[Python] How can I check that a list has one and only one truthy value?

In python, I have a list that should have one and only one truthy value (that is, bool(value) is True). Is there a clever way to check for this? Right now, I am just iterating across the list and manually checking:

def only1(l)
true_found = False
for v in l:
if v and not true_found:
true_found=True
elif v and true_found:
return False #"Too Many Trues"
return true_found


This seems inelegant and not very pythonic. Is there a cleverer way to do this?

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