Boolean Operators

and

Evaluates to the second argument if and only if both of the arguments are truthy. Otherwise evaluates to the first falsey argument.

x = True
y = True
z = x and y # z = True

x = True
y = False
z = x and y # z = False

x = False
y = True
z = x and y # z = False

x = False
y = False
z = x and y # z = False

x = 1
y = 1
z = x and y # z = y, so z = 1, see `and` and `or` are not guaranteed to be a boolean

x = 0
y = 1
z = x and y # z = x, so z = 0 (see above)

x = 1
y = 0
z = x and y # z = y, so z = 0 (see above)

x = 0
y = 0
z = x and y # z = x, so z = 0 (see above)

The 1’s in the above example can be changed to any truthy value, and the 0’s can be changed to any falsey value.

or

Evaluates to the first truthy argument if either one of the arguments is truthy. If both arguments are falsey, evaluates to the second argument.

x = True
y = True
z = x or y # z = True

x = True
y = False
z = x or y # z = True

x = False
y = True
z = x or y # z = True

x = False
y = False
z = x or y # z = False

x = 1
y = 1
z = x or y # z = x, so z = 1, see `and` and `or` are not guaranteed to be a boolean

x = 1
y = 0
z = x or y # z = x, so z = 1 (see above)

x = 0
y = 1
z = x or y # z = y, so z = 1 (see above)

x = 0
y = 0
z = x or y # z = y, so z = 0 (see above)

The 1’s in the above example can be changed to any truthy value, and the 0’s can be changed to any falsey value.

not

It returns the opposite of the following statement:

x = True
y = not x # y = False

x = False
y = not x # y = True

Short-circuit evaluation

Python minimally evaluates Boolean expressions.

>>> def true_func():
...     print("true_func()")
...     return True
... 
>>> def false_func():
...     print("false_func()")
...     return False
... 
>>> true_func() or false_func()
true_func()
True
>>> false_func() or true_func()
false_func()
true_func()
True
>>> true_func() and false_func()
true_func()
false_func()
False
>>> false_func() and false_func()
false_func()
False

`and` and `or` are not guaranteed to return a boolean

When you use or, it will either return the first value in the expression if it’s true, else it will blindly return the second value. I.e. or is equivalent to:

def or_(a, b):
    if a:
        return a
    else:
        return b

For and, it will return its first value if it’s false, else it returns the last value:

def and_(a, b):
    if not a:
        return a
    else:
        return b

and

or

not

Short-circuit evaluation

and and or are not guaranteed to return a boolean

A simple example

`and` and `or` are not guaranteed to return a boolean