relax strict requirement of future and pyparsing packages

nltk_tgrep/tests/test_tgrep.py

@@ -7,8 +7,12 @@
 (c) 16 March, 2013 Will Roberts
 '''
 
-from __future__ import unicode_literals
-from builtins import range
+from __future__ import print_function, unicode_literals
+try:
+    from builtins import range
+except ImportError:
+    print('Warning: nltk_tgrep may not work correctly on Python 2.* without the ')
+    print('`future` package installed.')
 from nltk.tree import ParentedTree
 from .. import tgrep
 import unittest

nltk_tgrep/tgrep.py

@@ -60,11 +60,19 @@
 macro definitions to `m` and initialises `l` to an empty dictionary.
 '''
 
-from __future__ import unicode_literals
-from builtins import bytes, range, str
+from __future__ import print_function, unicode_literals
+try:
+    from builtins import bytes, range, str
+except ImportError:
+    print('Warning: nltk_tgrep may not work correctly on Python 2.* without the')
+    print('`future` package installed.')
 import functools
 import nltk.tree
-import pyparsing
+try:
+    import pyparsing
+except ImportError:
+    print('Warning: nltk_tgrep will not work without the `pyparsing` package')
+    print('installed.')
 import re
 
 class TgrepException(Exception):