CODEWITHSUNDEEP
python
2ank3th
2ank3th

Reputation: 3109

Python iterator over string using keyword in

I recently came across some python code I don't understand completely. 

s = "abcdef"
x = "bde"
it = iter(s)
print all(c in it for c in x)

I understand that this code checks if x is a subsequence of s. Can someone explain or point me towards an article that explains what's exactly happening at c in it. What is calling the next method of iterator it?

Upvotes: 0

Views: 62

Answers (1)

Jens
Jens

Reputation: 9140

It’s good to start with reading the documentation for the built-in function all():

Return True if all elements of the iterable are true (or if the iterable is empty).

That means that c in it for c in x is a “generator expression”: it produces values. The values it produces are of the boolean expression c in it (see the in operator) for all characters c in string x.

Here, the in operator is responsible for advancing the iterator. Note, however, that the True result is probably lucky. The iterator it can advance only once and because x = "bde" contains the letters in the same sequence as they appear in s = "abcdef", the whole expression works out to the expected result True. Reverse x = "edb" and the expression is False because the iterator is exhausted.

Upvotes: 1

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