Question

I read “Python Cookbook” and see what in a recipe “Finding the Intersection of Two Dictionaries” authors recommend using such one-liner:

filter(another_dict.has_key, some_dict.keys())

But since Python 3 dictionaries don’t have has_key() method how should I modify suggested code? I suppose there could be some internal __ in__() method or something like this.

Any ideas, please?

Answer 1

Python 3 has dictionary key views instead, a much more powerful concept. Your code can be written as

some_dict.keys() & another_dict.keys()

in Python 3.x. This returns the common keys of the two dictionaries as a set.

This is also available in Python 2.7, using the method dict.viewkeys().

As a closer match of the original code, you could also use a list comprehension:

[key for key in some_dict if key in another_dict]

An even closer match of original code would be to use dict.__contains__(), which is the magic method corresponding to the in operator:

filter(another_dict.__contains__, some_dict.keys())

But please, don’t use this code. I recommend going with the first version, which is the only one highlighting the symmetry between some_dict and another_dict.