A more complicated recursive python calculator

calc.py

from collections import OrderedDict

#reverse order of operations
#I didn't have to use an OrderedDict, but it's cute
operations = OrderedDict([
    ("+", lambda x, y: x + y),
    ("-", lambda x, y: x - y),
    ("/", lambda x, y: x / y),
    ("*", lambda x, y: x * y),
    ("^", lambda x, y: x ^ y)
])
    
symbols = operations.keys()

def lex(expr):
    """
    seperates numbers from symbols, recursively nests parens
    """
    tokens = []
    while expr:
        char, *expr = expr
        #char is equal to the first charecter of the expression, expr is equal
        #to the rest of it
        if char == "#":
            #the rest of the line is a comment
            break
        if char == "(":
            try:
                paren, expr = lex(expr)
                tokens.append(paren)
                #expr is what's after the end of the paren, we'll just continue
                #lexing after that''
            except ValueError:
                raise Exception("paren mismatch")
        elif char == ")":
            return tokens, expr
            #returns the tokens leading up to the to the paren and the rest of 
            #the expression after it
        elif char.isdigit() or char == ".":
            #number
            try:
                if tokens[-1] in symbols:
                    tokens.append(char) #start a new num
                elif type(tokens[-1]) is list:
                    raise Exception("parens cannot be followed by numbers")
                    #no support for 5(1+1) yet
                else:
                    tokens[-1] += char #add to last num
            except IndexError:
                #if tokens is empty
                tokens.append(char) #start first num
        elif char in symbols:
            tokens.append(char)
        elif char.isspace():
            pass
        else:
            raise Exception("invalid charecter: " + char)
    return tokens

def evaluate(tokens):
    for symbol, func in operations.items():
        #try to find an operation to eval in order
        try:
            pos = tokens.index(symbol)
            #split the tokens by the operation and eval that
            leftTerm = evaluate(tokens[:pos])
            rightTerm = evaluate(tokens[pos + 1:])
            return func(leftTerm, rightTerm)
            #incidentially, return immediatly breaks all loops within the
            # function
        except ValueError:
            pass
            #index raises ValueError when it's not found
    if len(tokens) is 1:
        try:
            #it must be a number
            return float(tokens[0])
        except TypeError:
            #if it's not a number
            return evaluate(tokens[0])
    else:
        raise Exception("bad expression: " + tokens)

def calc(expr):
    return evaluate(lex(expr))
    
while 1:
    print(calc(input("Input? ")))

gistfile1.txt

$ python3 calc.py
Input? 1 + 1 #simple operations, comments
2.0
Input? 0.1-0.5#floats and negatives, irrelevant whitespace
-0.4
Input? 4 + 4 / 2 - 1 #order of operations is respected
5.0
Input? (4-4 + (3-2) * (((((((7)))))))) # complex parens                                                         
7.0

Uh, sure?

Thank you very much!

Hello!
I was wondering if I have your permission to use your calculator in my project. All credit will go to you, along with a link to your GitHub. The file will be modified slightly to allow math equations similar to 4(8), and of course small spelling differences as well. Is this okay with you?

How did you get the 4(8+8) to work?

Sure! I'm curious what you're using it for

…

On Thu, Jul 16, 2020 at 01:21 nachoregulardude ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ ("^", lambda x, y: x ^ y) this didn't work for me, instead, I used ("^", lambda x, y: pow(x, y)), Great program by the way. Do I have your permission to use this in my calculator? Also for GitHub. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://gist.github.com/5887092#gistcomment-3379139>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAHG4G46OLHFPK6XIZZZJYDR32E5DANCNFSM4IYOMZRA> .

Hello, i have fixed your project. There was a issue with exponential calculation:

Input? 2^2
Traceback (most recent call last):
  File "/home/kuflierl/Software/Test/py/recrusive-calc.py", line 89, in <module>
    print(calc(input("Input? ")))
  File "/home/kuflierl/Software/Test/py/recrusive-calc.py", line 86, in calc
    return evaluate(lex(expr))
  File "/home/kuflierl/Software/Test/py/recrusive-calc.py", line 69, in evaluate
    return func(leftTerm, rightTerm)
  File "/home/kuflierl/Software/Test/py/recrusive-calc.py", line 11, in <lambda>
    ("^", lambda x, y: x ^ y)
TypeError: unsupported operand type(s) for ^: 'float' and 'float'

In python we use ** for exponential calculations. This should fix it:

#!/bin/python3
from collections import OrderedDict

#reverse order of operations
#I didn't have to use an OrderedDict, but it's cute
operations = OrderedDict([
    ("+", lambda x, y: x + y),
    ("-", lambda x, y: x - y),
    ("/", lambda x, y: x / y),
    ("*", lambda x, y: x * y),
    ("^", lambda x, y: x ** y)
])
    
symbols = operations.keys()

def lex(expr):
    """
    seperates numbers from symbols, recursively nests parens
    """
    tokens = []
    while expr:
        char, *expr = expr
        #char is equal to the first charecter of the expression, expr is equal
        #to the rest of it
        if char == "#":
            #the rest of the line is a comment
            break
        if char == "(":
            try:
                paren, expr = lex(expr)
                tokens.append(paren)
                #expr is what's after the end of the paren, we'll just continue
                #lexing after that''
            except ValueError:
                raise Exception("paren mismatch")
        elif char == ")":
            return tokens, expr
            #returns the tokens leading up to the to the paren and the rest of 
            #the expression after it
        elif char.isdigit() or char == ".":
            #number
            try:
                if tokens[-1] in symbols:
                    tokens.append(char) #start a new num
                elif type(tokens[-1]) is list:
                    raise Exception("parens cannot be followed by numbers")
                    #no support for 5(1+1) yet
                else:
                    tokens[-1] += char #add to last num
            except IndexError:
                #if tokens is empty
                tokens.append(char) #start first num
        elif char in symbols:
            tokens.append(char)
        elif char.isspace():
            pass
        else:
            raise Exception("invalid charecter: " + char)
    return tokens

def evaluate(tokens):
    for symbol, func in operations.items():
        #try to find an operation to eval in order
        try:
            pos = tokens.index(symbol)
            #split the tokens by the operation and eval that
            leftTerm = evaluate(tokens[:pos])
            rightTerm = evaluate(tokens[pos + 1:])
            return func(leftTerm, rightTerm)
            #incidentially, return immediatly breaks all loops within the
            # function
        except ValueError:
            pass
            #index raises ValueError when it's not found
    if len(tokens) is 1:
        try:
            #it must be a number
            return float(tokens[0])
        except TypeError:
            #if it's not a number
            return evaluate(tokens[0])
    else:
        raise Exception("bad expression: " + tokens)

while 1:
    print(evaluate(lex(input("Input? "))))

BTW i shortened your project a bit.

thanks for your code very much