>你这论断人的，无论你是谁，也无可推诿，你在甚么事上论断人，就在甚么事上定自己的罪。因你这论断人的，自己所行却和别人一样。我们知道这样行的人，神必照真理审判他。(ROMANS 2:1-2)
#文件(2)
文件，也是对象。
在Python 2中还是一种内建的类型，在Python 3中被取消了，可是，这并不意味这其地位降低。
##文件的状态
很多时候，我们需要获取一个文件的有关状态（也称为属性），比如创建日期，访问日期，修改日期，大小，等等。在os模块中，有这样一个方法，专门让我们查看文件的这些状态参数的。
>>> import os
>>> file_stat = os.stat("131.txt") #查看这个文件的状态
>>> file_stat #文件状态是这样的。从下面的内容，有不少从英文单词中可以猜测出来。
posix.stat_result(st_mode=33204, st_ino=5772566L, st_dev=2049L, st_nlink=1, st_uid=1000, st_gid=1000, st_size=69L, st_atime=1407897031, st_mtime=1407734600, st_ctime=1407734600)
>>> file_stat.st_ctime #这个是文件创建时间
1407734600.0882277
这是什么时间？看不懂！别着急，换一种方式。在Python中，有一个模块`time`，是专门针对时间设计的。
>>> import time
>>> time.localtime(file_stat.st_ctime) #这回看清楚了。
time.struct_time(tm_year=2014, tm_mon=8, tm_mday=11, tm_hour=13, tm_min=23, tm_sec=20, tm_wday=0, tm_yday=223, tm_isdst=0)
##read/readline/readlines
用`open()`能够打开文件，在用for循环，可以将文件的内容读取出来。
但是，在查看文件的属性和方法的时候，会看到三个方法：`read, readline, readlines`。
从名称上看，它们应该都是跟“读”有关的，但是，又应该有差别。
的确如此。
还是对比着看一看，并且还要Python 2和Python 3的文档对比。
Python 2：
>>> help(file.read)
Help on method_descriptor:
read(...)
read([size]) -> read at most size bytes, returned as a string.
If the size argument is negative or omitted, read until EOF is reached.
Notice that when in non-blocking mode, less data than what was requested
may be returned, even if no size parameter was given.
>>> help(file.readline)
Help on method_descriptor:
readline(...)
readline([size]) -> next line from the file, as a string.
Retain newline. A non-negative size argument limits the maximum
number of bytes to return (an incomplete line may be returned then).
Return an empty string at EOF.
>>> help(file.readlines)
Help on method_descriptor:
readlines(...)
readlines([size]) -> list of strings, each a line from the file.
Call readline() repeatedly and return a list of the lines so read.
The optional size argument, if given, is an approximate bound on the
total number of bytes in the lines returned.
Python 3：
>>> f = open("130.txt")
>>> help(f.read)
Help on built-in function read:
read(size=-1, /) method of _io.TextIOWrapper instance
Read at most n characters from stream.
Read from underlying buffer until we have n characters or we hit EOF.
If n is negative or omitted, read until EOF.
>>> help(f.readline)
Help on built-in function readline:
readline(size=-1, /) method of _io.TextIOWrapper instance
Read until newline or EOF.
Returns an empty string if EOF is hit immediately.
>>> help(f.readlines)
Help on built-in function readlines:
readlines(hint=-1, /) method of _io.TextIOWrapper instance
Return a list of lines from the stream.
hint can be specified to control the number of lines read: no more
lines will be read if the total size (in bytes/characters) of all
lines so far exceeds hint.
对照一下上面的说明，三个的异同就显现了。而且，要想了解Python 2和Python 3之间的不同，还可以将两个版本的对照一下。好像也没有什么不同哦。
EOF什么意思？End-of-file。在[维基百科](http://en.wikipedia.org/wiki/End-of-file)中居然有对它的解释：
In computing, End Of File (commonly abbreviated EOF[1]) is a condition in a computer operating system where no more data can be read from a data source. The data source is usually called a file or stream. In general, the EOF is either determined when the reader returns null as seen in Java's BufferedReader,[2] or sometimes people will manually insert an EOF character of their choosing to signal when the file has ended.
