python字符串replace()方法

>>> help(str.replace)

Help on method_descriptor:

replace(...)

    S.replace(old, new[, count]) -> string

    

    Return a copy of string S with all occurrences of substring

    old replaced by new.  If the optional argument count is

    given, only the first count occurrences are replaced.

>>> s='hello python,hello world,hello c++,hello java!'

>>> s.replace('hello','Hello')#将字符串s中的所有'hello'子串，替换成'Hello',返回替换后的字符串，原字符串s不变

'Hello python,Hello world,Hello c++,Hello java!'

>>> s

'hello python,hello world,hello c++,hello java!'

>>> s.replace('hello','Hello',2)#将字符串s中的前2个'hello'子串，替换成'Hello'

'Hello python,Hello world,hello c++,hello java!'

>>> s

'hello python,hello world,hello c++,hello java!'

>>> s.replace('wahaha','haha')#要替换的'wahaha'子串不存在，直接返回原字符串

'hello python,hello world,hello c++,hello java!'