open()成功执行后返回一个文件对象，以后所有对该文件的操作都可以通过这个“句柄”来进行，现在主要讨论下常用的输入以及输出操作。
输出：
read()方法用于直接读取字节到字符串中，可以接参数给定最多读取的字节数，如果没有给定，则文件读取到末尾。文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
readline()方法读取打开文件的一行(读取下个行结束符之前的所有字节)，然后整行，包括行结束符，作为字符串返回。文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
readlines()方法读取所有行然后把它们作为一个字符串列表返回文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
eg：文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
文件/root/2.txt的内容如下，分别使用上面的三个方法来读取，注意区别：文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
read():
cat /root/2.txt文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
I'll write this message for you
hehe,that's will be ok.文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
>>>>fobj = open('/root/2.txt') ##默认已只读方式打开文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
>>>>a = fobj.read()文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
>>>>a文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
"I'll write this message for you\nhehe,that's will be ok.\n" ##直接读取字节到字符串中,包括了换行符文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
>>>> print a文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
I'll write this message for you
hehe,that's will be ok.文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
>>>>fobj.close() ##关闭打开的文件文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
readline():
>>>> fobj = open('/root/2.txt')文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
>>>>b = fobj.readline()文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
>>>>b文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
"I'll write this message for you\n" ##整行，包括行结束符，作为字符串返回文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
>>>>c = fobj.readline()文章源自运维生存时间-https://www.ttlsa.com/python/python-read-readline-readlines-write-writelines/
c
>>>>"hehe,that's will be ok.\n" ##整行，包括行结束符，作为字符串返回
>>>>fobj.close()
readlines():
>>>>fobj = open('/root/2.txt')
>>>> d = fobj.readlines()
>>>>d
["I'll write this message for you\n", "hehe,that's will be ok.\n"] ##读取所有行然后把它们作为一个字符串列表返回
>>>>fobj.close()
输入：
write()方法和read()、readline()方法相反，将字符串写入到文件中。
和readlines()方法一样，writelines()方法是针对列表的操作。它接收一个字符串列表作为参数，将他们写入到文件中，换行符不会自动的加入，因此，需要显式的加入换行符。
eg:
write():
>>> >fobj = open('/root/3.txt','w') ###确保/root/3.txt没有存在，如果存在，则会首先清空，然后写入。
>>> >msg = ['write date','to 3.txt','finish'] ###这里没有显式的给出换行符
>>> >for m in msg:
... fobj.write(m)
...
>>> >fobj.close()
cat /root/3.txt
write dateto 3.txtfinish
>>>>fobj = open('/root/3.txt','w') ###覆盖之前的数据
>>>>msg = ['write date\n','to 3.txt\n','finish\n'] ###显式给出换行符
>>> >for m in msg:
... fobj.write(m)
...
>>> >fobj.close()
cat /root/3.txt
write date
to 3.txt
finish
writelines():
>>>>fobj = open('/root/3.txt','w')
>>>>msg = ['write date\n','to 3.txt\n','finish\n']
>>>>fobj.writelines(msg)
>>>>fobj.close()
cat /root/3.txt
write date
to 3.txt
finish
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