date parsing replaced with _parse_date function

This is to avoid ambiguity and keep date parsing uniform

fincal/fincal.py

@@ -5,7 +5,7 @@ from typing import List, Union
 
 from dateutil.relativedelta import relativedelta
 
-from .core import AllFrequencies, TimeSeriesCore, _preprocess_match_options
+from .core import AllFrequencies, TimeSeriesCore, _parse_date, _preprocess_match_options
 
 
 def create_date_series(
@@ -113,12 +113,13 @@ class TimeSeries(TimeSeriesCore):
 
     def calculate_returns(
         self,
-        as_on: datetime.datetime,
+        as_on: Union[str, datetime.datetime],
         as_on_match: str = "closest",
         prior_match: str = "closest",
         closest: str = "previous",
         compounding: bool = True,
         years: int = 1,
+        date_format: str = None
     ) -> float:
         """Method to calculate returns for a certain time-period as on a particular date
 
@@ -158,6 +159,7 @@ class TimeSeries(TimeSeriesCore):
         >>> calculate_returns(datetime.date(2020, 1, 1), years=1)
         """
 
+        as_on = _parse_date(as_on, date_format)
         as_on_delta, prior_delta = _preprocess_match_options(as_on_match, prior_match, closest)
 
         while True:
@@ -184,21 +186,28 @@ class TimeSeries(TimeSeriesCore):
 
     def calculate_rolling_returns(
         self,
-        from_date: datetime.date,
+        from_date: Union[datetime.date, str],
-        to_date: datetime.date,
+        to_date: Union[datetime.date, str],
-        frequency: str = "D",
+        frequency: str = None,
         as_on_match: str = "closest",
         prior_match: str = "closest",
         closest: str = "previous",
         compounding: bool = True,
         years: int = 1,
+        date_format: str = None
     ) -> List[tuple]:
         """Calculates the rolling return"""
 
-        try:
+        from_date = _parse_date(from_date, date_format)
-            frequency = getattr(AllFrequencies, frequency)
+        to_date = _parse_date(to_date, date_format)
-        except AttributeError:
+
-            raise ValueError(f"Invalid argument for frequency {frequency}")
+        if frequency is None:
+            frequency = self.frequency
+        else:
+            try:
+                frequency = getattr(AllFrequencies, frequency)
+            except AttributeError:
+                raise ValueError(f"Invalid argument for frequency {frequency}")
 
         dates = create_date_series(from_date, to_date, frequency.symbol)
         if frequency == AllFrequencies.D: