Defer generating case-insensitive lookups

Addresses lp:1835784 performance issue

2 files changed, 8 insertions, 1 deletions

diff --git a/gen_tzinfo.py b/gen_tzinfo.py
index d06fa0e..5c0066c 100644
--- a/gen_tzinfo.py
+++ b/gen_tzinfo.py
@@ -129,7 +129,8 @@ def add_allzones(filename):
         tz for tz in all_timezones if resource_exists(tz))
         '''
     print >> outf, 'all_timezones_set = LazySet(all_timezones)'
-    print >> outf, '_all_timezones_lower_to_standard = dict((tz.lower(), tz) for tz in all_timezones)'
+    # Per lp:1835784 we can't afford to do this at import time
+    # print >> outf, '_all_timezones_lower_to_standard = dict((tz.lower(), tz) for tz in all_timezones)'
 
     print >> outf, 'common_timezones = \\'
     pprint(cz, outf)
diff --git a/src/pytz/__init__.py b/src/pytz/__init__.py
index 5c05066..4d8f21d 100644
--- a/src/pytz/__init__.py
+++ b/src/pytz/__init__.py
@@ -188,8 +188,14 @@ def _unmunge_zone(zone):
     return zone.replace('_plus_', '+').replace('_minus_', '-')
 
 
+_all_timezones_lower_to_standard = None
+
+
 def _case_insensitive_zone_lookup(zone):
     """case-insensitively matching timezone, else return zone unchanged"""
+    global _all_timezones_lower_to_standard
+    if _all_timezones_lower_to_standard is None:
+        _all_timezones_lower_to_standard = dict((tz.lower(), tz) for tz in all_timezones)  # noqa
     return _all_timezones_lower_to_standard.get(zone.lower()) or zone  # noqa