Merge pull request nltk#3303 from strangetom/perf/pos-lru-cache

Use LRU cache when getting POS tagger

Author: stevenbird

AUTHORS.md

@@ -302,6 +302,7 @@
 - Akihiro Yamazaki <https://github.com/zakkie>
 - Ron Urbach <https://github.com/sharpblade4>
 - Vivek Kalyan <https://github.com/vivekkalyan>
+- Tom Strange https://github.com/strangetom
 
 ## Others whose work we've taken and included in NLTK, but who didn't directly contribute it:
 

nltk/tag/__init__.py

@@ -65,6 +65,8 @@
 isort:skip_file
 """
 
+import functools
+
 from nltk.tag.api import TaggerI
 from nltk.tag.util import str2tuple, tuple2str, untag
 from nltk.tag.sequential import (
@@ -100,6 +102,7 @@
 }
 
 
+@functools.lru_cache
 def _get_tagger(lang=None):
     if lang == "rus":
         tagger = PerceptronTagger(lang=lang)