version：Python 3.3.2
Python用open()返回一个文件，最常用的open函数是open(filename , mode)
其中，mode包括有"w"(write)， “r”(read) ， “a”(open the file for appending)， 当然也可以用“wt”表示写入text，“rt”表示读取text；
file.readline()可以一次读取文件中内容的一行
* 每次文件操作完成之后，一定要加上file.close()函数将文件关闭。
>>> strings = """\I'm a great man who was born in China I was born to give and give and give This is a new line And this is another new line""" >>> file.write(strings) 123 #此处表示写入的内容总共有多少byte >>> file.close()
我们可以调用read()函数将文件的内容打印出来，但是当read()之后，当前的位置将停留在末尾也就是文字的最后位置，如果这时候想再次打印文件内容，调用read()函数将得到空的内容，可行的办法之一是将文件关闭再重新打开，当然我们也有一些新的办法来简化此操作。
>>> file = open("output.txt","rt")
>>> print(file.read())
\I'm a great man who was born in China
I was born to give and give and give
This is a new line
And this is another new line
>>> print(file.read())
#这里将会是空白，因为此刻指针（光标）的位置处于段落末尾
1. seek()
seek可以用来改变当前object的位置（例如file read之后），通常的格式seek(offset, from_what)。
The position is computed from adding offset to a reference point; the reference point is selected by the from_what argument. A from_what value of 0 measures from the beginning of the file, 1 uses the current file position, and 2 uses the end of the file as the reference point. from_what can be omitted and defaults to 0, using the beginning of the file as the reference point.
默认只有一个参数，就表示从文件开始的位置(0)，因此，seek(0)就表示目前是处于文件的开头，第二个参数表示从哪里开始计算，0表示开头，也是默认的，1表示当前位置，2表示末尾。
>>> file.seek(0) 0#当前位置 >>> print(file.read()) \I'm a great man who was born in China I was born to give and give and give This is a new line And this is another new line
2. 利用list，将file中的文字存入到list中
file有一个函数readlines()，注意此函数和readline()有区别，readline是一次读取一行，而readlines()是将所有数据存入list中，每一行作为list的一个element，如此之后，即便我们close的文件，依旧可以继续打印文件里已经存储在list中的内容了。
>>> x = file.readlines()#错误，注意此时的位置已经处于末尾了
>>> print(x)
[]#所以打印出来的内容为空
>>> print(x[0])
Traceback (most recent call last):
File "<pyshell#7>", line 1, in <module>
print(x[0])
IndexError: list index out of range
>>> file.seek(0)#将位置置于开头
0
>>> x = file.readlines()
>>> print(x)
["\\I'm a great man who was born in China\n", 'I was born to give and give and give\n', 'This is a new line\n', 'And this is another new line']
>>> print(x[0])#打印list的各项内容
\I'm a great man who was born in China
>>> file.close()#即便关闭了file，也可以继续操作，因为内容已经存储到了list中
>>> print(x[0])
\I'm a great man who was born in China
>>> print(x[3])
And this is another new line
>>> 代码中我犯了一个错误，第一次没有将位置seek到开头，所以第一次没有将lines存入到x中，也就是说，若想把每一行存入到list中，也需要将当前位置置于0
