Merge remote-tracking branch 'upstream/develop' into develop

Author: ekaf

AUTHORS.md

@@ -201,6 +201,7 @@
 - Álvaro Justen <https://github.com/turicas>
 - bjut-hz
 - Sergio Oller
+- Izam Mohammed <https://github.com/izam-mohammed>
 - Will Monroe
 - Elijah Rippeth
 - Emil Manukyan

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 Hi! Thanks for your interest in contributing to [NLTK](https://www.nltk.org/).
 :-) You'll be joining a [long list of contributors](https://github.com/nltk/nltk/blob/develop/AUTHORS.md).
-In this document we'll try to summarize everything that you need to know to
+In this document, we'll try to summarize everything that you need to know to
 do a good job.
 
 
@@ -36,7 +36,7 @@ Some priority areas for development are listed in the [NLTK Wiki](https://github
 We use [Git](https://git-scm.com/) as our [version control
 system](https://en.wikipedia.org/wiki/Revision_control), so the best way to
 contribute is to learn how to use it and put your changes on a Git repository.
-There's a plenty of documentation about Git -- you can start with the [Pro Git
+There's plenty of documentation about Git -- you can start with the [Pro Git
 book](https://git-scm.com/book/).
 
 
@@ -99,7 +99,7 @@ Summary of our git branching model:
 - If you have push access to the main repository, please do not commit directly
   to `develop`: your access should be used only to accept pull requests; if you
   want to make a new feature, you should use the same process as other
-  developers so you code will be reviewed.
+  developers so your code will be reviewed.
 - See [RELEASE-HOWTO.txt](RELEASE-HOWTO.txt) to see everything you
   need before creating a new NLTK release.
 

nltk/grammar.py

@@ -69,6 +69,7 @@
 "expanding" *lhs* to *rhs* in *tree*.
 """
 import re
+from collections import deque
 from functools import total_ordering
 
 from nltk.featstruct import SLASH, TYPE, FeatDict, FeatStruct, FeatStructReader
@@ -771,15 +772,15 @@ def remove_unitary_rules(cls, grammar):
         lexical
         """
         result = []
-        unitary = []
+        unitary = deque([])
         for rule in grammar.productions():
             if len(rule) == 1 and rule.is_nonlexical():
                 unitary.append(rule)
             else:
                 result.append(rule)
 
         while unitary:
-            rule = unitary.pop(0)
+            rule = unitary.popleft()
             for item in grammar.productions(lhs=rule.rhs()[0]):
                 new_rule = Production(rule.lhs(), item.rhs())
                 if len(new_rule) != 1 or new_rule.is_lexical():