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

Question

I am trying to calculate field test2 with only the numeric values from a string field test. The entire script is like:

def makestr(test)
     list=[]
     for s in test:
         if s.isdigit():
             list.append(s)
     for a in list:
         str=''.join(list)

But I keep getting an error:

Any ideas?

artwork21 · Answer

You are defining the function on the first statement, which needs to end in a ":", e.g.

def makestr(test):

Here is a simple solution:

def makestr(test): 
  try:
    return ''.join(i for i in test if i.isdigit()) 
  except ValueError:
    pass

Martin · Answer

I found also another error. You have to join the a values at the last loop:

def makestr(test):
    l1=[]
    for val in test:
        if val.isdigit():
            l1.append(val)
    return " ".join(l1)

or

def makestr(test):
    l1 =[val for val in test if val.isdigit()]
    return " ".join(l1)

You can join list items without iterating over them. Just use the join fuction with the list as argument.
It is better not to name variables "str" or "list" because thay are python built-in names, which can cause problems.

nmpeterson · Answer

Try this:

def makestr(test):  # Add colon
     numlist = []   # Don't use name "list"
     for s in test:
         if s.isdigit():
             numlist.append(s)
     return ''.join(numlist)  # Return a value

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

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