Assertion in Python Programming

Hello dear readers! welcome back to another section of my tutorial on Python. In this tutorial post, we will be studying about Assertions in Python.

What is an Assertion?

The easiest way to think of an assertion is to link it to a raise-if statement (or to be more accurate, a raise-if-not statement). An expression is tested and if the result comes up false, then an exception is raised.

Assertions in Python are carried out by the assert statement, the newest keyword to Python, it was introduced in version 1.5

Python programmers often place assertions at the start of a function to check for valid input, and after a function call to check for valid output.

When an assert statement is being encountered, Python evaluates the accompanying expression, which is hopefully true. If the expression is false, then an AssertionError exception is raised by Python.

Syntax

assert Expression[, Arguments]

If the assertion fails, Python uses ArgumentExpression as the code argument for the AssertionError. The AssertionError exceptions can be of course caught and handled like any other exception using the try-except statement, but if it is not handled, they will then terminate the program and then produce a traceback.

Example

#!/usr/bin/python

def KelvinToFahrenheit(Temperature):
assert (Temperature >= 0),"Colder than absolute zero!"
return ((Temperature-273)*1.8)+32

print KelvinToFahrenheit(273)
print int(KelvinToFahrenheit(505.78))
print KelvinToFahrenheit(-5)

Output

32.0 451 Traceback (most recent call last): File "test.py", line 9, in <module> print KelvinToFahrenheit(-5) File "test.py", line 4, in KelvinToFahrenheit assert (Temperature >= 0),"Colder than absolute zero!" AssertionError: Colder than absolute zero!

Alright guys! This is where we are rounding up for this tutorial post. In my next tutorial, we are going to be discussing about the Object Oriented Programming in Python.

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