A new standard module, as discussed on comp.lang.python, to simplify

the writing of filters.

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 or when a filename is
'-'.

There is also an option to use this to direct the output back to the
input files.

Lib/fileinput.py

+"""Helper class to quickly write a loop over all standard input files.
+
+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.  To specify an alternative list of
+filenames, pass it as the argument to input().  A single file name is
+also allowed.
+
+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.
+
+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.
+
+All files are opened in text mode.  If an I/O error occurs during
+opening or reading a file, the IOError exception is raised.
+
+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)).
+
+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.
+
+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 argument backup=".<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" and it is
+deleted when the output file is closed.  In-place filtering is
+disabled when standard input is read.  XXX The current implementation
+does not work for MS-DOS 8+3 filesystems.
+
+XXX Possible additions:
+
+- optional getopt argument processing
+- specify open mode ('r' or 'rb')
+- specify buffer size
+- fileno()
+- isatty()
+- read(), read(size), even readlines()
+
+"""
+
+import sys, os
+
+_state = None
+
+def input(files=(), inplace=0, backup=""):
+    global _state
+    if _state and _state._file:
+	raise RuntimeError, "input() already active"
+    _state = FileInput(files, inplace, backup)
+    return _state
+
+def close():
+    global _state
+    state = _state
+    _state = None
+    if state:
+	state.close()
+
+def nextfile():
+    if not _state:
+	raise RuntimeError, "no active input()"
+    return _state.nextfile()
+
+def filename():
+    if not _state:
+	raise RuntimeError, "no active input()"
+    return _state.filename()
+
+def lineno():
+    if not _state:
+	raise RuntimeError, "no active input()"
+    return _state.lineno()
+
+def filelineno():
+    if not _state:
+	raise RuntimeError, "no active input()"
+    return _state.filelineno()
+
+def isfirstline():
+    if not _state:
+	raise RuntimeError, "no active input()"
+    return _state.isfirstline()
+
+def isstdin():
+    if not _state:
+	raise RuntimeError, "no active input()"
+    return _state.isstdin()
+
+class FileInput:
+
+    def __init__(self, files=(), inplace=0, backup=""):
+	if type(files) == type(''):
+	    files = (files,)
+	else:
+	    files = tuple(files)
+	    if not files:
+		files = tuple(sys.argv[1:])
+		if not files:
+		    files = ('-',)
+	self._files = files
+	self._inplace = inplace
+	self._backup = backup
+	self._savestdout = None
+	self._output = None
+	self._filename = None
+	self._lineno = 0
+	self._filelineno = 0
+	self._file = None
+	self._isstdin = 0
+
+    def __del__(self):
+	self.close()
+
+    def close(self):
+	self.nextfile()
+	self._files = ()
+
+    def __getitem__(self, i):
+	if i != self._lineno:
+	    raise RuntimeError, "accessing lines out of order"
+	line = self.readline()
+	if not line:
+	    raise IndexError, "end of input reached"
+	return line
+
+    def nextfile(self):
+	savestdout = self._savestdout
+	self._savestdout = 0
+	if savestdout:
+	    sys.stdout = savestdout
+
+	output = self._output
+	self._output = 0
+	if output:
+	    output.close()
+
+	file = self._file
+	self._file = 0
+	if file and not self._isstdin:
+	    file.close()
+
+	backupfilename = self._backupfilename
+	self._backupfilename = 0
+	if backupfilename and not self._backup:
+	    try: os.unlink(backupfilename)
+	    except: pass
+
+	self._isstdin = 0
+
+    def readline(self):
+	if not self._file:
+	    if not self._files:
+		return ""
+	    self._filename = self._files[0]
+	    self._files = self._files[1:]
+	    self._filelineno = 0
+	    self._file = None
+	    self._isstdin = 0
+	    self._backupfilename = 0
+	    if self._filename == '-':
+		self._filename = '<stdin>'
+		self._file = sys.stdin
+		self._isstdin = 1
+	    else:
+		if self._inplace:
+		    self._backupfilename = (
+			self._filename + (self._backup or ".bak"))
+		    try: os.unlink(self._backupfilename)
+		    except os.error: pass
+		    # The next three lines may raise IOError
+		    os.rename(self._filename, self._backupfilename)
+		    self._file = open(self._backupfilename, "r")
+		    self._output = open(self._filename, "w")
+		    self._savestdout = sys.stdout
+		    sys.stdout = self._output
+		else:
+		    # This may raise IOError
+		    self._file = open(self._filename, "r")
+	line = self._file.readline()
+	if line:
+	    self._lineno = self._lineno + 1
+	    self._filelineno = self._filelineno + 1
+	    return line
+	self.nextfile()
+	# Recursive call
+	return self.readline()
+
+    def filename(self):
+	return self._filename
+
+    def lineno(self):
+	return self._lineno
+
+    def filelineno(self):
+	return self._filelineno
+
+    def isfirstline(self):
+	return self._filelineno == 1
+
+    def isstdin(self):
+	return self._isstdin
+
+def _test():
+    import getopt
+    inplace = 0
+    backup = 0
+    opts, args = getopt.getopt(sys.argv[1:], "ib:")
+    for o, a in opts:
+	if o == '-i': inplace = 1
+	if o == '-b': backup = a
+    for line in input(args, inplace=inplace, backup=backup):
+	if line[-1:] == '\n': line = line[:-1]
+	if line[-1:] == '\r': line = line[:-1]
+	print "%d: %s[%d]%s %s" % (lineno(), filename(), filelineno(),
+				   isfirstline() and "*" or "", line)
+    print "%d: %s[%d]" % (lineno(), filename(), filelineno())
+
+if __name__ == '__main__':
+    _test()