User input validation & docstring update

projects/Loan Calculator/main.py

@@ -1,29 +1,95 @@
+TOTAL_PERCENT = 100
+MONTH = 12
+
+
 def calculate_loan_payment(principal, annual_interest_rate, months):
-    # Convert annual interest rate to monthly rate
-    monthly_interest_rate = annual_interest_rate / 12 / 100
+    """
+    Convert annual interest rate to monthly rate
+    Args:
+        principal(float): The principal amount for the loan
+        annual_interest_rate(float): The interest rate for the amount annually.
+        months(int): The timeframe for the loan repayment in months.
+
+    Returns:
+    monthly_payment(float): The amount of money that needs to be paid monthly.
+    """
+
+    monthly_interest_rate = annual_interest_rate / MONTH / 100
 
     # Calculate monthly payment
     if monthly_interest_rate == 0:
         monthly_payment = principal / months
     else:
         monthly_payment = (
-            principal
-            * (monthly_interest_rate * (1 + monthly_interest_rate) ** months)
-            / ((1 + monthly_interest_rate) ** months - 1)
+                principal
+                * (monthly_interest_rate * (1 + monthly_interest_rate) ** months)
+                / ((1 + monthly_interest_rate) ** months - 1)
         )
 
     return monthly_payment
 
 
+def get_months():
+    """
+    This function gets the loan repayment in months.
+    Returns:
+    months(int): The timeframe for the loan repayment in months.
+    Error Message: Displays an error message if the user inputs are invalid.
+    """
+    while True:
+        try:
+            months = int(input("Enter the loan term (in months): "))
+            if months < 0:
+                print("Enter a valid interest rate in percentage")
+            else:
+                return months
+        except ValueError:
+            print("Enter a valid numeric value for loan term in months")
+
+
+def get_interest_rate():
+    """
+    This function gets the interest rate for a year.
+    Returns:
+    annual_interest_rate(float): The interest rate for the amount annually.
+    Error Message: Displays an error message if the user inputs are invalid.
+    """
+    while True:
+        try:
+            annual_interest_rate = float(input("Enter the annual interest rate (as a percentage): "))
+            if annual_interest_rate < 0 or annual_interest_rate > TOTAL_PERCENT:
+                print("Enter a valid interest rate in percentage")
+            else:
+                return annual_interest_rate
+        except ValueError:
+            print("Enter a valid numeric percentage for interest rate")
+
+
+def get_principal():
+    """
+    This function fetches the principal amount for the loan
+    Returns:
+    principal(float): The principal amount for the loan.
+    Error Message: Displays an error message if the user inputs are invalid.
+    """
+    while True:
+        try:
+            principal = float(input("Enter the loan amount: $"))
+            if principal <= 0:
+                print("Enter a valid amount for the principal")
+            else:
+                return principal
+        except ValueError:
+            print("Invalid Input. Please enter a numeric value for the principal.")
+
+
 def main():
     print("Welcome to the Loan Calculator!")
 
     # Get user input
-    principal = float(input("Enter the loan amount: $"))
-    annual_interest_rate = float(
-        input("Enter the annual interest rate (as a percentage): ")
-    )
-    months = int(input("Enter the loan term (in months): "))
+    principal = get_principal()
+    annual_interest_rate = get_interest_rate()
+    months = get_months()
 
     # Calculate monthly payment
     monthly_payment = calculate_loan_payment(principal, annual_interest_rate, months)

projects/Loan Calculator/test_loancalculator.py

@@ -0,0 +1,22 @@
+import unittest
+from main import calculate_loan_payment, get_months
+
+
+def test_calculate_loan_payment():
+    # Define the expected monthly payment
+    expected_payment = 167.75198511394362
+
+    # Define the input parameters for the function
+    principal = 2000
+    annual_interest_rate = 1.2
+    months = 12
+
+    # Calculate the monthly payment using the function you want to test
+    monthly_payment = calculate_loan_payment(principal, annual_interest_rate, months)
+
+    # Use the assert statement to check if the calculated payment matches the expected payment
+    assert monthly_payment == expected_payment
+
+
+if __name__ == '__main__':
+    test_calculate_loan_payment()