topic Re: Remove letters and special characters from an alpha numeric string using python in Python Questions

Remove letters and special characters from an alpha numeric string using python

JessicaKirby — Thu, 15 Nov 2012 23:01:40 GMT

Hi All,
I need to find a way to remove all letters and special characters from a string so that all i am left with is numbers using python.
The end goal is to use this code in the python code block in the Calculate Field GP tool.

I have a field called Lease_Num
It contains a string such as ML-26588 , ML 25899, UTLM58778A
So sometimes it has a dash, sometimes it has a space and sometime it has nothing. The Alpha characters can be any length and the numbers can be any length. Sometime their can even be an alpha character at the end of the string...its totally random

I need to strip out the the alpha's and any special characters or spaces from the string to leave me with just the number.

Can someone help me with how I would do this and then tell me how to apply it to the code block on Calculate Field GP tool.

Many thanks!

Re: Remove letters and special characters from an alpha numeric string using python

ChrisSnyder — Sat, 11 Dec 2021 06:20:57 GMT

Soemthing like this would work:

import string
fieldValue = "ML-26588"
for character in fieldValue:
    if character in string.ascii_letters or character in string.punctuation:
        fieldValue = fieldValue.replace(character, "")
print fieldValue

I think it would be better to use something like this in an update cursor though... Somthing like:

#Removes all letters and special characters from a string - hopefully leaving only numbers.
import string, arcpy
updateRows = arcpy.UpdateCursor(myFC)
for updateRow in updateRows:
   fieldValue = updateRow.MY_FIELD
   for character in fieldValue:
      if character in string.ascii_letters or character in string.punctuation:
         fieldValue = fieldValue.replace(character, "")
   updateRows.updateRow(updateRow)
del updateRow, updateRows

Re: Remove letters and special characters from an alpha numeric string using python

Luke_Pinner — Sat, 11 Dec 2021 06:21:00 GMT

There's always more than one way do something 🙂

Here's another

import string
fieldValue = "ML-26588-12-a"
stripChars = fieldValue.translate(None, string.digits)
fieldValue = fieldValue.translate(None, stripChars)
print stripChars
print fieldValue

prints:

ML---a
2658812

And even more 🙂

Re: Remove letters and special characters from an alpha numeric string using python

ChrisSnyder — Fri, 16 Nov 2012 01:56:42 GMT

.translate - I like that!

Re: Remove letters and special characters from an alpha numeric string using python

MikeHunter — Fri, 16 Nov 2012 17:48:51 GMT

A simple 1 liner will do it:

cleanedValue =  ''.join([i for i in fieldValue if i.isdigit()])

good luck,
Mike

Re: Remove letters and special characters from an alpha numeric string using python

curtvprice — Sat, 11 Dec 2021 06:21:03 GMT

... and then tell me how to apply it to the code block on Calculate Field GP tool.

Expression:

ExtractNum(!INFIELD!)

Code block:

def ExtractNum(fieldValue):
  try:
    val = ''.join([i for i in fieldValue if i.isdigit()])
  except:
    val = None
  return val

Re: Remove letters and special characters from an alpha numeric string using python

JessicaKirby — Sat, 11 Dec 2021 06:21:05 GMT

A simple 1 liner will do it:
cleanedValue =  ''.join([i for i in fieldValue if i.isdigit()])
good luck,
Mike

Thank you Mike, this worked like a charm!

Re: Remove letters and special characters from an alpha numeric string using python

shivamparashari — Mon, 03 Feb 2014 03:59:36 GMT

Hi,

I am stuck in the same question and trying to remove the alpha characters from the "House Number" field. The house number can be like - 62/A, A/62, 62A/1 etc. Now, I just want to remove the Alpha Characters only(which can be at any place) and nothing else. Can anyone help me with the code (Python or SQL). 😞

Re: Remove letters and special characters from an alpha numeric string using python

curtvprice — Sat, 11 Dec 2021 06:21:08 GMT

Now, I just want to remove the Alpha Characters only(which can be at any place) and nothing else.

One extremely nice thing about Python is you can easily experiment at an interactive command line and tweak your code to get what you want, for example:

>>> ''.join([i for i in "62/A" if i.isdigit()])
'62'
>>> ''.join([i for i in "62/A" if not i.isalpha()])
'62/'

Can anyone help me with the code (Python or SQL).

SQL is almost always used in ArcGIS to select records - not to calculate fields.

Re: Remove letters and special characters from an alpha numeric string using python

FilipKrál — Sat, 11 Dec 2021 06:21:11 GMT

Hi,
Powerful and flexible function for these kinds of manipulations is the 'sub' function from the 're' (regular expressions) module.
The module is normally installed by default.

import re
re.sub(r'\W', '', "A/62")

See other uses here:
http://docs.python.org/2/howto/regex.html#matching-characters

Re: Remove letters and special characters from an alpha numeric string using python

EricMartinson — Mon, 25 Feb 2019 17:53:30 GMT

Thanks, Mike! It was an agonizing quest before I found your simple answer!

Eric

Re: Remove letters and special characters from an alpha numeric string using python

EricMartinson — Thu, 28 Feb 2019 19:11:09 GMT

Mike, or anyone, are you still out there? Your solution worked perfectly for me in a field calculation a couple days ago. Now, using the same fields in the same database, but a different selection of records, I'm getting an error. I'm too much of a dolt in Python to see why. Here's what I'm getting:

"syntaxerror: encoding declaration in unicode string (<expression>, line 0)" (see below)

At first I thought it might be some characters that were causing the issue (hyphens, slashes, spaces), but eliminating them didn't help.

Any ideas?

Eric