An interpreter for math expressions.
Example:
In [3]: e = Expression('10-4+5')
In [4]: e.evaluate()
Out[4]: 11.0
In [2]: e = Expression('10/2')
In [3]: e.evaluate()
Out[3]: 5.0
Note:
- Math operators do not have priority yet.
- Parenthesis are not being interpreted yet.
- Operations with negative numbers (e.g. -1+2) do not work well.