Question

I am trying to using Python’s re.sub() to match a string with an e character and insert curly braces immediately after the e character and after the lastdigit. For example:

12.34e56 to 12.34e{56}
1e10 to 1e{10}

I can’t seem to find the correct regex to insert the desired curly braces. For example, I can properly insert the left brace like this:

>>> import re
>>> x = '12.34e10'
>>> pattern = re.compile(r'(e)')
>>> sub = z = re.sub(pattern, "\1e{", x)
>>> print(sub)
    12.34e{10 # this is the correct placement for the left brace

My problem arises when using two back references.

>>> import re
>>> x = '12.34e10'
>>> pattern = re.compile(r'(e).+($)')
>>> sub = z = re.sub(pattern, "\1e{\2}", x)
>>> print(sub)
    12.34e{} # this is not what I want, digits 10 have been removed

Can anyone point out my problem? Thanks for the help.

Answer 1

re.sub(r'e(\d+)', r'e{\1}', '12.34e56')

returns '12.34e{56}'

or, the same result but different logic (don’t replace e with e):

re.sub(r'(?<=e)(\d+)', r'{\1}', '12.34e56')