assert python

1"""Quick note!
2This code snippet has been copied by Pseudo Balls.
3This is the original answer.
4Please consider justice by ignoring his answer.
5"""
6"""assert:
7evaluates an expression and raises AssertionError
8if expression returns False
9"""
10assert 1 == 1  # does not raise an error
11assert False  # raises AssertionError
12# gives an error with a message as provided in the second argument
13assert 1 + 1 == 3, "1 + 1 does not equal 3"
14"""When line 7 is run:
15AssertionError: 1 + 1 does not equal 3
16"""

1assert <condition>,<error message>
2#The assert condition must always be True, else it will stop execution and return the error message in the second argument
3assert 1==2 , "Not True" #returns 'Not True' as Assertion Error.

1In simple words, if the assert condition is true then the
2program control will execute the next test step but if the condition is
3false, the execution will stop and further test step will not be executed.
4

1x = "hello"
2
3#if condition returns False, AssertionError is raised:
4assert x == "goodbye", "x should be 'hello'"
5-----------------------------------------------------------------
6Traceback (most recent call last):
7  File "demo_ref_keyword_assert2.py", line 4, in <module>
8    assert x == "goodbye", "x should be 'hello'"
9AssertionError: x should be 'hello'

1name = 'quaid'
2# check if name assigned is what assert expects else raise exception
3assert(name == 'sam'), f'name is {name}, it should be sam'
4
5print("Hello {check_name}".format(check_name = name))
6#output: Assertion Error 
7# quaid is not what assert expects rather it expects sam as a string assigned to name variable
8# No print out is received

1def input_age(age):
2   try:
3       assert int(age) > 18
4   except ValueError:
5       return 'ValueError: Cannot convert into int'
6   else:
7       return 'Age is saved successfully'
8 
9print(input_age('23'))  	# This will print
10print(input_age(25))  		# This will print
11print(input_age('nothing')) # This will raise ValueError which is handled
12print(input_age('18'))  	# This will raise AssertionError, program collapses
13print(input_age(43))  		# This won't print