fileinput —- Iterate over lines from multiple input streams

Source code:Lib/fileinput.py

This module implements a helper class and functions to quickly write aloop over standard input or a list of files. If you just want to read orwrite one file see open().

The 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:], defaultingto sys.stdin if the list is empty. If a filename is '-', it is alsoreplaced by sys.stdin and the optional arguments mode and _openhook_are ignored. To specify an alternative list of filenames, pass it as thefirst argument to input(). A single file name is also allowed.

All files are opened in text mode by default, but you can override this byspecifying the mode parameter in the call to input() orFileInput. If an I/O error occurs during opening or reading a file,OSError is raised.

在 3.3 版更改: IOError used to be raised; it is now an alias of OSError.

If sys.stdin is used more than once, the second and further use will returnno lines, except perhaps for interactive use, or if it has been explicitly reset(e.g. using sys.stdin.seek(0)).

Empty files are opened and immediately closed; the only time their presence inthe list of filenames is noticeable at all is when the last file opened isempty.

Lines are returned with any newlines intact, which means that the last line ina file may not have one.

You can control how files are opened by providing an opening hook via theopenhook parameter to fileinput.input() or FileInput(). Thehook must be a function that takes two arguments, filename and mode, andreturns an accordingly opened file-like object. Two useful hooks are alreadyprovided by this module.

The following function is the primary interface of this module:

• fileinput.input(files=None, inplace=False, backup='', *, mode='r', openhook=None)
• Create an instance of the FileInput class. The instance will be usedas global state for the functions of this module, and is also returned to useduring iteration. The parameters to this function will be passed along to theconstructor of the FileInput class.

The FileInput instance can be used as a context manager in thewith statement. In this example, input is closed after thewith statement is exited, even if an exception occurs:

with fileinput.input(files=('spam.txt', 'eggs.txt')) as f:
    for line in f:
        process(line)

在 3.2 版更改: Can be used as a context manager.

在 3.8 版更改: The keyword parameters mode and openhook are now keyword-only.

The following functions use the global state created by fileinput.input();if there is no active state, RuntimeError is raised.

• fileinput.filename()

• Return the name of the file currently being read. Before the first line hasbeen read, returns None.

• fileinput.fileno()

• Return the integer "file descriptor" for the current file. When no file isopened (before the first line and between files), returns -1.

• fileinput.lineno()

• Return the cumulative line number of the line that has just been read. Beforethe first line has been read, returns 0. After the last line of the lastfile has been read, returns the line number of that line.

• fileinput.filelineno()

• Return the line number in the current file. Before the first line has beenread, returns 0. After the last line of the last file has been read,returns the line number of that line within the file.

• fileinput.isfirstline()

• Return True if the line just read is the first line of its file, otherwisereturn False.

• fileinput.isstdin()

• Return True if the last line was read from sys.stdin, otherwise returnFalse.

• fileinput.nextfile()

• Close the current file so that the next iteration will read the first line fromthe next file (if any); lines not read from the file will not count towards thecumulative line count. The filename is not changed until after the first lineof the next file has been read. Before the first line has been read, thisfunction has no effect; it cannot be used to skip the first file. After thelast line of the last file has been read, this function has no effect.

• fileinput.close()

• Close the sequence.

The class which implements the sequence behavior provided by the module isavailable for subclassing as well:

• class fileinput.FileInput(files=None, inplace=False, backup='', *, mode='r', openhook=None)
• Class FileInput is the implementation; its methods filename(),fileno(), lineno(), filelineno(), isfirstline(),isstdin(), nextfile() and close() correspond to thefunctions of the same name in the module. In addition it has areadline() 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; random accessand readline() cannot be mixed.

With mode you can specify which file mode will be passed to open(). Itmust be one of 'r', 'rU', 'U' and 'rb'.

The openhook, when given, must be a function that takes two arguments,filename and mode, and returns an accordingly opened file-like object. Youcannot use inplace and openhook together.

A FileInput instance can be used as a context manager in thewith statement. In this example, input is closed after thewith statement is exited, even if an exception occurs:

with FileInput(files=('spam.txt', 'eggs.txt')) as input:
    process(input)

在 3.2 版更改: Can be used as a context manager.

3.4 版后已移除: The 'rU' and 'U' modes.

3.8 版后已移除: Support for getitem() method is deprecated.

在 3.8 版更改: The keyword parameter mode and openhook are now keyword-only.

Optional in-place filtering: if the keyword argument inplace=True ispassed to fileinput.input() or to the FileInput constructor, thefile is moved to a backup file and standard output is directed to the input file(if a file of the same name as the backup file already exists, it will bereplaced silently). This makes it possible to write a filter that rewrites itsinput file in place. If the backup parameter is given (typically asbackup='.<some extension>'), 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 disabledwhen standard input is read.

The two following opening hooks are provided by this module:

• fileinput.hookcompressed(_filename, mode)
• Transparently opens files compressed with gzip and bzip2 (recognized by theextensions '.gz' and '.bz2') using the gzip and bz2modules. If the filename extension is not '.gz' or '.bz2', the file isopened normally (ie, using open() without any decompression).

Usage example: fi = fileinput.FileInput(openhook=fileinput.hook_compressed)

• fileinput.hookencoded(_encoding, errors=None)
• Returns a hook which opens each file with open(), using the givenencoding and errors to read the file.

Usage example: fi =fileinput.FileInput(openhook=fileinput.hook_encoded("utf-8","surrogateescape"))

在 3.6 版更改: Added the optional errors parameter.