Tony Power Tony Power - 1 year ago 105
Python Question

Python: Comparing empty string to False is False, why?


not ''
evaluates to
, why does
'' == False
evaluates to

For example, the "voids" of the other types (e.g. 0, 0.0) will return
when compared to

>>> 0 == False
>>> 0.0 == False


Answer Source

In the context of Boolean operations, and also when expressions are used by control flow statements, the following values are interpreted as false: False, None, numeric zero of all types, and empty strings and containers (including strings, tuples, lists, dictionaries, sets and frozensets). All other values are interpreted as true. User-defined objects can customize their truth value by providing a __bool__() method.

The operator not yields True if its argument is false, False otherwise.


The operators <, >, ==, >=, <=, and != compare the values of two objects. The objects do not need to have the same type.


Because all types are (direct or indirect) subtypes of object, they inherit the default comparison behavior from object. Types can customize their comparison behavior by implementing rich comparison methods like __lt__() ...

So, the technical implementation answer is that it behaves the way it does because not and == use different comparisons. not uses __bool__, the "truth value" of an object, while == uses __eq__, the direct comparison of one object to another. So it's possible to ask an object whether it considers itself to be truthy or falsey, and separately from that ask it whether it considers itself to be equal to another object or not. The default implementations for that are arranged in a way that two objects can both consider themselves falsey yet not consider themselves equal to one another.

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