Using the Boolean operator in Python to do a truth test instance _python

In Python, objects of any type can be tested for truth values and are guaranteed to return TRUE or false.

The following values, regardless of type, return False in the truth test:

1.None
2.False
3. Any type of number 0, including 0,0.0,0l,0j
4. Empty sequence (sequence) or mapping (mapping) Type objects
5. For objects of user-defined types, if their classes define __NONZERO__ () or __len__ () special methods and return False or 0

For the last rule, there are a few things to note:

1. If the class does not define any of these two methods, the object truth of this type is always tested to true
2. If the class defines both __nonzero__ () and __len__ (), only the return value of __nonzero__ () is referenced

The attributes of the Boolean operator (direct copy document):

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X or Y:if x is false, then Y, else x
X and Y:if x is false, then x, else y
Not x:if X is false, then True, else false

1. Note the short-circuit characteristics of the and and OR operators
The 2.not operator either returns TRUE or returns False
The return value of the 3.and and or operators is not limited to true and false, it simply does a truth test on X or Y, and then returns one of the values (note that it is not its truth)

code example:

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s = '
s = s or ' default value '
Print S

The results of the operation are:

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Default value