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 = '[ 0-9a-z.\(\)+-\/*=]'

variables = {}

def print_error(error_code):

	# List of error codes:
	# 1 - Invalid characters found in expression
	# 2 - Unclosed parantheses
	# 3 - Two operators next to each other
	# 4 - Wrong number formatting (multiple periods)

	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.")
		case 4:
			print("One of your values is improperly formatted.")
		case 5:
			print("Uninitialized variable.")
	
def check_errors(expr):
	expr_small = expr.replace(" ", "") # Remove spaces from the string, to make it easier to parse

	# Check if number of opening parantheses is equal to number of closing parantheses
	num_open_pars = 0
	num_close_pars = 0
	for index,val in enumerate(expr_small):
		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:
			if expr_small[index + 1] in opers: # Two consecutive operators
				return 3

		if val == '.':
			if not expr_small[index + 1].isdigit():  # If you have a period, you must have a number after it
				return 4


	if num_open_pars != num_close_pars:
		return 2



	expr = parse(expr)
	for val in expr:
		if val.count('.') > 1:  # A value can have at most 1 period
			return 4
		if val.isalpha() and not val in variables and val != expr[0]: # If the token is a string, and isn't in the dictionary, and isn't the variable at index 0 (e.g. 'x' in 'x = 4')
			return 5
	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)

	for index, val in enumerate(subexpr): # Replace variables with their values
		if str(val).isalpha():
			subexpr[index] = variables[val]
	
	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:
		variable = ''
		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_tokenized = parse(expr)

		if expr_tokenized[0].isalpha() and expr_tokenized[1] == '=': # If the expression assigns a value to a variable
			variable = expr_tokenized[0] # The first token is the variable

			expr_tokenized.pop(0) # Remove the first and second tokens
			expr_tokenized.pop(0)

			expr = find_inner(''.join(expr_tokenized))
			variables.update({variable: expr})

		else:
			expr = find_inner(expr)

		print(expr)
		print(variables)

main()