Extracting numbers from string field but omit some unnecessary cells using Python Parser of ArcMap Field Calculator?

Question

I refer to Extracting numbers from string field using Python Parser of ArcMap Field Calculator?

The script above works fine for me, but I have to develop it a little. What I want is just to omit values without numbers. As you see in the table TEXTSTRING field with ID = 10 got only letters, it's Ok if Python leaves it empty, I just want make it go through all values in table.

target column is test_srednica2

Below you see my attempt :/

def makestr(TEXTSTRING):

   lis = []
   for i in TEXTSTRING:

      if i.isdigit():
           lis.append(i)
      elif i.isalpha():
           continue


   return ''.join(lis)

---

Below i put code which has filled field "test_srednica2" As you see in table it is working until row "13" there is value "woc". There is no number so i think that`s why this function stops.

I want my function leave cells with letters only, and go throught all the others.

If you look on row "11" you see its going throught even if value is "<Null>" its OK for me.

def makestr(TEXTSTRING):

    lis = []
    for i in TEXTSTRING:

    if i.isdigit():
         lis.append(i)



    return ''.join(lis)

Answer 1

You want the code not to stop when input is Null or only letters?

Try:

def extractNumbers(sometextfield):
    if (sometextfield is not None and any(char.isdigit() for char in sometextfield)):
        return int(''.join([str(i) for i in sometextfield if i.isdigit()]))
    else:
        return None #Or 0 or whatever you want

Call with:

extractNumbers( !Textfield!)