Is there some kind of keyword to use in Python, that can be logically compared to always be false?
For example, I want something like
None > 20
To return false when evaluated. Is there some keyword to use besides None here, since comparing a NoneType and Integer throws an error?
I don't think there's a built-in object that does this, but you can always make your own:
class Thing:
def __lt__(self, other):
return False
#use the same function for <=, ==, >, etc
__le__ = __eq__ = __gt__ = __ge__ = __lt__
x = Thing()
print(x < 20)
print(x <= 20)
print(x > 20)
print(x >= 20)
print(x == 20)
Result:
False
False
False
False
False
Edit: I remembered a built-in way to do this. If you only need to compare to ordinary numbers, you can use the special "Not a Number" floating point value:
x = float("nan")
print(x < 20)
print(x <= 20)
print(x > 20)
print(x >= 20)
print(x == 20)
Result:
False
False
False
False
False
And if you specifically only want x > 20 to return False and don't particularly care what the other comparisons return, it may make more sense to use the special "negative infinity" floating point value.
>>> x = float("-inf")
>>> x > 20
False
float("nan") != 20
float("nan") != 20 evaluates to True. Looks like you'll have to define your own type after all. (don't forget to add __ne__ to the __le__ = __eq__ = ... chain)
Noneif some condition is met. Later, I am usingevalto evaluate some boolean logic, which then goes and tries to compareNone > 20(or some other number). I actually got around this by putting eval in a try/except block, and passing the TypeError, but I'm not sure if that is the best way to do this.