Evaluate mathematical expression
https://www.codewars.com/kata/52a78825cdfc2cfc87000005/solutions/python
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https://www.codewars.com/kata/52a78825cdfc2cfc87000005/fork/python
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# Instructions
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Given a mathematical expression as a string you must return the result as a number.
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## Numbers
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Number may be both whole numbers and/or decimal numbers. The same goes for the returned result.
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## Operators
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You need to support the following mathematical operators:
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* Multiplication `*`
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* Division `/` (as floating point division)
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* Addition `+`
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* Subtraction `-`
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Operators are always evaluated from left-to-right, and `*` and `/` must be evaluated before `+` and `-`.
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## Parentheses
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You need to support multiple levels of nested parentheses, ex. `(2 / (2 + 3.33) * 4) - -6`
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## Whitespace
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There may or may not be whitespace between numbers and operators.
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An addition to this rule is that the minus sign (`-`) used for negating numbers and parentheses will *never* be separated by whitespace. I.e all of the following are **valid** expressions.
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```
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1-1 // 0
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1 -1 // 0
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1- 1 // 0
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1 - 1 // 0
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1- -1 // 2
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1 - -1 // 2
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1--1 // 2
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6 + -(4) // 2
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6 + -( -4) // 10
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```
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And the following are **invalid** expressions
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```
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1 - - 1 // Invalid
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1- - 1 // Invalid
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6 + - (4) // Invalid
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6 + -(- 4) // Invalid
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```
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## Validation
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You do not need to worry about validation - you will only receive **valid** mathematical expressions following the above rules.
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## Restricted APIs
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```if:javascript
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NOTE: Both `eval` and `Function` are disabled.
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```
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```if:php
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NOTE: `eval` is disallowed in your solution.
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```
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```if:python
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NOTE: `eval` and `exec` are disallowed in your solution.
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```
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```if:clojure
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NOTE: `eval` and `import` are disallowed in your solution.
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```
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```if:java
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NOTE: To keep up the difficulty of the kata, use of some classes and functions is disallowed. Their names cannot appear in the solution file, even in comments and variable names.
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```
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```if:rust
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NOTE: `std::process::Command` is disallowed in your solution.
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```
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import re
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from enum import Enum
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from dataclasses import dataclass
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class TokenType(Enum):
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INTEGER = 1
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FLOATING = 2
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PLUS = 3,
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MINUS = 4,
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MULT = 5,
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DIV = 6,
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OPEN_PAREN = 7,
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CLOSE_PAREN = 8
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@dataclass
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class Token:
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type: TokenType
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value: str | int
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def tokenize(expr):
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scanner = re.Scanner((
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(r"\d+", lambda scanner,token: Token(TokenType.INTEGER, token)),
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(r"\d+\.\d", lambda scanner,token: Token(TokenType.FLOATING, token)),
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(r"\+", lambda scanner,token: Token(TokenType.PLUS, token)),
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(r"\-", lambda scanner,token: Token(TokenType.MINUS, token)),
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(r"\*", lambda scanner,token: Token(TokenType.MULT, token)),
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(r"\/", lambda scanner,token: Token(TokenType.DIV, token)),
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(r"\(", lambda scanner,token: Token(TokenType.OPEN_PAREN, token)),
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(r"\)", lambda scanner,token: Token(TokenType.CLOSE_PAREN, token)),
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(r"\s+", None)
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))
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tokens, unknown = scanner.scan(expr)
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assert len(unknown) == 0, f"Unknown token: {unknown}"
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return tokens
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class Parser:
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def __init__(self, tokens):
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self.tokens = tokens
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self.pos = 0
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def _accept(self, token_type) -> Token | None:
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if self.pos < len(self.tokens) and self.tokens[self.pos].type == token_type:
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token = self.tokens[self.pos]
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self.pos += 1
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return token
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return None
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def parse_expr(self):
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tree = self.parse_expr_plus()
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assert self.pos == len(self.tokens), "Not all tokens where consumed!"
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return tree
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def parse_expr_plus(self):
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lhs = self.parse_expr_mult()
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while ((token := self._accept(TokenType.PLUS)) is not None
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or (token := self._accept(TokenType.MINUS)) is not None):
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rhs = self.parse_expr_mult()
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if token.type == TokenType.PLUS:
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lhs += rhs
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elif token.type == TokenType.MINUS:
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lhs -= rhs
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else:
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raise SyntaxError(f"Unexpected token {token[0]}")
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return lhs
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def parse_expr_mult(self):
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lhs = self.parse_primary()
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while ((token := self._accept(TokenType.MULT)) is not None
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or (token := self._accept(TokenType.DIV)) is not None):
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if token.type == TokenType.MULT:
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lhs *= self.parse_primary()
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elif token.type == TokenType.DIV:
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lhs /= self.parse_primary()
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else:
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raise SyntaxError(f"Unexpected token {token[0]}")
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return lhs
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def parse_primary(self):
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assert self.pos <= len(self.tokens)
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sign = 1
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if self._accept(TokenType.MINUS) is not None:
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sign *= -1
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if (token := self._accept(TokenType.INTEGER)) is not None:
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return sign * int(token.value)
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elif (token := self._accept(TokenType.OPEN_PAREN)) is not None:
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expr = self.parse_expr_plus()
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if self._accept(TokenType.CLOSE_PAREN) is None:
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raise SyntaxError(f"Expected token {TokenType.CLOSE_PAREN}")
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return sign * expr
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assert False, f"Unexpected token type for parse_primary: {self.tokens[self.pos][0]}"
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def calc(expression):
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p = Parser(tokenize(expression))
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try:
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return p.parse_expr()
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except:
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print(expression)
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print(p.tokens)
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raise
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from solution import calc
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import codewars_test as test
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import random
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@test.describe("Fixed tests")
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def _():
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@test.it("Tests")
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def __():
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cases = (
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("1 + 1", 2),
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("8/16", 0.5),
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("3 -(-1)", 4),
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("2 + -2", 0),
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("10- 2- -5", 13),
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("(((10)))", 10),
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("3 * 5", 15),
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("-7 * -(6 / 3)", 14)
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)
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for x, y in cases:
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test.assert_equals(calc(x), y)
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@test.describe("Random tests")
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def _():
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choice = random.choice
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randint = random.randint
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@test.it("Tests")
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def __():
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for i in range(100):
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try:
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s = "{}{} {} {}{} {} {}{} {} {}{} {} {}{} {} {}{} {} {}{} {} {}{}".format(choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100))
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test.assert_approx_equals(calc(s), eval(s), 1e-6, s)
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except ZeroDivisionError:
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test.pass_()
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for i in range(100):
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try:
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s = "{}({}{}) {} ({}{} {} {}{} {} {}({})) {} ({}{} {} {}((({}({}{} {} {}{})))) {} {}{})".format(choice(["-", ""]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), choice(["-", ""]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100), choice(["+", "-", "*", "/"]), choice(["-", ""]), randint(1, 100))
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test.assert_approx_equals(calc(s), eval(s), 1e-6, s)
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except ZeroDivisionError:
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test.pass_()
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for i in range(100):
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s = "{}{}- {}{}- {}{}- {}{}".format(choice(["-", ""]), randint(1, 100), choice(["-", ""]), randint(1, 100), choice(["-", ""]), randint(1, 100), choice(["-", ""]), randint(1, 100))
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test.assert_approx_equals(calc(s), eval(s), 1e-6, s)
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