Question

Suppose you have a sequence of 2-tuples:

seq_of_tups = (('a', 1), ('b', 2), ('c', 3))

and you want to test if 'a' is the first item of any tuple in the sequence.

What is the most Pythonic way?

Convert to a dictionary and test for keys, which seems easy enough to understand? i.e.

'a' in dict(seq_of_tups)

Use a cute zip trick which is is not particularly clear unless you know the trick? i.e.

'a' in zip(*seq_of_tups)[0]

Or be really explicit with map? i.e.

'a' in map(lambda tup: tup[0], seq_of_tups)

Or is there a better way than any of these choices?

Answer 1

>>> tups = (('a', 1), ('b', 2), ('c', 3))

>>> 'a' in (x[0] for x in tups)
True
>>> 'd' in (x[0] for x in tups)
False

the above solution will exit as soon as a is found, proof:

>>> tups = (('a', 1),('a',5), ('b', 2), ('c', 3))
>>> gen=(x[0] for x in tups)
>>> 'a' in gen
True
>>> list(gen)
['a', 'b', 'c']  #this result means generator stopped at first 'a'