CODEWITHSUNDEEP
python
Fadai Mammadov
Fadai Mammadov

Reputation: 65

When does all() function in Python print False?

x = [0, 1, -2, 3, 4, 5]
all ([i for i in range (1, len(x)) if x [i-1] < x[i]]) ?

Why does this code print True?
1 > -2 so it should print False I think.

Upvotes: 1

Views: 78

Answers (2)

NPE
NPE

Reputation: 500773

Your code doesn't do what you think it does. It first filters out some elements, and then evaluates a bunch of indices for truthiness. Since all of the indices are strictly positive, they are all truthy and your code always evaluates to True.

From your description, what you're actually trying to do is this:

>>> all(x[i-1] < x[i] for i in range (1, len(x)))
False

This iterates over all pairs of consecutive elements and checks whether the first element is less than the second.

Another way to write this is:

>>> all(a < b for (a, b) in zip(x, x[1::]))
False

Upvotes: 5

RemcoGerlich
RemcoGerlich

Reputation: 31270

All values of i come from range(1, len(x)), so they're all positive integers. Positive integers are true-ish, so all() will return True.

Upvotes: 3

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