Python - intersect a dict and list

Question

Given the following data structures ,what is the most efficient way to find out the intersection - keys which are common to both the data structures.

dict1 = {'2A':'....','3A':'....','4B':.....}  
list1 = [......,'2A','4B'.....]

Expected output = ['2A','4B']

I am fine to organize the list(not dict1) into any other data-structure if that yields a faster output too. Since this lookup has 2 be done for a large number of dicts - speed is vital.

Answer 1

As suggested by @Blckknght

>>> dict1.viewkeys() & list1
set(['4B', '2A'])

This has to be the fastest and most efficient way. Note that dict.viewkeys() is dict.keys in Python 3 (don't confuse this with Python 2 where dict.keys() returns a list instead)

Answer 2

Use sets.

>>> set(dict1.keys()) & set(list1)