[Python-Dev] bool conversion wart? (original) (raw)

Larry Hastings larry at hastings.org
Fri Feb 23 03:19:38 CET 2007

Neal Becker wrote:

Instead, bool fails in the worst possible way: it silently gives a wrong result.

I disagree with the word "fail" there; Python is working correctly. The behavior of converting expressions to a boolean is well-defined: http://docs.python.org/ref/Booleans.html Perhaps the behavior is unexpected or unwelcome--but it is correct.
It's just one of those things about Python that one has to get used to; this is a side-effect of another, much more important principle.

If you really want to turn the string "True" into True, use "eval". eval("4") -> 4 eval("True") -> True eval("{}") -> {} Perhaps it would be safest to cast the output of eval to bool: bool(eval("True")) -> True bool(eval("")) -> False

Cheers,

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