Splitting a math expression string into tokens in Python

Question

I have a lot of python strings such as \"A7*4\", \"Z3+8\", \"B6 / 11\", and I want to split these strings so that they would be in a l

Answer 1

You should split on the character set [+-/*] after removing the whitespace from the string:

>>> import re
>>> def mysplit(mystr):
...     return re.split("([+-/*])", mystr.replace(" ", ""))
...
>>> mysplit("A7*4")
['A7', '*', '4']
>>> mysplit("Z3+8")
['Z3', '+', '8']
>>> mysplit("B6 / 11")
['B6', '/', '11']
>>>

Answer 2

There is a way to solve this without regular expressions by using the Python tokenizer. I used a more complex formula to show the capabilities of this solution.

from io import StringIO
import tokenize

formula = "(A7*4) - (Z3+8) -  ( B6 / 11)"
print([token[1] for token in tokenize.generate_tokens(StringIO(formula).readline) if token[1]])

Result:

['(', 'A7', '*', '4', ')', '-', '(', 'Z3', '+', '8', ')', '-', '(', 'B6', '/', '11', ')']