✨ Option to set frequency (#145)

* ✨ Option to set frequency - 🔥 Drop Python 3.7 - ⬆️ Update dependencies * Fix annotations
roniemartinez · Jul 6, 2023 · 7a08162 · 7a08162
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diff --git a/.github/dependabot.yml b/.github/dependabot.yml
@@ -5,7 +5,9 @@
 
 version: 2
 updates:
-  - package-ecosystem: "pip" # See documentation for possible values
+
+  # Version updates for Python
+  - package-ecosystem: "pip"
     directory: "/" # Location of package manifests
     schedule:
       interval: "daily"

diff --git a/.github/workflows/python.yml b/.github/workflows/python.yml
@@ -22,7 +22,7 @@ jobs:
     strategy:
       matrix:
         os: [ ubuntu-latest, macos-latest, windows-latest ]
-        python-version: [ '3.7', '3.8', '3.9', '3.10', '3.11' ]
+        python-version: [ '3.8', '3.9', '3.10', '3.11' ]
         include:
           - os: ubuntu-latest
             pip-cache: ~/.cache/pip

diff --git a/README.md b/README.md
@@ -85,13 +85,15 @@ print(
 
 ```bash
 amortize -h
-usage: amortize [-h] -P PRINCIPAL -r INTEREST_RATE [-s] (-n PERIOD | -a AMOUNT)
+usage: amortize [-h] -P PRINCIPAL -r INTEREST_RATE [-s] [-f {daily,biweekly,weekly,semimonthly,monthly,quarterly,semiyearly,yearly}] (-n PERIOD | -a AMOUNT)
 
 Python library for calculating amortizations and generating amortization schedules
 
 options:
   -h, --help            show this help message and exit
   -s, --schedule        Generate amortization schedule
+  -f {daily,biweekly,weekly,semimonthly,monthly,quarterly,semiyearly,yearly}, --frequency {daily,biweekly,weekly,semimonthly,monthly,quarterly,semiyearly,yearly}
+                        Payment frequency
   -n PERIOD, --period PERIOD
                         Total number of periods
   -a AMOUNT, --amount AMOUNT
@@ -101,13 +103,14 @@ required arguments:
   -P PRINCIPAL, --principal PRINCIPAL
                         Principal amount
   -r INTEREST_RATE, --interest-rate INTEREST_RATE
-                        Interest rate per period
+                        Interest rate per year
 ```
 
 ```bash
-amortize -P 150000 -n 36 -r 0.1         # period
-amortize -P 150000 -n 36 -r 0.1 -s      # schedule
-amortize -P 150000 -a 4840.08 -r 0.1    # amount
+amortize -P 150000 -n 36 -r 0.1             # period
+amortize -P 150000 -n 36 -r 0.1 -s          # schedule
+amortize -P 150000 -a 4840.08 -r 0.1        # amount
+amortize -P 150000 -n 36 -r 0.1 -f weekly   # period (specify payment frequency)
 ```
 
 ```bash

diff --git a/amortization/amortize.py b/amortization/amortize.py
@@ -1,6 +1,7 @@
 from typing import Any, List  # pragma: no cover
 
 from amortization.amount import calculate_amortization_amount  # pragma: no cover
+from amortization.enums import PaymentFrequency  # pragma: no cover
 from amortization.period import calculate_amortization_period
 from amortization.schedule import amortization_schedule  # pragma: no cover
 
@@ -10,6 +11,10 @@ def main() -> None:  # pragma: no cover
 
     from tabulate import tabulate
 
+    class ConvertFrequency(argparse.Action):
+        def __call__(self, parser: Any, namespace: Any, values: Any, option_string: Any = None) -> None:
+            setattr(namespace, self.dest, PaymentFrequency[values.upper()])
+
     parser = argparse.ArgumentParser(
         description="Python library for calculating amortizations and generating amortization schedules"
     )
@@ -29,7 +34,7 @@ def main() -> None:  # pragma: no cover
         dest="interest_rate",
         type=float,
         required=True,
-        help="Interest rate per period",
+        help="Interest rate per year",
     )
     # optional parameters
     parser.add_argument(
@@ -40,6 +45,16 @@ def main() -> None:  # pragma: no cover
         action="store_true",
         help="Generate amortization schedule",
     )
+    parser.add_argument(
+        "-f",
+        "--frequency",
+        dest="frequency",
+        default=PaymentFrequency.MONTHLY,
+        type=str,
+        action=ConvertFrequency,
+        choices=("daily", "biweekly", "weekly", "semimonthly", "monthly", "quarterly", "semiyearly", "yearly"),
+        help="Payment frequency",
+    )
     mutually_exclusive = parser.add_mutually_exclusive_group(required=True)
     mutually_exclusive.add_argument(
         "-n",
@@ -61,7 +76,9 @@ def main() -> None:  # pragma: no cover
             parser.error("-s/--schedule requires -n/--period")
         total_paid = total_interest = total_principal = 0.0
         table: List[Any] = []
-        for row in amortization_schedule(arguments.principal, arguments.interest_rate, arguments.period):
+        for row in amortization_schedule(
+            arguments.principal, arguments.interest_rate, arguments.period, arguments.frequency
+        ):
             table.append(row)
