https://www.codewars.com/kata/52a78825cdfc2cfc87000005/fork/python

# Instructions

Given a mathematical expression as a string you must return the result as a number.

## Numbers

Number may be both whole numbers and/or decimal numbers. The same goes for the returned result.

## Operators

You need to support the following mathematical operators:

* Multiplication `*`
* Division `/` (as floating point division)
* Addition `+`
* Subtraction `-`

Operators are always evaluated from left-to-right, and `*` and `/` must be evaluated before `+` and `-`.

## Parentheses

You need to support multiple levels of nested parentheses, ex. `(2 / (2 + 3.33) * 4) - -6`

## Whitespace

There may or may not be whitespace between numbers and operators.

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.

```
1-1    // 0
1 -1   // 0
1- 1   // 0
1 - 1  // 0
1- -1  // 2
1 - -1 // 2
1--1   // 2

6 + -(4)   // 2
6 + -( -4) // 10
```

And the following are **invalid** expressions

```
1 - - 1    // Invalid
1- - 1     // Invalid
6 + - (4)  // Invalid
6 + -(- 4) // Invalid
```

## Validation

You do not need to worry about validation - you will only receive **valid** mathematical expressions following the above rules.

## Restricted APIs

```if:javascript
NOTE: Both `eval` and `Function` are disabled.
```

```if:php
NOTE: `eval` is disallowed in your solution.
```

```if:python
NOTE: `eval` and `exec` are disallowed in your solution.
```
```if:clojure
NOTE: `eval` and `import` are disallowed in your solution.
```

```if:java
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.
```

```if:rust
NOTE: `std::process::Command` is disallowed in your solution.
```