Python module for basic I/O operations

myio.py

def read(filename):
    '''
    Opens a file and prints its lines in the console.
    Takes 1 arg (string): filename
    '''
    with open(filename) as f:
        for line in f:
            print(line.rstrip())

def add(filename, text):
    '''
    Opens a file and adds the text to the end.
    Takes 2 args (strings): filename, text to add
    '''
    with open(filename, 'a') as f:
        f.write(text)

def write(filename, text):
    '''
    Opens a file and writes the string in it.
    CAUTION: Overwrites content!
    Takes 2 args (strings): filename, text to write
    '''
    with open(filename, 'w') as f:
        f.write(text + '\n')

def chars(filename):
    '''
    Counts characters in file.
    Takes 1 arg (string): filename
    '''
    count = 0
    with open(filename) as f:
        for line in f:
            count += len(line)
    print(count)

if __name__ == '__main__':
    def do():
        f = input('Enter file name: ')
        mode = input('Choose mode (r = read, a = add text, w = write, c = character count): ')
        if mode == 'r':
            read(f)
        elif mode == 'a':
            text = input('Enter text: ') + '\n'
            add(f, text)
        elif mode == 'w':
            text = input('Enter text: ') + '\n'
            write(f, text)
        elif mode == 'c':
            chars(f)
        else:
            print('Mode not recognised, please enter \'r\', \'a\', \'w\' or \'c\'.')
            do()
    do()