python往某一行行尾追增内容

示例：在PATH开头的这一行末尾添加/usr/local/mysql/bin

with open("/home/mysql/.bash_profile") as f:

    lines=f.readlines()
with open("/home/mysql/.bash_profile","w") as w:
    for l in lines:
        if(l.startswith("PATH")):
            w.write(l.replace(b" ",b":/usr/local/mysql/bin "))
        else:
            w.write(l)