Damian Abbott - 5 months ago 23

Python Question

I am getting strings from a website regarding mathematical equations, when there is a fraction the string it return is '\frac{number1}{number2}'

What I want to do is replace the \frac{}{} and make it for example from '\frac{1}{2}' to '(1)/(2)'

I assumed that re.groups would help with this and tried

`>>> import re`

>>> s = '\\frac{1}{2}'

>>> print(s)

\frac{1}{2}

>>> m = re.match(r'\frac{(\w+)}{(\w+)}',s)

>>> m.groups()

('1', '2')

>>> f = s.replace('\\frac{{}}{{}}'.format(m.group(1), m.group(2)), '{}{}{}{}{}'.format('(', m.group(1), ')/(', m.group(2), ')'))

>>> print(f)

\frac{1}{2}

I still get \frac{1}{2}

Am I going about this all wrong? Or is there an easier way to do this, or did I make a mistake? I cannot figure it out whatsoever

Also sometimes there is more than one in a string such as

'\frac{1}{2}\sqrt{3} + 3\frac{1}{3}'

Just trying to replace those parts of the string with a more readable version

Answer

Let's leverage the `re.sub`

function, which will replace all matches in the string.

For the `\frac`

case, let's use the following as are regex pattern:

```
patt = r'\\frac\{(\w+)\}\{(\w+)\}'
```

We have to escape the leading `\`

in front of `frac`

, and `{`

and `}`

are metacharacters, so we escape those, too.

So we can now just do `parsed_s = re.sub(patt, r'(\1)/(\2)', s)`

where `s`

is the source string. This will replace all of the matches in the string with the desired format.