pycalc/calculator.py

import re
from parse import *

# List of valid operators
opers = ['+', '-', '*', '/']

# Regular expression that checks for valid characters in an expression
valid_chars = '[ 0-9.\(\)+-\/*]'

def print_error(error_code):

	# List of error codes:
	# 1 - Invalid characters found in expression
	# 2 - Unclosed parantheses

	match error_code:
		case 1:
			print("You have invalid characters in your expression.")
		case 2:
			print("You have an unclosed parantheses in your expression.")
		case 3:
			print("You have two operators next to each other.")
	
def check_errors(expr):
	# Check if number of opening parantheses is equal to number of closing parantheses
	num_open_pars = 0
	num_close_pars = 0
	for val in expr:
		if not re.match(valid_chars, val):
			return 1

		num_open_pars = num_open_pars+1 if val == '(' else num_open_pars 
		num_close_pars = num_close_pars+1 if val == ')' else num_close_pars

		if val in opers:
			#Check if the next element is an operator. If it is, throw an error
			continue

	if num_open_pars != num_close_pars:
		return 2


	return 0
		

def evaluate(subexpr): # Evaluate a tokenized expression, that contains no parantheses

	subexpr = [element for element in subexpr if element != ''] # Remove empty characters in the expression

	print(subexpr)

	if (len(subexpr) == 1):
		return float(subexpr[0])

	if '/' in subexpr:
		index = subexpr.index('/')
		subexpr[index] = float(subexpr[index-1]) / float(subexpr[index+1])
		subexpr[index-1] = ''
		subexpr[index+1] = ''
	elif '*' in subexpr:
		index = subexpr.index('*')
		subexpr[index] = float(subexpr[index-1]) * float(subexpr[index+1])
		subexpr[index-1] = ''
		subexpr[index+1] = ''
	elif '+' in subexpr:
		index = subexpr.index('+')
		subexpr[index] = float(subexpr[index-1]) + float(subexpr[index+1])
		subexpr[index-1] = ''
		subexpr[index+1] = ''
	elif '-' in subexpr:
		index = subexpr.index('-')
		subexpr[index] = float(subexpr[index-1]) - float(subexpr[index+1])
		subexpr[index-1] = ''
		subexpr[index+1] = ''
			
	print(subexpr)

	return evaluate(subexpr)

def find_inner(subexpr):
	print("expr: "  + subexpr)

	subexpr = parse(subexpr)

	for index,val in enumerate(subexpr):
		if '(' in val or ')' in val:
			subexpr[index] = find_inner(val[1:len(val)-1])


	subexpr_string = ''.join(subexpr)
	print("New expr: " + subexpr_string)
	if not '(' in subexpr_string and not ')' in subexpr_string:
		return str(evaluate(subexpr))

	

def main():
	while True:
		expr = input()
		errno = check_errors(expr)
		if errno != 0:
			print_error(errno)
			continue # If an error was generated, print an error message and continue on to the next iteration of the loop
		expr = find_inner(expr)
		print(expr)

main()