Add the parse function

setup.py

@@ -3,7 +3,7 @@
 
 setup(
     name='django-variable-resolution-date',
-    version='0.1.6',
+    version='0.1.7',
     description='A django field that can represent either a year, or a year and a month, or a full calendar date',
     long_description='',
     author='Nicholas Wolff',

tests/test_field.py

@@ -18,14 +18,14 @@ def test_it_can_create_vrd_with_full_date(self):
     def test_it_cannot_create_vrd_with_invalid_full_date(self):
         with raises(ValidationError) as ex:
             ClubMember(name='dave', member_since='1997-02-29').full_clean()
-        assert ex.value.messages == ['Enter a year, year-month, or year-month-day.']
+        assert ex.value.messages == ['Must be a valid year, year-month, or year-month-day.']
 
     def test_it_cannot_create_vrd_with_extra_characters(self):
         with raises(ValidationError) as ex:
             ClubMember(name='earl', member_since='20001').full_clean()
-        assert ex.value.messages == ['Enter a year, year-month, or year-month-day.']
+        assert ex.value.messages == ['Must be a valid year, year-month, or year-month-day.']
 
     def test_it_cannot_create_vrd_with_month_day(self):
         with raises(ValidationError) as ex:
             ClubMember(name='fred', member_since='02-03').full_clean()
-        assert ex.value.messages == ['Enter a year, year-month, or year-month-day.']
+        assert ex.value.messages == ['Must be a valid year, year-month, or year-month-day.']

tests/test_parsing.py

@@ -0,0 +1,40 @@
+from django.core.exceptions import ValidationError
+from django.test import TestCase
+from pytest import raises
+
+from variable_resolution_date import parse
+
+
+class VariableResolutionDateFieldTest(TestCase):
+    def test_it_can_parse_vrd_with_year(self):
+        y, m, d = parse('1996')
+        assert y == 1996
+        assert m is None
+        assert d is None
+
+    def test_it_can_parse_vrd_with_year_and_month(self):
+        y, m, d = parse('1996-02')
+        assert y == 1996
+        assert m == 2
+        assert d is None
+
+    def test_it_can_parse_vrd_with_full_date(self):
+        y, m, d = parse('1996-02-29')
+        assert y == 1996
+        assert m == 2
+        assert d is 29
+
+    def test_it_cannot_parse_vrd_with_invalid_full_date(self):
+        with raises(ValidationError) as ex:
+            parse('1997-02-29')
+        assert ex.value.messages == ['Must be a valid year, year-month, or year-month-day.']
+
+    def test_it_cannot_parse_vrd_with_extra_characters(self):
+        with raises(ValidationError) as ex:
+            parse('20001')
+        assert ex.value.messages == ['Must be a valid year, year-month, or year-month-day.']
+
+    def test_it_cannot_parse_vrd_with_month_day(self):
+        with raises(ValidationError) as ex:
+            parse('02-03')
+        assert ex.value.messages == ['Must be a valid year, year-month, or year-month-day.']

variable_resolution_date/__init__.py

@@ -23,22 +23,28 @@
 VARIABLE_RESOLUTION_DATE_LENGTH = 10
 
 
-def validate_variable_resolution_date(value):
+def parse(value):
+    """ returns a triple: year, month, day (month and day may be None) """
     match = VARIABLE_RESOLUTION_DATE_RE.match(force_text(value))
     if match:
         year = int(match.group(1))
-        month = int(match.group(2) or 1)
-        day = int(match.group(3) or 1)
+        month = int(match.group(2)) if match.group(2) else None
+        day = int(match.group(3)) if match.group(3) else None
         try:
-            datetime.date(year, month, day)
-            return
-        except Exception:
+            # Make sure the different parts taken together represent a valid date.
+            datetime.date(year, month or 1, day or 1)
+            return year, month, day
+        except ValueError:
             pass
-    raise ValidationError('Enter a year, year-month, or year-month-day.')
+    raise ValidationError('Must be a valid year, year-month, or year-month-day.')
+
+
+def validate(value):
+    parse(value)
 
 
 class VariableResolutionDateField(models.CharField):
-    default_validators = [validate_variable_resolution_date]
+    default_validators = [validate]
     description = 'A year, year-month, or year-month-day date'
 
     def __init__(self, *args, **kwargs):