Question

I want to do this:

d = {1: 2, 3: 4}
if 4 in d:
    print('Aha!')

but I want to read from the values and not the keys. What’s the Pythonic way to do this?

Answer 1

Use values¹:

d = {1: 2, 3: 4}
if 4 in d.values():
    print('Aha!')

Note that this will be much slower than a key lookup because it will potentially require inspecting all values in the dictionary. If you need to perform this operation often you might want to consider storing the values in a set.

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¹itervalues in Python 2