             total_paid += row[1]
             total_interest += row[2]
@@ -76,8 +93,12 @@ def main() -> None:  # pragma: no cover
             )
         )
     elif arguments.amount:
-        period = calculate_amortization_period(arguments.principal, arguments.interest_rate, arguments.amount)
+        period = calculate_amortization_period(
+            arguments.principal, arguments.interest_rate, arguments.amount, arguments.frequency
+        )
         print("Amortization period: {}".format(period))
     else:
-        amount = calculate_amortization_amount(arguments.principal, arguments.interest_rate, arguments.period)
+        amount = calculate_amortization_amount(
+            arguments.principal, arguments.interest_rate, arguments.period, arguments.frequency
+        )
         print("Amortization amount: {:,.2f}".format(amount))
diff --git a/amortization/amount.py b/amortization/amount.py
@@ -1,15 +1,24 @@
-def calculate_amortization_amount(principal: float, interest_rate: float, period: int) -> float:
+from amortization.enums import PaymentFrequency
+
+
+def calculate_amortization_amount(
+    principal: float, interest_rate: float, period: int, payment_frequency: PaymentFrequency = PaymentFrequency.MONTHLY
+) -> float:
     """
     Calculates Amortization Amount per period
 
     >>> calculate_amortization_amount(150000, 0.1, 36)
     4840.08
 
+    >>> calculate_amortization_amount(150000, 0.1, 36, PaymentFrequency.SEMIMONTHLY)
+    4495.63
+
     :param principal: Principal amount
-    :param interest_rate: Interest rate per period
+    :param interest_rate: Interest rate per year
     :param period: Total number of period
+    :param payment_frequency: Payment frequency per year
     :return: Amortization amount per period
     """
-    adjusted_interest = interest_rate / 12
+    adjusted_interest = interest_rate / payment_frequency.value
     x = (1 + adjusted_interest) ** period
     return round(principal * (adjusted_interest * x) / (x - 1), 2)
diff --git a/amortization/enums.py b/amortization/enums.py
@@ -0,0 +1,12 @@
+from enum import Enum
+
+
+class PaymentFrequency(Enum):
+    DAILY = 365
+    BIWEEKLY = 104
+    WEEKLY = 52
+    SEMIMONTHLY = 24
+    MONTHLY = 12
+    QUARTERLY = 4
+    SEMIYEARLY = 2
+    YEARLY = 1
diff --git a/amortization/period.py b/amortization/period.py
@@ -1,17 +1,28 @@
 from math import log
 
+from amortization.enums import PaymentFrequency
 
-def calculate_amortization_period(principal: float, interest_rate: float, amount: float) -> int:
+
+def calculate_amortization_period(
+    principal: float,
+    interest_rate: float,
+    amount: float,
+    payment_frequency: PaymentFrequency = PaymentFrequency.MONTHLY,
+) -> int:
     """
     Calculates the number of period needed for a given amortization amount
 
     >>> calculate_amortization_period(150000, 0.1, 4840.08)
     36
 
+    >>> calculate_amortization_period(150000, 0.1, 4500, PaymentFrequency.WEEKLY)
+    34
+
     :param principal: Principal amount
-    :param interest_rate: Interest rate per period
+    :param interest_rate: Interest rate per year
     :param amount: Amortization amount per period
+    :param payment_frequency: Payment frequency per year
     :return: Total number of period
     """
-    adjusted_interest = interest_rate / 12
+    adjusted_interest = interest_rate / payment_frequency.value
     return round(log(amount / (amount - adjusted_interest * principal), 1 + adjusted_interest))
diff --git a/amortization/schedule.py b/amortization/schedule.py
@@ -1,21 +1,23 @@
 from typing import Iterator, Tuple
 
 from amortization.amount import calculate_amortization_amount
+from amortization.enums import PaymentFrequency
 
 
 def amortization_schedule(
-    principal: float, interest_rate: float, period: int
+    principal: float, interest_rate: float, period: int, payment_frequency: PaymentFrequency = PaymentFrequency.MONTHLY
 ) -> Iterator[Tuple[int, float, float, float, float]]:
     """
     Generates amortization schedule
 
     :param principal: Principal amount
-    :param interest_rate: Interest rate per period
+    :param interest_rate: Interest rate per year
     :param period: Total number of periods
+    :param payment_frequency: Payment frequency per year
     :return: Rows containing period, amount, interest, principal, balance, etc
     """
-    amortization_amount = calculate_amortization_amount(principal, interest_rate, period)
-    adjusted_interest = interest_rate / 12
+    amortization_amount = calculate_amortization_amount(principal, interest_rate, period, payment_frequency)
+    adjusted_interest = interest_rate / payment_frequency.value
     balance = principal
     for number in range(1, period + 1):
         interest = round(balance * adjusted_interest, 2)