Python Reuse a Variable in the Else Block of an If-Else Statement

I'm currently working on a simple file transfer program in Python. I am having trouble with the function for prompting the user for the location of the folder to be copied.

def getSrc():
    if getSrc.has_been_called is False:
        source = askdirectory()
        getSrc.has_been_called = True
        return source
    else:
        return source

getSrc.has_been_called = False

The variable source comes up as an unresolved reference. I understand that the variable must be initialized again due to the scope of an if-else statement, but I am unsure of how to save the directory in the source variable without the user being prompted for the directory again.