feat: create straight_line_depreciation

Author: Jeonghyun Min

financial/straight_line_depreciation.py

@@ -0,0 +1,103 @@
+"""
+In accounting, depreciation refers to the decreases in the value
+of a fixed asset during the asset's useful life.
+When an organization purchases a fixed asset,
+the purchase expenditure is not recognized as an expense immediately.
+Instead, the decreases in the asset's value are recognized as expenses
+over the years during which the asset is used.
+
+The following methods are widely used
+for depreciation calculation in accounting:
+- Straight-line method
+- Diminishing balance method
+- Units-of-production method
+
+The straight-line method is the simplest and most widely used.
+This method calculates depreciation by spreading the cost evenly
+over the asset's useful life.
+
+The following formula shows how to calculate the yearly depreciation expense:
+
+- annual depreciation expense =
+    (purchase cost of asset - residual value) / useful life of asset(years)
+
+Further information on:
+https://en.wikipedia.org/wiki/Depreciation
+
+The function, straight_line_depreciation, returns a list of
+the depreciation expenses over the given period.
+"""
+
+
+def straight_line_depreciation(
+    useful_years: int,
+    purchase_value: float,
+    residual_value: float = 0.0,
+) -> list[float]:
+    """
+    Calculate the depreciation expenses over the given period
+    :param useful_years: Number of years the asset will be used
+    :param purchase_value: Purchase expenditure for the asset
+    :param residual_value: Residual value of the asset at the end of its useful life
+    :return: A list of annual depreciation expenses over the asset's useful life
+    >>> straight_line_depreciation(10, 1100.0, 100.0)
+    [100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0]
+    >>> straight_line_depreciation(6, 1250.0, 50.0)
+    [200.0, 200.0, 200.0, 200.0, 200.0, 200.0]
+    >>> straight_line_depreciation(4, 1001.0)
+    [250.25, 250.25, 250.25, 250.25]
+    >>> straight_line_depreciation(11, 380.0, 50.0)
+    [30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0]
+    >>> straight_line_depreciation(1, 4985, 100)
+    [4885.0]
+    """
+
+    if not isinstance(useful_years, int):
+        raise TypeError("Useful years must be an integer")
+
+    if useful_years < 1:
+        raise ValueError("Useful years cannot be less than 1")
+
+    if not isinstance(purchase_value, (float, int)):
+        raise TypeError("Purchase value must be numeric")
+
+    if not isinstance(residual_value, (float, int)):
+        raise TypeError("Residual value must be numeric")
+
+    if purchase_value < 0.0:
+        raise ValueError("Purchase value cannot be less than zero")
+
+    if purchase_value < residual_value:
+        raise ValueError("Purchase value cannot be less than residual value")
+
+    # Calculate annual depreciation expense
+    depreciable_cost = purchase_value - residual_value
+    annual_depreciation_expense = depreciable_cost / useful_years
+
+    # List of annual depreciation expenses
+    list_of_depreciation_expenses = []
+    accumulated_depreciation_expense = 0.0
+    for period in range(useful_years):
+        if period != useful_years - 1:
+            accumulated_depreciation_expense += annual_depreciation_expense
+            list_of_depreciation_expenses.append(annual_depreciation_expense)
+        else:
+            depreciation_expense_in_end_year = (
+                depreciable_cost - accumulated_depreciation_expense
+            )
+            list_of_depreciation_expenses.append(depreciation_expense_in_end_year)
+
+    return list_of_depreciation_expenses
+
+
+if __name__ == "__main__":
+    user_input_useful_years = int(input("Please Enter Useful Years:\n > "))
+    user_input_purchase_value = float(input("Please Enter Purchase Value:\n > "))
+    user_input_residual_value = float(input("Please Enter Residual Value:\n > "))
+    print(
+        straight_line_depreciation(
+            user_input_useful_years,
+            user_input_purchase_value,
+            user_input_residual_value,
+        )
+    )