Question

b = [{'a': 1, 'b': 2}, {'a': 3, 'b': 4}, {'a': 5, 'b': 6}]

How can I determine if b has an entry 'a'=5?

Answer 1

Use any() with a generator expression:

if any(x["a"] == 5 for x in b):
    # whatever

This will stop iterating b as soon as the first match is found.

If you like functional programming, you can also do

from operator import itemgetter
from itertools import imap
if 5 in imap(itemgetter("a"), b):
    # whatever

I’m pretty sure though most people, me included, would prefer the first variant.