CODEWITHSUNDEEP
python-3.x
Rook
Rook

Reputation: 139

Why is a list containing an empty string truthy?

I have caught something in my work returning a list containing an empty string. I've created an example for simplicity:

big_ol_trickster = [""]
if big_ol_trickster:
    foo()
else:
    print("You can't trick me!")

And this conditional would be satisfied every time. So I've got a question for the python wizards out there: Why is [] == False and "" == False but [""] == True?

Upvotes: 1

Views: 386

Answers (1)

rdas
rdas

Reputation: 21275

Empty lists are Falsey. [""] is not empty. It contains a single element (which happens to be Falsey as well). The Falsey-ness is not evaluated recursively.

To know why is that, look at the implementation of the __bool__ dunder method for the list class. This the method that is called to evaluate truth-value in python. And, yes, you can override it.

[False, False] -> this is also Truthy, it can be counter-intuitive. That's why when you try to use sequences in if conditions you sometimes get "truth-value of sequences can be ambiguous, use any() or all() instead"

Upvotes: 6

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