Avoid issues with LC_NUMERIC locale (#436)

* Avoid issues with LC_NUMERIC locale

* Use C locale instead of en_US as that may not be installed on all systems

---------

Co-authored-by: Patrick Peglar <[email protected]>

cf_units/__init__.py

@@ -14,7 +14,9 @@
 """
 
 import copy
+import locale
 import math
+import threading
 from contextlib import contextmanager
 from warnings import warn
 
@@ -175,11 +177,25 @@ def suppress_errors():
         _ud.set_error_message_handler(_default_handler)
 
 
+LOCALE_LOCK = threading.Lock()
+
+
+@contextmanager
+def c_locale():
+    with LOCALE_LOCK:
+        lc_numeric = locale.getlocale(locale.LC_NUMERIC)
+        locale.setlocale(locale.LC_NUMERIC, "C")
+        try:
+            yield
+        finally:
+            locale.setlocale(locale.LC_NUMERIC, lc_numeric)
+
+
 #
 # load the UDUNITS-2 xml-formatted unit-database
 #:
 # Ignore standard noisy UDUNITS-2 start-up.
-with suppress_errors():
+with suppress_errors(), c_locale():
     # Load the unit-database from the default location (modified via
     # the UDUNITS2_XML_PATH environment variable) and if that fails look
     # relative to sys.prefix to support environments such as conda.