I'm trying to make a constructor without hardcoding all of the values

[Gribouillis]

Here is a working version

#!/usr/bin/env python3
#PublicPizzaClass.py
 
class Pizza:
    #a constructor that initializes 3 attributes for any-topping selfs.
    #right now, the attributes are public, so code outside of this class
    #will be able to get and set the values of these attributes.
    def __init__(self, name, size, price=None, taxPercent=0.05):
        self.name = name
        self.size = size #small = $7, medium = $9, large = $10
        self.taxPercent = taxPercent
        self.price = self.getSizePrice(size) if price is None else price
        
    #a method that associates a size with a price
    @staticmethod
    def getSizePrice(size):
        if size == "Small":
            price = 7.00
        elif size == "Medium":
            price = 9.00
        elif size == "Large":
            price = 10.00
        return price
 
    #a method that uses two attributes to perform a calculation
    def getTaxAmount(self):
        return self.price * self.taxPercent
 
    #a method that calls another method to perform a calculation
    def getTotalPrice(self):
        return self.price + self.getTaxAmount()
    
 
#create two pizza objects
pizza1 = Pizza("Pepperoni", "Large")
pizza2 = Pizza("Sausage", "Medium")
 
print("Name:            {:s}".format(pizza1.name))
print("Price:           {:.2f}".format(pizza1.price))
print("Tax Amount:      {:.2f}".format(pizza1.getTaxAmount()))
print("Total Price:     {:.2f}".format(pizza1.getTotalPrice()))

Note that the implicit first argument in methods is usually named 'self' instead of 'pizza'. In this version, the constructor gives you the opportunity to give a price and tax percent, but if you don't give it, it chooses the default (price from size and tax 0.05).