Python exercises the calculation of all characters in the string Fu De and

The second problem: calculating all the numbers in a string and
1. Only lowercase letters and numbers in a string
2. Numbers may or may not be contiguous
3. Sequential numbers are treated as a number

s= ' 1234adg3g11 '
S1 = ""
For I in S:
   If I.isdigit ():
      S1=s1+i
   Else
      s1=s1+ ""
lt = S1.split ("")
m= 0
For a in LT:
   If A.isdigit ():
       M=m+int (a)
Print (m)

* Solve the idea: get the numbers out of the string, separate the numbers from the other characters with if else, and format the other characters and unify them to prepare for the next split. I didn't make it. The traversal of the split () function returns a list of the usages unfamiliar

Python exercises the calculation of all characters in the string Fu De and