python fileinput中的description

最新推荐文章于 2024-03-04 20:41:00 发布

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最新推荐文章于 2024-03-04 20:41:00 发布

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本文详细介绍了Python中的fileinput模块，包括其基本用法、常见函数介绍及实例演示。讲解了如何利用该模块处理一个或多个文本文件，进行文件读取、行计数等操作。

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fileinput模块提供处理一个或多个文本文件的功能, 可以通过使用for..in来循环读取一个或多个文本文件内容.

例子中的文件，

1.txt
1a

2a
3a
4a

2.txt
1b
2b

DESCRIPTION

Typical use is:

import fileinput

for line in fileinput.input():

process(line)

This iterates over the lines of all files listed in sys.argv[1:],

defaulting to sys.stdin if the list is empty. If a filename is '-' it

is also replaced by sys.stdin. Tospecify an alternative list of

filenames, pass it as the argument to input(). A single file name is

also allowed.

[译]这个迭代了所有文件的行在sys.argv[1:]中，如果列表为空则默认为标准输入，如果文件名为”-”它也为标准输入。指定一个文件名列表来做为参数传递给input，一个单独的文件名也是允许的。

[例]

(1)#!/usr/bin/envpython

importfileinput,sys

for line infileinput.input(sys.argv[1:]):

pass

printfileinput.lineno(),

命令行下，输入python test.py1.txt 2.txt

(2)#!/usr/bin/envpython

import fileinput

for line infileinput.input(['1.txt','2.txt']):

pass

printfileinput.lineno(),

(3) #!/usr/bin/envpython

import fileinput

for line infileinput.input(“1.txt”):

pass

printfileinput.lineno(),

Functions filename(), lineno() return the filename and cumulative line

number of the line that has just been read; filelineno() returns its

line number in the current file; isfirstline() returns true iff the

line just read is the first line of its file; isstdin() returns true

iff the line was read from sys.stdin. Function nextfile() closes the

current file so that the next iteration will read the first line from

the next file (if any); lines not read from the file will not count

towards the cumulative line count; the filename is not changed until

after the first line of the next file has been read. Function close()

closes the sequence.

[译]函数filename,lineno返回的读取的文件名与已经读的累计的行数；filelineno返回当前文件的行数的函数;如果读的是它自己的文件第一行，那么isfirstline是正确的。如果读的是来自标准输入那么isstdin返回真。函数nextfile关闭当前文件以致下一个迭代器将从下一个文件第一行读起；将不会累计上一个文件的行数.这个文件名不会改变，直到读取下一个文件的第一行。函数close关闭序列。

[例]

(1) #!/usr/bin/envpython

import fileinput

for line infileinput.input(['1.txt']):

pass

printfileinput.filename(),fileinput.lineno()

[root@newpatch3/home/python]#python test.py

1.txt 4

(2) #!/usr/bin/env python

import fileinput

for line infileinput.input(['1.txt','2.txt']):

pass

printfileinput.filename(),":",fileinput.filelineno()

print "1.txt and 2.txt totalline:",fileinput.lineno()

[root@newpatch3 /home/python]#pythontest.py

2.txt : 2

1.txt and 2.txt total line: 6

大家看到没，filelineno与lineno的差异了吧？

(3) #!/usr/bin/env python

import fileinput,sys

for line in fileinput.input([‘1.txt’]):

if fileinput.isfirstline():

print line,

sys.exit(0)

[root@newpatch3 /home/python]#pythontest.py

原1.txt中有1a,2a,3a,4a四行数，但我们通过条件判断，只取第一条，来演示isfirstline功能.

(4) #!/usr/bin/env python

import fileinput

for line in fileinput.input():

if fileinput.isstdin():

print "isstdin"

[root@newpatch3 /home/python]#pythontest.py

This is stdin

Isstdin

Before any lines have been read, filename() returns None and both line

numbers are zero; nextfile() has no effect. After all lines have been

read, filename() and the line number functions return the values

pertaining to the last line read; nextfile() has no effect.

