What does the '-=' operator do in Python?

The '-=' operator in Python is a shorthand for subtracting a value from a variable and then reassigning that updated value back to the variable. For example, if you have a variable x with a value of 10 and you execute x -= 3, it would subtract 3 from 10 and then store the result (which is 7) back in x. This operator is effectively a combination of subtraction and assignment, allowing for more concise and readable code.

This makes it particularly useful in loops or scenarios where you want to decrease a value iteratively without having to write the full expression each time. The operator simplifies code and helps in making it less prone to errors by reducing the repetition of variable names.

The other options describe different operators that do not reflect the functionality of the '-=' operator. This reinforces the understanding that '-=' specifically deals with subtraction and reassignment, which is distinct from the operations represented by the other choices.