Python or Operator
Summary: in this tutorial, you’ll learn about the Python or
operator and how to use it effectively.
Introduction to the Python or
operator
The or
the operator is a logical operator. Typically, you use the or
operator to combine two Boolean expressions and return a Boolean value.
The or
the operator returns True
if one of the two operands is True
. And it returns False
only if both operands are False
.
This truth table displays the result of the or
operator:
x | y | x or y |
---|---|---|
True | True | True |
True | False | True |
False | True | True |
False | False | False |
The following example shows how to use the or
operator:
is_admin = False
is_editor = True
can_edit = is_admin or is_editorprint(can_edit)
Code language: PHP (php)
Output:
True
Code language: PHP (php)
The Python or operator is short-circuiting
When evaluating an expression that involves the or
operator, Python can sometimes determine the result without evaluating all the operands. This is called short-circuit evaluation or lazy evaluation.
For example:
x or y
If x
is truthy, then the or
operator returns x
. Otherwise, it returns y
.
In other words, if x
is truthy, then the or
operator doesn’t need to evaluate y
. It just returns x
immediately. This is why the evaluation is called lazy or short-circuiting evaluation.
The or
operator only evaluates y
and returns the result of the evaluation if x
is falsy.
In Python, every object associates with a Boolean value. And the x
and y
can be any object.
This opens some useful applications of the or
operator.
Setting a default value for a variable
The or
operator allows you to set a default value for a variable, for example:
var_name = value or default
Code language: JavaScript (javascript)
In this example, if value
is falsy, the or
operator return the default
.
The following example prompts you for input. If you don’t enter anything, the lang
will default to 'Python'
:
lang = input('Enter your language:') or 'Python'
print(lang)
Code language: PHP (php)
The following example defines a function get_data()
that returns a list of numbers. It uses the built-in min()
function to find the lowest element in the list:
def get_data(args=None):
if args:
return [1, 2, 3]
return []lowest = min(get_data(args=true))
print(lowest)
Code language: PHP (php)
Output:
1
It returned 1 as expected. However, the get_data()
may return an empty list like this:
lowest = min(get_data())
print(lowest)
Code language: PHP (php)
It returned a ValueError
.
To fix this, you can use the or
operator when calling the min()
function:
def get_data(args=None):
if args:
return [1, 2, 3]
return []lowest = min(get_data() or [0])
print(lowest)
Code language: PHP (php)
Output:
0
In this example, if the get_data() function returns an empty list, the or
operator will treat its result as a falsy value.
Since the first operand is falsy, the or
operator needs to evaluate the second operand [0]
. In this case, you can specify the default minimum value in the second operand.