[译]没有行读取前，filename返回None和行号为0，nextfile也不起作用。在所有行被读后，filename和获取行号的函数才能返回到已经读的当前行。Nextfile才能起作用。

[例]自己测试。

All files are opened in text mode. If an I/O error occurs during

opening or reading a file, the IOError exception is raised.

[译]所有的文件以文本模式打开，如果在打开或者读一个文件时发生了一个I/O错误，将会产生一个IOError异常。

If sys.stdin is used more than once, the second and further use will

return no lines, except perhaps for interactive use, or if it has been

explicitly reset (e.g. using sys.stdin.seek(0)).

[译]如果标准输入用了多次，第二次将不会返回任何行，除在交互模式下，或者将其重置。

[例]

#!/usr/bin/envpython

import fileinput,sys

for line infileinput.input():

print "line1:",line,

fileinput.close()

sys.stdin.seek(0)

for line infileinput.input():

print "line2:",line,

fileinput.close()

[root@newpatch3/home/python]#python test.py

line1: a

line1: b

line1: c

line2: e

line2: f

line2: g

Empty files are opened and immediately closed; the only time their

presence in the list of filenames is noticeable at all is when the

last file opened is empty.

It is possible that the last line of a file doesn't end in a newline

character; otherwise lines are returned including the trailing

newline.

Class FileInput is the implementation; its methods filename(),

lineno(), fileline(), isfirstline(), isstdin(), nextfile() and close()

correspond to the functions in the module. In addition it has a

readline() method which returns the next input line, and a

__getitem__() method which implements the sequence behavior. The

sequence must be accessed in strictly sequential order; sequence

access and readline() cannot be mixed.

[译]类fileinput是这个的实例；它的方法有filename(),….对应的功能在这个模块中。除此之外还有readline方法，返回下一行输入，和__getitem__()方法。该序列中，必须严格按顺序访问；序例访问和 readline 不能混淆。

Optional in-place filtering: if the keyword argument inplace=1 is

passed to input() or to the FileInput constructor, the file is moved

to a backup file and standard output is directed to the input file.

This makes it possible to write a filter that rewrites its input file

in place. If the keyword argumentbackup=".<some extension>" is also

given, it specifies the extension for the backup file, and the backup

file remains around; by default, the extension is ".bak" andit is

deleted when the output file is closed. In-place filtering is

disabled when standard input is read. XXX The current implementation

does not workfor MS-DOS 8+3 filesystems.

[译]这段话总的意思是说,inplace如果设为1，那么就将读到的行，输出到输入文件中。如果有backup这个参数，就会将源文件内容输入到备份文件中，输出还会输出到输入文件中。

[例]

(1A)#!/usr/bin/envpython

importfileinput,sys

for line infileinput.input("1.txt", inplace=0):

print line,

[root@newpatch3/home/python]#python test.py

[root@newpatch3 /home/python]#more 1.txt

(1B) #!/usr/bin/env python

import fileinput,sys

for line infileinput.input("1.txt",inplace=1):

print “test”,

[root@newpatch3/home/python]#python test.py

[root@newpatch3/home/python]#more 1.txt

test test testtest

通过1A与1B可以发现，我们如果不指定backup的话，就会将输出直接写入到1.txt文件中。

(2) #!/usr/bin/envpython

importfileinput,sys

for line infileinput.input("1.txt",inplace=1,backup=".bak"):

print "test\n",

[root@newpatch3/home/python]#ls

1.txt 1.txt.bak 2.txt test.py

[root@newpatch3/home/python]#more 1.txt

test

[root@newpatch3/home/python]#more 1.txt.bak

Performance: this module is unfortunately one of the slower ways of

processing large numbers of input lines. Nevertheless, a significant

speed-up has been obtained by using readlines(bufsize) instead of

readline(). A new keywordargument, bufsize=N, is present on the

input() function and the FileInput() class to override the default

buffer size.

[译]对与处理大量的输入行的处理是不理想的。然而，一个重要的加速已使用readlines（bufsize）来代替ReadLine（）。一个新的关键参数，bufsize=N,是在input()函数中存在的和FileInput()类中覆盖buffersize的默认值。总的一句话，通过buffersize这个关键函数可以提高大量的输入。