bpo-33338: [tokenize] Minor code cleanup (python#6573)

This change contains minor things that make diffing between Lib/tokenize.py and
Lib/lib2to3/pgen2/tokenize.py cleaner.

Lib/tokenize.py

@@ -28,7 +28,6 @@
 from codecs import lookup, BOM_UTF8
 import collections
 from io import TextIOWrapper
-from itertools import chain
 import itertools as _itertools
 import re
 import sys
@@ -278,7 +277,7 @@ def compat(self, token, iterable):
         startline = token[0] in (NEWLINE, NL)
         prevstring = False
 
-        for tok in chain([token], iterable):
+        for tok in _itertools.chain([token], iterable):
             toknum, tokval = tok[:2]
             if toknum == ENCODING:
                 self.encoding = tokval
@@ -475,13 +474,10 @@ def tokenize(readline):
     The first token sequence will always be an ENCODING token
     which tells you which encoding was used to decode the bytes stream.
     """
-    # This import is here to avoid problems when the itertools module is not
-    # built yet and tokenize is imported.
-    from itertools import chain, repeat
     encoding, consumed = detect_encoding(readline)
-    rl_gen = iter(readline, b"")
-    empty = repeat(b"")
-    return _tokenize(chain(consumed, rl_gen, empty).__next__, encoding)
+    empty = _itertools.repeat(b"")
+    rl_gen = _itertools.chain(consumed, iter(readline, b""), empty)
+    return _tokenize(rl_gen.__next__, encoding)
 
 
 def _tokenize(readline, encoding):
@@ -496,7 +492,7 @@ def _tokenize(readline, encoding):
             # BOM will already have been stripped.
             encoding = "utf-8"
         yield TokenInfo(ENCODING, encoding, (0, 0), (0, 0), '')
-    while True:             # loop over lines in stream
+    while True:                                # loop over lines in stream
         try:
             line = readline()
         except StopIteration:
@@ -581,7 +577,7 @@ def _tokenize(readline, encoding):
                     continue
                 token, initial = line[start:end], line[start]
 
-                if (initial in numchars or                  # ordinary number
+                if (initial in numchars or                 # ordinary number
                     (initial == '.' and token != '.' and token != '...')):
                     yield TokenInfo(NUMBER, token, spos, epos, line)
                 elif initial in '\r\n':
@@ -667,7 +663,8 @@ def main():
 
     # Helper error handling routines
     def perror(message):
-        print(message, file=sys.stderr)
+        sys.stderr.write(message)
+        sys.stderr.write('\n')
 
     def error(message, filename=None, location=None):
         if location: