Assert Statement in Python

What is Assertion?

In any programming language, assertions are the debugging tools that aid in the efficient operation of the code. Assumptions are primarily statements that a programmer knows to be true or always wants to be true and include in code so that if they are false, the code cannot continue to run.

Assert Statement in Python:

If the supplied condition evaluates to True in Python, the assert statement is used to continue the execution. The assert condition raises the AssertionError exception with the supplied error message if it evaluates to False.

Syntax :

assert condition, error_message(optional)

where,

• condition : The boolean condition returning true or false. 
• error_message : The optional argument to be printed in the console in case of AssertionError

Example:

The following example demonstrates a simple assert statement.

x = 10
assert x > 0
print('x is a positive number.')

Output:

x is a positive number.

In the above illustration, the assert condition, x > 0, evaluates to True, allowing the next statement to be executed without any errors.

Example:

Python assert keyword with error message.

x = 0
assert x > 0, 'Only positive numbers are allowed'
print('x is a positive number.')

Output:

Traceback (most recent call last):
    assert x > 0, 'Only positive numbers are allowed'
AssertionError: Only positive numbers are allowed

Important points to remember:

• The major purpose of assertions is debugging.
• Assertions’ main purpose is to set up alarms if a programme bug manifests itself.
• Assertions can be used to test preconditions and postconditions in your programmes while they are still in development.
• It is evident from assertions that you want to determine whether a particular condition is true and will continue true.
• In your code, assertions are also great for constructing test cases.
• Assertions are not an error-handling mechanism.

Note: also read about @property Decorator in Python

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