How to correct the error?

[metulburr]

a non regex method using string methods....

>>> z = '346 + 324 - 368'
>>> x = z.maketrans('+-','..')
>>> x
{43: 46, 45: 46}
>>> y = z.translate(x).split('.')
>>> y
['346 ', ' 324 ', ' 368']

of course at this point its a list and each string is not separate by one single space

>>> a = list(map(str.strip, y))
>>> a
['346', '324', '368']
>>> ' '.join(a)
'346 324 368'

This would not matter of exact format as something like this

z = '346 + 324 - 368 - 368 + 368 + 368 -45 -56- 368'

would still split to this

346 324 368 368 368 368 45 56 368

Using python3.x otherwise you have to import string and convert maketrans line to.... string.maketrans('+-','..')