python替换文件指定字符串

需求：将文件中的全部he替换成s

with open('/download/python_practice/a.py','r') as r:

    lines=r.readlines()
with open('/download/python_practice/a.py','w') as w:
    for l in lines:

        w.write(l.replace('he','s'))

--如若想替换某行的某个内容，需要加个if判断（注意，必须要写else，否则write替换后的行内容会完全覆盖文件之前的所有内容）：

--替换以PATH开头的那一行的内容:/usr/local/mysql/bin为空

[root@PC python_practice]# cat g.py
with open('/download/python_practice/d.py','r') as r:
    lines=r.readlines()
with open('/download/python_practice/d.py','w') as w:
    for l in lines:
       if l.startswith('PATH'):
           w.write(l.replace(':/usr/local/mysql/bin',''))
       else:
           w.write(l)