> Compare with the if statement, where the variable in the expression being tested will necessarily be defined.

    if False:
        x = 7
    print(x)

    print(x)
          ^
    NameError: name 'x' is not defined

Ruby does this sort of stuff, where a variable is defined more or less lexically (nil by default). Python doesn't do this. You can have local variables that only maybe exist in Python.