7.3. The assert statement
What is the use of “assert” in Python?
Assert statements are a convenient way to insert debugging assertions into a program.
Source code: python-code/toolkit/start_assert.py
assert expression, "AssertionError message."
equivalent to,
if __debug__:
if not expression: raise AssertionError("message.")
where __debug__ is built-in variable with True value.
print(f"__debug__ = {__debug__}. If __debug__ is False, it will not raise any AssertionError.")
Ex.1
First example, check two values are equal or not:
assert 0 == 1, "hello, 0 is not equal to 1 !"
this output will be:
AssertionError
Traceback (most recent call last)
c:\Users\user\Desktop\san\python-code\start_assert.py in
----> 20 assert 0 == 1, "hello, 0 is not equal to 1 !"
AssertionError: hello, 0 is not equal to 1 !
Ex.2
Alert the input number should be positive number:
number = int(input("Enter a number:"))
assert number > 0, "Only positive number is allowed."
Ex.2.1
same as Ex.2, to show f-string functionality can be used in assert:
number = int(input("Enter a number:"))
assert number > 0, f"Is number <= 0 ? {number <= 0}"
Ex.3
Check the class of object df as we thounght:
#import pandas as pd
#df = pd.DataFrame(data = list(range(10)), columns= ['number'])
df = list(range(10))
assert isinstance(df, pd.DataFrame), "df is not a pd.DataFrame."