"0 in [True,False]" returns True

quentel.pierre at wanadoo.fr quentel.pierre at wanadoo.fr
Tue Dec 13 11:30:01 CET 2005

Ok, I'll explain why I wanted to test if the value was a boolean

I have a program that generates HTML tags with attributes. The
principle is that
<TAG arg1="val1" arg2="val2">text</TAG>

For HTML attributes that don't have an explicit value (such as the
SELECTED attribute in OPTION) the keyword argument to the function must
have the value True

My program has a class for each tag, all derived from a generic TAG
class whose __init__ method takes the arguments :
    def __init__(self, innerHTML="", **attrs):

I have to handle differently the cases where the value is a boolean or
another type:
- if it's a boolean then if the value is True, generate the argument
name ; if the value is False, don't generate anything
- if it's not a boolean, generate arg="val". Specifically, it val is 0,
generate val = "0"

Testing with "if v:" as suggested would fail for val = 0

Anyway, I exposed my silly "if v in [True,False]" just to give my
opinion that I found confusing that
    0 in [True,False]
or (boolean type checking set aside)
    0 in [1,range(2),False,'text']

return True


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