python models: Add Date.strptime constructor.

python/status_report.py

@@ -4,6 +4,7 @@ import argparse
 import collections
 import csv
 import datetime
+import functools
 import os
 import sys
 
@@ -15,14 +16,12 @@ from supporters.models import Date, Payment, Supporter
 
 MONTH_FMT = '%Y-%m'
 
-def month_date(arg_s):
-    return Date.from_pydate(datetime.datetime.strptime(arg_s, MONTH_FMT))
-
 def parse_arguments(arglist):
     parser = argparse.ArgumentParser(
         prog='status_report',
         description="Print a CSV report counting Supporters over time",
     )
+    month_date = functools.partial(Date.strptime, fmt=MONTH_FMT)
     parser.add_argument(
         '--start-month', type=month_date, metavar='YYYY-MM',
         default=Payment.objects.order_by('date').first().date,

python/supporters/models.py

@@ -2,6 +2,7 @@
 
 import datetime
 import operator
+import time
 
 from django.db import models
 
@@ -25,6 +26,11 @@ class Date(datetime.date):
     def from_pydate(cls, date):
         return cls(date.year, date.month, date.day)
 
+    @classmethod
+    def strptime(cls, s, fmt):
+        time_tuple = time.strptime(s, fmt)
+        return cls(*time_tuple[:3])
+
     def adjust_month(self, delta, day=None):
         if day is None:
             day = self.day