import re

if __name__ == "__main__":
    text = "yeah, but no, but yeah, but no, but yeah"

    # 简单的替换可以使用replace函数来完成
    text_change = text.replace('yeah', 'yep')
    print(text_change)

    # 对复杂的替换，我们可以使用re.sub模块
    text = "Today is 11/27/2012. PyCon starts 3/12/2013"
    text_change = re.sub(r'(\d+)/(\d+)/(\d+)', r'\3-\1-\2', text)
    print(text_change)

    # 如果需要多次替换，记得先编译再sub
    datepat = re.compile(r'(\d+)/(\d+)/(\d+)')
    print(datepat.sub(r'\3-\1-\2', text))

    # 想要知道完成了几次替换，可以使用subn
    # subn返回一个元组，结构为（替换后的字符串， 替换次数）
    print(datepat.subn(r'\3-\1-\2', text))