python assert in

`assert` in Python is a keyword used for debugging purposes. It allows you to test if a given condition is true, and if not, it raises an `AssertionError` exception. The syntax for using `assert` is as follows:

assert condition, message

Here, `condition` is the expression that you want to check, and `message` is an optional string that can be used to provide additional information about the assertion.

For example, let's say you have a function that calculates the square of a number:

def square(x):
    assert isinstance(x, (int, float)), "Input must be a number"
    return x ** 2

In this case, the `assert` statement checks if the input `x` is either an integer or a float. If it is not, it raises an `AssertionError` with the provided message.

You can enable or disable assertions globally by using the `-O` (optimize) command-line option when running Python. With optimization enabled, assertions are ignored.

Please note that assertions are primarily used for debugging and should not be used as a substitute for proper error handling and input validation in production code.