python标准库介绍——15 fileinput 模块详解

``fileinput`` 模块允许你循环一个或多个文本文件的内容, 如 [Example 2-1 #eg-2-1] 所示.

====Example 2-1. 使用 fileinput 模块循环一个文本文件====[eg-2-1]

```
File: fileinput-example-1.py

import fileinput
import sys

for line in fileinput.input("samples/sample.txt"):
    sys.stdout.write("-> ")
    sys.stdout.write(line)

*B*-> We will perhaps eventually be writing only small
-> modules which are identified by name as they are
-> used to build larger ones, so that devices like
-> indentation, rather than delimiters, might become
-> feasible for expressing local structure in the
-> source language.
->      -- Donald E. Knuth, December 1974*b*
```

你也可以使用 ``fileinput`` 模块获得当前行的元信息 (meta information). 其中包括 ``isfirstline`` , 
``filename`` , ``lineno`` , 如 [Example 2-2 #eg-2-2] 所示.

====Example 2-2. 使用 fileinput 模块处理多个文本文件====[eg-2-2]

```
File: fileinput-example-2.py

import fileinput
import glob
import string, sys

for line in fileinput.input(glob.glob("samples/*.txt")):
    if fileinput.isfirstline(): # first in a file?
        sys.stderr.write("-- reading %s --\n" % fileinput.filename())
    sys.stdout.write(str(fileinput.lineno()) + " " + string.upper(line))

*B*-- reading samples\sample.txt --
1 WE WILL PERHAPS EVENTUALLY BE WRITING ONLY SMALL
2 MODULES WHICH ARE IDENTIFIED BY NAME AS THEY ARE
3 USED TO BUILD LARGER ONES, SO THAT DEVICES LIKE
4 INDENTATION, RATHER THAN DELIMITERS, MIGHT BECOME
5 FEASIBLE FOR EXPRESSING LOCAL STRUCTURE IN THE
6 SOURCE LANGUAGE.
7    -- DONALD E. KNUTH, DECEMBER 1974*b*
```

文本文件的替换操作很简单. 只需要把 ``inplace`` 关键字参数设置为 1 , 
传递给 ``input`` 函数, 该模块会帮你做好一切. [Example 2-3 #eg-2-3] 展示了这些.

====Example 2-3. 使用 fileinput 模块将 CRLF 改为 LF====[eg-2-3]

```
File: fileinput-example-3.py

import fileinput, sys

for line in fileinput.input(inplace=1):
    # convert Windows/DOS text files to Unix files
    if line[-2:] == "\r\n":
        line = line[:-2] + "\n"
    sys.stdout.write(line)
```