def get_digits(self):
"""
This pushes numbers in stack. Then it converts that stack into a dictionary value with an alphabetic key.
The reason we do this is that the calculations function cannot handle multiple digits because it is
processing each element by character. For example, 2 + 2 can be processed but 10 + 10 cannot because it would
be expecting a + - * / operator between the 1 and the 0.
It is easier to have proxy variables, such as A + B rather than 10 + 10, and use that to pull dictionary values.
The result would look like self.numbers.get('A') + self.numbers.get('B') with the self.numbers dictionary
looking like {'A': 10, 'B': 10}. The calculator would read this as 10 + 10 without issue.
Thus, the purpose of this function is to build that self.numbers dictionary and build self.final_infix with
alphabetical variables substituting multi-digit numbers. self.final_infix is a word that looks like 'A+B'.
"""
operands = Stack()
alphabet_num = 65
for char in self.infix_split:
if char in '0123456789.':
operands.push(char)
elif not operands.isempty():
alphabet = chr(alphabet_num)
alphabet_num += 1
number = ''
# Converts number into a dictionary item.
while not operands.isempty():
number = operands.pop() + number
self.numbers[alphabet] = number
self.final_infix += alphabet + char
else:
self.final_infix += char
def calculations(self):
"""
This is where the calculator does its magic.
To see how this function works, please reference the textbook material on Chapter 3 Stacks. This algorithm was
built by making an algorithm that takes an infix expression and transforms it into a postfix expression
(2+2 --> 22+). Then, by taking that postfix expression and processing the operators and operands it until there
is only 1 element in the stack, we get the postfix answer, which is the same answer for the infix expression.
(22+ --> 4)
It is possible to build a calculator with simply those 2 algorithms linked up to each other. However, this
function is a hybrid of the two where it is able to simultaneously work with operators and operands, such that
when an infix expression is determined to be in postfix expression, we immediately calculate the answer.
"""
precedent = {'*': 3, '/': 3, '+': 2, '-': 2, '(': 1}
operator_stack = Stack()
operand_stack = Stack()
for item in self.final_infix:
if item in string.ascii_letters:
operand_stack.push(self.numbers.get(item))
elif item == '(':
operator_stack.push(item)
elif item == ')':
# Here be dragons.
top_of_stack = operator_stack.pop()
while top_of_stack != '(':
operand2 = float(operand_stack.pop())
operand1 = float(operand_stack.pop())
operand_stack.push(self.do_math(top_of_stack, operand1, operand2))
top_of_stack = operator_stack.pop()
elif item in precedent:
while (not operator_stack.isempty()) and precedent[operator_stack.peek()] >= precedent[item]:
operand2 = float(operand_stack.pop())
operand1 = float(operand_stack.pop())
operand_stack.push(self.do_math(operator_stack.pop(), operand1, operand2))
operator_stack.push(item)
elif item == '~':
# This is a helper variable to signal the end of infix expression and empty all stacks.
while not operator_stack.isempty():
operand2 = float(operand_stack.pop())
operand1 = float(operand_stack.pop())
operand_stack.push(self.do_math(operator_stack.pop(), operand1, operand2))
else:
raise TypeError('Error: Calculations blew up.')
self.answer = operand_stack.pop()
