How to insert character ('-") every time my string changes from text to number and vice versa?

This is an example of a bigger dataframe. Imagine I have a dataframe like this:

import pandas as pd

df = pd.DataFrame({"ID":["4SSS50FX","2TT1897FA"],
                   "VALUE":[13, 56]})

df
Out[2]: 
          ID  VALUE
0   4SSS50FX     13
1  2TT1897FA     56

I would like to insert "-" in the strings from df["ID"] everytime it changes from number to text and from text to number. So the output should be like:

          ID  VALUE
0   4-SSS-50-FX     13
1  2-TT-1897-FA     56

I could create specific conditions for each case, but I would like to automate it for all the samples. Anyone could help me?

Solution

You can use a regular expression with lookarounds.

df['ID'] = df['ID'].str.replace(r'(?<=\d)(?=[A-Z])|(?<=[A-Z])(?=\d)', '-')

The regexp matches an empty string that's either preceded by a digit and followed by a letter, or vice versa. This empty string is then replaced with -.