improves the exception details
@@ -561,7 +561,7 @@ class Period(object):
date = datetime.strptime(string, date_format)
except ValueError:
# Parsing failed.
- raise InvalidQueryArgumentTypeError(string, datetime)
+ raise InvalidQueryArgumentTypeError(string, 'a valid datetime string')
precision = cls.precisions[ordinal]
return cls(date, precision)
