Custom Class
Case Study: Building Software in Python
Mark Pedigo
Principal Data Scientist
Roadmap
Monthly Mortgage Calculation
The formula for the monthly mortgage calculation is
$$\text{monthly payment} = P \cdot \frac{r (1 + r)^N}{(1+r)^N - 1},$$
where
- $P$ is the loan amount,
- $r$ is the monthly interest rate, and
- $N$ is the number of monthly payments
1 https://en.wikipedia.org/wiki/Mortgage_calculator
Add Functionality to Our Class
Method to calculate the monthly payment
def monthly_payment(self):
# Compute the multiplier
numerator = self.monthly_interest_rate * \
(1 + self.monthly_interest_rate) ** self.months
denominator = (1 + self.monthly_interest_rate) ** self.months - 1
multiplier = self.divide(numerator, denominator)
# Calculate the monthly payment
monthly_payment = self.multiply(self.loan_amount, multiplier)
return monthly_payment
Compute the Monthly Payment
# Instantiate a mortgage calculator
mortgage_calculator = calculators.MortgageCalculator(300000, 0.065, 30)
# Calculate the monthly payment
print(round(mortgage_calculator.monthly_payment, 2))
1703.37
dir() again
dir(ClassName)- list of the functions of a class
dir(MortgageCalculator)
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__',
'__format__', '__ge__', '__getattribute__', '__getstate__', '__gt__', '__hash__',
'__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__',
'__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__',
'__str__', '__subclasshook__', '__weakref__',
'calculate_monthly_payment', 'difference', 'monthly_interest',
'monthly_interest_rate', 'monthly_payment', 'months', 'power', 'principal',
'product', 'quotient', 'sum']
F-string Example
name = "Alice"
age = 17
# Using an f-string to include variables in a sentence
greeting = f"Hello, my name is {name} and I'm {age} years old."
print(greeting)
Hello, my name is Alice and I'm 17 years old.
Let's practice!
Case Study: Building Software in Python
