freeCodeCamp/guide/english/python/boolean-operations/index.md

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Python Boolean Operations

or, and, not

Python Docs - Boolean Operations

These are the Boolean operations, ordered by ascending priority:

Operation | Result | Notes  
--------- | ------------------------------------ | -----  
x or y | if x is false, then y, else x | (1)  
x and y | if x is false, then x, else y | (2)  
not x | if x is false, then True, else False | (3)

Notes:

1. This is a short-circuit operator, so it only evaluates the second argument if the first one is False.
2. This is a short-circuit operator, so it only evaluates the second argument if the first one is True.
3. not has a lower priority than non-Boolean operators, so not a == b is interpreted as not (a == b), and a == not b is a syntax error.

Examples:

or:

    >>> True or False    # Short-circuited at first argument.
    True
    >>> False or True    # Second argument is evaluated.
    True
    >>> False or False   # Second argument is evaluated.
    False

and:

`` >>> True and False # Second argument is evaluated. False >>> False and True # Short-circuted at first argument. False >>> True and True # Second argument is evaluated. True

### `not`:

>>> not True
False
>>> not False
True

## Other boolean-operations:

These are other boolean operations which are not part of the Python language, you will have to define them yourself or use the boolean expression within the parenteses.

Operation	Result	Notes
nand ( not (x and y) )	if x is True, then y, else x	(1)
nor ( not (x or y) )	if x is False, then x, else y	(2)
xor ( not (not (x or y) or (x and y)) )
xnor ( not (x or y) or (x and y) )

**Notes:**

1.  This is a short-circuit operator, so it only evaluates the second argument if the first one is True.
2.  This is a short-circuit operator, so it only evaluates the second argument if the first one is False.

## Examples:

### `nand`:
#### Used in a defined way:
```python
    def nand(x, y):
        return not(x and y)

output:

    >>> nand(True, True) # Short-circuited at first argument.
    False
    >>> nand(False, True) # Second argument is evaluated.
    True
    >>> nand(True, False) # Short-circuited at first argument.
    True
    >>> nand(False, False) # Second argument is evaluated.
    True

Used in a direct way:

    if not(x and y):
        do something....

output:

    >>> not(True and True): # Short-circuited at first argument.
    False
    >>> not(True and True) # Second argument is evaluated.
    True
    >>> not(True and True) # Short-circuited at first argument.
    True
    >>> not(True and True) # Second argument is evaluated.
    True

nor:

Used in a defined way:

    def nor(x, y):
        return not(x or y)

output:

    >>> nor(True, True) # Short-circuited at first argument.
    False
    >>> nor(False, True) # Second argument is evaluated.
    False
    >>> nor(True, False) # Short-circuited at first argument.
    False
    >>> nor(False, False) # Second argument is evaluated.
    True

Used in a direct way:

    if nor(x or y):
        do something....

output:

    >>> not(True or True): # Short-circuited at first argument.
    False
    >>> not(True or True) # Second argument is evaluated.
    False
    >>> not(True or True) # Short-circuited at first argument.
    False
    >>> not(True or True) # Second argument is evaluated.
    True

xor:

Used in a defined way:

    def xor(x, y):
        return not(not(x or y) or (x and y))

output:

    >>> xor(True, True)
    False
    >>> xor(False, True)
    True
    >>> xor(True, False)
    True
    >>> xor(False, False)
    False

Used in a direct way:

    if not(not(x or y) or (x and y)):
        do something....

output:

    >>> not(not(True or True) or (True and True)): # Short-circuited at first argument.
    False
    >>> not(not(True or False) or (True and False)) # Second argument is evaluated.
    True
    >>> not(not(False or True) or (False and True)) # Short-circuited at first argument.
    True
    >>> not(not(False or False) or (False and False)) # Second argument is evaluated.
    False

xnor:

Used in a defined way:

    def xnor(x, y):
        return not(x or y) or (x and y)

output:

    >>> xnor(True, True)
    True
    >>> xnor(False, True)
    False
    >>> xnor(True, False)
    False
    >>> xnor(False, False)
    True

Used in a direct way:

    if not(x or y) or (x and y):
        do something....

output:

    >>> not(not(True or True) or (True and True)): # Short-circuited at first argument.
    True
    >>> not(not(True or False) or (True and False)) # Second argument is evaluated.
    False
    >>> not(not(False or True) or (False and True)) # Short-circuited at first argument.
    False
    >>> not(not(False or False) or (False and False)) # Second argument is evaluated.
    True