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 seeopen().

The typical use is:

importfileinputforlineinfileinput.input(encoding="utf-8"):process(line)

This iterates over the lines of all files listed insys.argv[1:], defaultingtosys.stdin if the list is empty. If a filename is'-', it is alsoreplaced bysys.stdin and the optional argumentsmode andopenhookare ignored. To specify an alternative list of filenames, pass it as thefirst argument toinput(). A single file name is also allowed.

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

Ifsys.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. usingsys.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 tofileinput.input() orFileInput(). Thehook must be a function that takes two arguments,filename andmode, andreturns an accordingly opened file-like object. Ifencoding and/orerrorsare specified, they will be passed to the hook as additional keyword arguments.This module provides ahook_compressed() to support compressed files.

The following function is the primary interface of this module:

fileinput.input(files=None,inplace=False,backup='',*,mode='r',openhook=None,encoding=None,errors=None)¶

Create an instance of theFileInput 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 theFileInput class.

TheFileInput 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:

withfileinput.input(files=('spam.txt','eggs.txt'),encoding="utf-8")asf:forlineinf:process(line)

Changed in version 3.2:Can be used as a context manager.

Changed in version 3.8:The keyword parametersmode andopenhook are now keyword-only.

Changed in version 3.10:The keyword-only parameterencoding anderrors are added.

The following functions use the global state created byfileinput.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, returnsNone.

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, returns0. 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, returns0. After the last line of the last file has been read,returns the line number of that line within the file.

fileinput.isfirstline()¶

ReturnTrue if the line just read is the first line of its file, otherwisereturnFalse.

fileinput.isstdin()¶

ReturnTrue if the last line was read fromsys.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:

classfileinput.FileInput(files=None,inplace=False,backup='',*,mode='r',openhook=None,encoding=None,errors=None)¶

ClassFileInput is the implementation; its methodsfilename(),fileno(),lineno(),filelineno(),isfirstline(),isstdin(),nextfile() andclose() correspond to thefunctions of the same name in the module. In addition it isiterableand has areadline() method which returns the nextinput line. The sequence must be accessed in strictly sequential order;random access andreadline() cannot be mixed.

Withmode you can specify which file mode will be passed toopen(). Itmust be one of'r' and'rb'.

Theopenhook, when given, must be a function that takes two arguments,filename andmode, and returns an accordingly opened file-like object. Youcannot useinplace andopenhook together.

You can specifyencoding anderrors that is passed toopen() oropenhook.

AFileInput 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:

withFileInput(files=('spam.txt','eggs.txt'))asinput:process(input)

Changed in version 3.2:Can be used as a context manager.

Changed in version 3.8:The keyword parametermode andopenhook are now keyword-only.

Changed in version 3.10:The keyword-only parameterencoding anderrors are added.

Changed in version 3.11:The'rU' and'U' modes and the__getitem__() method havebeen removed.

Optional in-place filtering: if the keyword argumentinplace=True ispassed tofileinput.input() or to theFileInput 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 thebackup parameter is given (typically asbackup='.<someextension>'), 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.hook_compressed(filename,mode,*,encoding=None,errors=None)¶

Transparently opens files compressed with gzip and bzip2 (recognized by theextensions'.gz' and'.bz2') using thegzip andbz2modules. If the filename extension is not'.gz' or'.bz2', the file isopened normally (ie, usingopen() without any decompression).

Theencoding anderrors values are passed toio.TextIOWrapperfor compressed files and open for normal files.

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

Changed in version 3.10:The keyword-only parameterencoding anderrors are added.

fileinput.hook_encoded(encoding,errors=None)¶

Returns a hook which opens each file withopen(), using the givenencoding anderrors to read the file.

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

Changed in version 3.6:Added the optionalerrors parameter.

Deprecated since version 3.10:This function is deprecated sincefileinput.input() andFileInputnow haveencoding anderrors parameters.