assert in python

`assert` is a keyword in Python that is used to check if a condition is true, and if it's not true, it raises an `AssertionError`. The syntax for using `assert` is:

assert condition, message

`condition` is the expression that is being tested, and `message` is an optional string that will be displayed if the assertion fails.

For example:

x = 5
assert x == 5, "x should be 5"

This code will run without error, because the condition `x == 5` is true. However, if we change `x` to a different value and run the code again:

x = 10
assert x == 5, "x should be 5"

It will raise an `AssertionError` with the message "x should be 5". This can be helpful for debugging and testing purposes.