for j in range(3): IndentationError: unexpected indent

This error occurs when there is an unexpected indentation in the code. It means that the Python interpreter was expecting the code to be at a certain level of indentation but found it at a different level.

To fix this error, make sure that all lines of code within the same block have the same level of indentation. In this specific example, the code block containing the for loop should have the same level of indentation for all lines within the loop.

Here is an example of correct indentation for the for loop:

for j in range(3):
    # code goes here

Notice how the second line is indented by four spaces. This is the standard indentation level in Python, but you can also use a tab character or any number of spaces as long as it is consistent throughout the code.