improved getitem, head, and tail functions

fincal/core.py

@@ -3,7 +3,7 @@ import inspect
 from collections import UserDict, UserList
 from dataclasses import dataclass
 from numbers import Number
-from typing import Iterable, List, Literal, Sequence, Tuple
+from typing import Iterable, List, Literal, Mapping, Sequence, Union
 
 from .utils import _parse_date, _preprocess_timeseries
 
@@ -32,7 +32,7 @@ def date_parser(*pos):
     ...         return diff.days
     ...     return diff
     ...
-    >>> calculate_difference(date1='2019-01-01'm date2='2020-01-01')
+    >>> calculate_difference(date1='2019-01-01', date2='2020-01-01')
     datetime.timedelta(365)
 
     Each of the dates is automatically parsed into a datetime.datetime object from string.
@@ -83,7 +83,7 @@ class AllFrequencies:
 class _IndexSlicer:
     """Class to create a slice using iloc in TimeSeriesCore"""
 
-    def __init__(self, parent_obj):
+    def __init__(self, parent_obj: object):
         self.parent = parent_obj
 
     def __getitem__(self, n):
@@ -95,7 +95,7 @@ class _IndexSlicer:
         if len(item) == 1:
             return item[0]
 
-        return item
+        return self.parent.__class__(item, self.parent.frequency.symbol)
 
 
 class Series(UserList):
@@ -319,38 +319,46 @@ class TimeSeriesCore(UserDict):
             printable_str = "[{}]".format(",\n ".join([str(i) for i in self.data.items()]))
         return printable_str
 
-    def __getitem__(self, key):
-        if isinstance(key, Series):
-            if not key.dtype == bool:
-                raise ValueError(f"Cannot slice {self.__class__.__name__} using a Series of {key.dtype.__name__}")
-            elif len(key) != len(self.dates):
-                raise Exception(f"Length of Series: {len(key)} did not match length of object: {len(self.dates)}")
-            else:
-                dates = self.dates
-                dates_to_return = [dates[i] for i, j in enumerate(key) if j]
-                data_to_return = [(key, self.data[key]) for key in dates_to_return]
-                return self.__class__(data_to_return, frequency=self.frequency.symbol)
+    @date_parser(1)
+    def _get_item_from_date(self, date: Union[str, datetime.datetime]):
+        return date, self.data[date]
 
+    def _get_item_from_key(self, key: Union[str, datetime.datetime]):
         if isinstance(key, int):
-            raise KeyError(f"{key}. For index based slicing, use .iloc[{key}]")
-        elif isinstance(key, (datetime.datetime, datetime.date)):
-            key = _parse_date(key)
-            item = (key, self.data[key])
-        elif isinstance(key, str):
-            if key == "dates":
-                return self.dates
-            elif key == "values":
-                return self.values
-
-            dt_key = _parse_date(key)
-            item = (dt_key, self.data[dt_key])
-
-        elif isinstance(key, Sequence):
-            keys = [_parse_date(i) for i in key]
-            item = [(k, self.data[k]) for k in keys]
+            raise KeyError(f"{key}. \nHint: use .iloc[{key}] for index based slicing.")
+
+        if key in ["dates", "values"]:
+            return getattr(self, key)
+
+        return self._get_item_from_date(key)
+
+    def _get_item_from_list(self, date_list: Sequence[Union[str, datetime.datetime]]):
+        data_to_return = [self._get_item_from_key(key) for key in date_list]
+        return self.__class__(data_to_return, frequency=self.frequency.symbol)
+
+    def _get_item_from_series(self, series: Series):
+        if series.dtype == bool:
+            if len(series) != len(self.dates):
+                raise ValueError(f"Length of Series: {len(series)} did not match length of object: {len(self.dates)}")
+            dates_to_return = [self.dates[i] for i, j in enumerate(series) if j]
+        elif series.dtype == datetime.datetime:
+            dates_to_return = list(series)
         else:
-            raise TypeError(f"Invalid type {repr(type(key).__name__)} for slicing.")
-        return item
+            raise TypeError(f"Cannot slice {self.__class__.__name__} using a Series of {series.dtype.__name__}")
+
+        return self._get_item_from_list(dates_to_return)
+
+    def __getitem__(self, key):
+        if isinstance(key, (int, str, datetime.datetime, datetime.date)):
+            return self._get_item_from_key(key)
+
+        if isinstance(key, Series):
+            return self._get_item_from_series(key)
+
+        if isinstance(key, Sequence):
+            return self._get_item_from_list(key)
+
+        raise TypeError(f"Invalid type {repr(type(key).__name__)} for slicing.")
 
     def __iter__(self):
         self.n = 0
@@ -364,31 +372,12 @@ class TimeSeriesCore(UserDict):
             self.n += 1
             return key, self.data[key]
 
+    @date_parser(1)
     def __contains__(self, key: object) -> bool:
-        key = _parse_date(key)
         return super().__contains__(key)
 
-    def head(self, n: int = 6):
-        """Returns the first n items of the TimeSeries object"""
-
-        keys = list(self.data.keys())
-        keys = keys[:n]
-        result = [(key, self.data[key]) for key in keys]
-        return result
-
-    def tail(self, n: int = 6):
-        """Returns the last n items of the TimeSeries object"""
-
-        keys = list(self.data.keys())
-        keys = keys[-n:]
-        result = [(key, self.data[key]) for key in keys]
-        return result
-
-    def items(self):
-        return self.data.items()
-
     @property
-    def iloc(self) -> List[Tuple[datetime.datetime, float]]:
+    def iloc(self) -> Mapping:
         """Returns an item or a set of items based on index
 
             supports slicing using numerical index.
@@ -406,3 +395,16 @@ class TimeSeriesCore(UserDict):
         """
 
         return _IndexSlicer(self)
+
+    def head(self, n: int = 6):
+        """Returns the first n items of the TimeSeries object"""
+
+        return self.iloc[:n]
+
+    def tail(self, n: int = 6):
+        """Returns the last n items of the TimeSeries object"""
+
+        return self.iloc[-n:]
+
+    def items(self):
+        return self.data.items()