Python assert keyword

Python assert keyword is used (in the debugging tool) while debugging programs that test a condition. The assert statement has a condition or expression which is supposed to be always true. If the condition is false assert halts the program and gives an AssertionError.

assert <condition>

Or

assert <condition>,<error message>

Python assert keyword

A simple example code test is if a condition in code returns True, if not, the program will raise an AssertionError.

x = "hello"

# if True, then nothing happens:
assert x == "hello"

# if False, AssertionError is raised:
assert x == "goodbye"

Output:

Using assert without Error Message

def avg(marks):
    assert len(marks) != 0
    return sum(marks) / len(marks)


mark1 = []
print("Average of mark1:", avg(mark1))

Using assert with an error message

def avg(marks):
    assert len(marks) != 0,"List is empty."
    return sum(marks)/len(marks)

mark2 = [55,88,78,90,79]
print("Average of mark2:",avg(mark2))

mark1 = []
print("Average of mark1:",avg(mark1))

Do comment if you have any doubts or suggestions on this Python Keyword topic.

Note: IDE: PyCharm 2021.3.3 (Community Edition)

Windows 10

Python 3.10.1

All Python Examples are in Python 3, so Maybe its different from python 2 or upgraded versions.