明白EOF之后，就对比一下：
- read：如果指定了参数size，就按照该指定长度从文件中读取内容，否则，就读取全文。被读出来的内容，全部塞到一个字符串里面。这样有好处，就是东西都到内存里面了，随时取用，比较快捷；“成也萧何败萧何”，也是因为这点，如果文件内容太多了，内存会吃不消的。文档中已经提醒注意在“non-blocking”模式下的问题，关于这个问题，不是本节的重点，暂时不讨论。
- readline：那个可选参数size的含义同上。它则是以行为单位返回字符串，也就是每次读一行，依次循环，如果不限定size，直到最后一个返回的是空字符串，意味着到文件末尾了(EOF)。
- readlines：size同上。它返回的是以行为单位的列表，即相当于先执行`readline()`，得到每一行，然后把这一行的字符串作为列表中的元素塞到一个列表中，最后将此列表返回。
依次演示操作，即可明了。有这样一个文档，名曰：you.md，其内容和基本格式如下：
You Raise Me Up
When I am down and, oh my soul, so weary;
When troubles come and my heart burdened be;
Then, I am still and wait here in the silence,
Until you come and sit awhile with me.
You raise me up, so I can stand on mountains;
You raise me up, to walk on stormy seas;
I am strong, when I am on your shoulders;
You raise me up: To more than I can be.
分别用上述三种函数读取这个文件。
>>> f = open("you.md")
>>> content = f.read()
>>> content
'You Raise Me Up\nWhen I am down and, oh my soul, so weary;\nWhen troubles come and my heart burdened be;\nThen, I am still and wait here in the silence,\nUntil you come and sit awhile with me.\nYou raise me up, so I can stand on mountains;\nYou raise me up, to walk on stormy seas;\nI am strong, when I am on your shoulders;\nYou raise me up: To more than I can be.\n'
>>> f.close()
**提示：养成一个好习惯，**只要打开文件，不用该文件了，就一定要随手关闭它。
>注意：在python中，'\n'表示换行，这也是UNIX系统中的规范。但是，在奇葩的windows中，用'\r\n'表示换行。Python在处理这个的时候，会自动将'\r\n'转换为'\n'。
请仔细观察，得到的就是一个大大的字符串，但是这个字符串里面包含着一些符号`\n`，因为原文中有换行符。如果用print输出这个字符串，就是这样的了，其中的`\n`起作用了。
>>> print content #Python 3: print(content)
You Raise Me Up
When I am down and, oh my soul, so weary;
When troubles come and my heart burdened be;
Then, I am still and wait here in the silence,
Until you come and sit awhile with me.
You raise me up, so I can stand on mountains;
You raise me up, to walk on stormy seas;
I am strong, when I am on your shoulders;
You raise me up: To more than I can be.
用`readline()`读取，则是这样的：
>>> f = open("you.md")
>>> f.readline()
'You Raise Me Up\n'
>>> f.readline()
'When I am down and, oh my soul, so weary;\n'
>>> f.readline()
'When troubles come and my heart burdened be;\n'
>>> f.close()
显示出一行一行读取了，每操作一次`f.readline()`，就读取一行，并且将指针向下移动一行，如此循环。显然，这种是一种循环，或者说可迭代的。因此，就可以用循环语句来完成对全文的读取。
#!/usr/bin/env python
# coding=utf-8
f = open("you.md")
while True:
line = f.readline()
if not line: #到EOF，返回空字符串，则终止循环
break
print line , #Python 3: print(line, end='')
f.close() #别忘记关闭文件
将其和文件"you.md"保存在同一个目录中，我这里命名的文件名是12701.py，然后在该目录中运行`python 12701.py`，就看到下面的效果了：
~/Documents$ python 12701.py
You Raise Me Up
When I am down and, oh my soul, so weary;
When troubles come and my heart burdened be;
Then, I am still and wait here in the silence,
Until you come and sit awhile with me.
You raise me up, so I can stand on mountains;
You raise me up, to walk on stormy seas;
I am strong, when I am on your shoulders;
You raise me up: To more than I can be.
也用`readlines()`来读取此文件：
>>> f = open("you.md")
>>> content = f.readlines()
>>> content
['You Raise Me Up\n', 'When I am down and, oh my soul, so weary;\n', 'When troubles come and my heart burdened be;\n', 'Then, I am still and wait here in the silence,\n', 'Until you come and sit awhile with me.\n', 'You raise me up, so I can stand on mountains;\n', 'You raise me up, to walk on stormy seas;\n', 'I am strong, when I am on your shoulders;\n', 'You raise me up: To more than I can be.\n']
返回的是一个列表，列表中每个元素都是一个字符串，每个字符串中的内容就是文件的一行文字，含行末的符号。显而易见，它是可以用for来循环的。
>>> for line in content:
... print line , #Python 3: print(line, end='')
...
