of good folks at MIT:

from operator import and_
reduce(and_, [x in b for x in a])

I tried to find the "readings.pdf" they had posted for the 6.01 class about a year ago...but I can't find it anymore.

Head to my profile and send me an email, and I'll send you the .pdf where I got this example. It's a very good book, but it doesn't seem to be a part of the class anymore.