I am creating a very simple Calculator class and I want to create a subtraction method that works self sufficiently, or at least within the methods specified by the class itself.
The problem is that, for subtraction if I use the -= similarly to how I use the += for the addition, it will not work properly and give me the first number already subtracted to the starting value of 0.
The method takes in *args, so I can give as many numbers as I want, and I am now trying to make it so that it takes the first argument/number as default value and then subtracts the sum (using my own addition method) of the other numbers to this number.
This is the code I came up with until now:
class Calculator:
"""An attempt to create a calculator."""
def __init__(self):
self.current_value = 0
# type hinting stuff:
# https://stackoverflow.com/questions/50928592/mypy-type-hint-unionfloat-int-is-there-a-number-type
def add(self, *args: float, reset=False):
"""
Takes in a series of numbers as iterable and sums them up.
If the iterable is empty, or has only one value, the function is invalid.
:param args: Creates an iterable of any number. Can be `int` or `float`.
:param reset: A boolean flag. If set to True, resets the current value to 0.
:return: Return the sum of the 'start' value (default: 0) plus an iterable of numbers.
"""
if reset:
self.current_value = 0
if len(args) >= 1:
total = self.current_value
for num in args:
if isinstance(num, (int, float)):
total += num
else:
print(f"Insert only valid numbers (integers or floats). Try again...")
self.current_value = total
return total
else:
print(f"Insert at least one valid number (integer or float). Try again...")
def subtract(self, *args: float, reset=True):
"""
Takes in a series of numbers as iterable and subtracts them to the starting value of the first number.
If the iterable is empty, the function returns 0.
:param args: Creates an iterable of any number. Can be `int` or `float`.
:param reset: A boolean flag. If set to True, resets the current value to 0.
:return: Return the subtraction of the values inputted as iterables.
"""
if reset:
self.current_value = 0
if len(args) >= 1:
for num in args:
if isinstance(num, (int, float)):
arg += num
continue
else:
print(f"Insert only valid numbers (floats or integers). Try again...")
return None
print(f'Current value: {self.current_value}')
print(f'Sum of args', self.add(args))
total = self.current_value - self.add(args)
self.current_value = total
return total
else:
print(f"Insert at least one valid number (integer or float). Try again...")
The current value is used to retain memory of the previous operations. So, for example if I do add(5,2) = 7 and then call subtract(3) it will be = 4 because the calculator has 7 stored in its memory until I reset it manually.
Subtracting numbers is the same as adding the negative of each number. So you could simplify subtract() to:
def subtract(self, *args: float, reset=True):
return self.add(*(-arg for arg in args), reset=reset)