Add time.first_of_year() convenience function

rattail/time.py

@@ -183,6 +183,13 @@ def last_of_month(date):
     return date.replace(day=last_day)
 
 
+def first_of_year(date):
+    """
+    Returns a date representing the first day of whichever year ``date`` falls in.
+    """
+    return date.replace(month=1, day=1)
+
+
 def date_range(start, end, step=1):
     """
     Generator which yields all dates between ``start`` and ``end``, *inclusive*.