global variable and local variable

out_list = ['I am the outlist']

def case1():
    # out_list is the global varible because it is not assigned in
    # the function. It is only referenced
    out_list.append('modified in case2')
    print('in-case1 print: %s' % out_list)
    return


def case2():
    # can not use (reference) un-defined variable
    inner_list.append('added in case2')
    print('in-case2 print: %s' % inner_list)
    return


def case3():
    # out_list is a local variable here because is assigned
    out_list = []
    out_list.append('modified in case4')
    print('in-case4 print: %s' % out_list)
    return
    

def case4():
    # explictly use out_list
    global out_list
    out_list.append('modified in case3')
    print('in-case3 print: %s' % out_list)
    return


def case5():
    # interestingly, if out_list appears somewhere in function,
    # it is treated as a local variable
    # This, is because when python is parsing fucntions, it will find
    # all the assignment in this function (like out_list = []), if there
    # is one, this variable will be treated as local variable
    out_list.append('modified in case5')
    print('in-case5 print: %s' % out_list)
    out_list = []
    out_list.append('modified in case5')
    print('in-case5 print: %s' % out_list)
    return


def case6():
    # use global and assign in function again
    global out_list
    out_list.append('modified in case5')
    print('in-case6 print: %s' % out_list)
    out_list = []
    out_list.append('modified in case5')
    print('in-case6 print: %s' % out_list)
    return


def case7():
    # use global before assignment, the varible is a global variable now!
    # then you can print inner_list outside the function
    global inner_list
    inner_list = []
    inner_list.append('modified in case7')
    return


if __name__ == '__main__':
    case1()
    print('out-function print: %s' % out_list)