You Raise Me Up
When I am down and, oh my soul, so weary;
When troubles come and my heart burdened be;
Then, I am still and wait here in the silence,
Until you come and sit awhile with me.
You raise me up, so I can stand on mountains;
You raise me up, to walk on stormy seas;
I am strong, when I am on your shoulders;
You raise me up: To more than I can be.
>>> f.close()
##读很大的文件
前面已经说明了，如果文件太大，就不能用`read()`或者`readlines()`一次性将全部内容读入内存，可以使用while循环和`readline()`来完成这个任务。
此外，还有一个方法：`fileinput`模块
>>> import fileinput
>>> for line in fileinput.input("you.md"):
... print line , #Python 3: print(line, end='')
...
You Raise Me Up
When I am down and, oh my soul, so weary;
When troubles come and my heart burdened be;
Then, I am still and wait here in the silence,
Until you come and sit awhile with me.
You raise me up, so I can stand on mountains;
You raise me up, to walk on stormy seas;
I am strong, when I am on your shoulders;
You raise me up: To more than I can be.
我比较喜欢这个，用起来是那么得心应手，简洁明快，还用for。
对于这个模块的更多内容，读者可以自己在交互模式下利用`dir()`，`help()`去查看明白。
还有一种方法，更为常用：
>>> for line in f:
... print line , #Python 3: print(line, end='')
...
You Raise Me Up
When I am down and, oh my soul, so weary;
When troubles come and my heart burdened be;
Then, I am still and wait here in the silence,
Until you come and sit awhile with me.
You raise me up, so I can stand on mountains;
You raise me up, to walk on stormy seas;
I am strong, when I am on your shoulders;
You raise me up: To more than I can be.
之所以能够如此，是因为文件是可迭代的对象，直接用for来迭代即可。
##seek
这个函数的功能就是让指针移动。比如：
>>> f = open("you.md")
>>> f.readline()
'You Raise Me Up\n'
>>> f.readline()
'When I am down and, oh my soul, so weary;\n'
现在来看`seek()`的能力：
>>> f.seek(0)
意图是要回到文件的最开头，那么如果用`f.readline()`应该读取第一行。
>>> f.readline()
'You Raise Me Up\n'
果然如此。此时指针所在的位置，还可以用`tell()`来显示，如
>>> f.tell()
17L
这不是在低17行。在Python 2中返回的是`17L`，很容易让人产生如此误解。但是在Python 3中返回的是`17`，又可能迷茫，单位是什么呢？
读者不妨数一数，是按照字符，`'You Raise Me Up\n'`从0开始，到最后，是不是正好为`17`。提醒注意的是，如果你用汉语的等文字，就需要注意编码问题了。请查看本教程有关编码的讨论。
>>> f.seek(4)
`f.seek(4)`就将位置定位到从开头算起的第四个字符后面，也就是"You "之后，字母"R"之前的位置。
>>> f.tell()
4L #Python 3返回：4
`tell()`也是这么说的。这时候如果使用`readline()`，得到就是从当前位置开始到行末。
>>> f.readline()
'Raise Me Up\n'
>>> f.close()
`seek()`还有别的参数，具体如下：
>seek(...)
> seek(offset[, whence]) -> None. Move to new file position.
>
> Argument offset is a byte count. Optional argument whence defaults to
> 0 (offset from start of file, offset should be >= 0); other values are 1
> (move relative to current position, positive or negative), and 2 (move
> relative to end of file, usually negative, although many platforms allow
> seeking beyond the end of a file). If the file is opened in text mode,
> only offsets returned by tell() are legal. Use of other offsets causes
> undefined behavior.
> Note that not all file objects are seekable.
whence的值：
- 默认值是0，表示从文件开头开始计算指针偏移的量（简称偏移量）。这是offset必须是大于等于0的整数。
- 是1时，表示从当前位置开始计算偏移量。offset如果是负数，表示从当前位置向前移动，整数表示向后移动。
- 是2时，表示相对文件末尾移动。
前面已经提到了，文件是可迭代的，并且还学过其它可迭代的对象，看来迭代是一个有必要讨论的问题。
------
[总目录](./index.md) | [上节：文件(1)](./126.md) | [下节：迭代](./128.md)
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