Extract substrings from the Snippet string in Ultisnips

Question

So I have been working with vim-tex and ultisnips lately.
Let us say the snippet is of the form (\d)pder. It is a 5 character snippet and the first character can be accessed by match.group(1).

But now I want to access substrings of the snippet with unspecified number of characters using certain pattern. For example, if pderxaybzc I want to extract the substring xaybzc by removing pder, so that each character of the output substring can be used within the snippet definition in different places.
I have tried looking for solutions and haven't found any.

Is this feature present in Ultisnips and can the above mentioned be done?

(Thank you in advance)

Answer 1

The following snippet worked out for me:

snippet `pder(\w*)` "Description" rw
\\frac{\\partial^{`!p snip.rv=findSum(match.group(1))`}}{`!p snip.rv=printd("\\partial",match.group(1))`} $0
endsnippet

with

global !p
def findSum(str1): 
    # A temporary str1ing 
    temp = 0
  
    # holds sum of all numbers 
    # present in the str1ing 
    Sum = 0
    icount=0
    # read each character in input string 
    for ch in str1: 
  
        # if current character is a digit 
        if (ch.isdigit()): 
            Sum += int(ch) 
            icount=icount+1
    Sum=Sum+len(str1)-2*icount
    # atoi(temp.c_str1()) takes care 
    # of trailing numbers 
    return Sum

endglobal

I should at that * here would mean that, in the group () it would check for the zero,single or multiple instance of the previous occurring character. So here it checks for multiple alphanumeric, which is just a string.

Also one can use + in place of * if they want at least one character to be present for the expansion of snippet. Like (\w+) would require the snippet to have at least one character to expand.

Edit: The limitation of the code is that the derivative can have only natural number powers of 1 digit.

Answer 2

Simply extend the snippet to (\d)pder(\w*) and handle the second submatch appropriately.