Deprecate the 'U' open mode

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
@@ skipping 206 matching lines @@
         self._filelineno = 0
         self._file = None
         self._isstdin = False
         self._backupfilename = None
         self._buffer = []
         self._bufindex = 0
         # restrict mode argument to reading modes
         if mode not in ('r', 'rU', 'U', 'rb'):
             raise ValueError("FileInput opening mode must be one of "
                              "'r', 'rU', 'U' and 'rb'")
+        if 'U' in mode:
+            warnings.warn("Use of 'U' mode is deprecated",
+                          DeprecationWarning)
         self._mode = mode
         if openhook:
             if inplace:
                 raise ValueError("FileInput cannot use an opening hook in inplace mode")
             if not callable(openhook):
                 raise ValueError("FileInput openhook must be callable")
         self._openhook = openhook
 
     def __del__(self):
         self.close()
@@ skipping 176 matching lines @@
         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()