topic Mid() function in Python in ArcGIS API for Python Questions

Mid() function in Python

SLouq — Thu, 31 Oct 2019 17:55:30 GMT

I am trying to use the Python Mid() function to return strings starting at the 5th character.

I have tried

!STR_NAME!.Mid(5:20)

but that gives me a traceback error

Can someone point me in the right direction?

Thanks

Re: Mid() function in Python

JoeBorgione — Sun, 12 Dec 2021 09:00:37 GMT

Never heard of the mid() functin and couldn't find it with dr. google.

myString = 'abcdefghijklmnopqrstuvwxyz'
x = myString[5:20]
print(x)
#returns 'fghijklmnopqrst'‍‍‍‍

This works for me...

Re: Mid() function in Python

SLouq — Thu, 31 Oct 2019 18:45:58 GMT

how do I use that expression on a Field in ArcGIS Pro so it returns values starting at the 5th character?

Re: Mid() function in Python

DanPatterson_Retired — Sun, 12 Dec 2021 09:00:40 GMT

Slice lesson

# ---- python slicing... 

b = "abcdefghijklmnopqrstuvwxyz"

str(b)[5:20]
'fghijklmnopqrst'

str(b)[5:]
'fghijklmnopqrstuvwxyz'

str(b)[-5:]
'vwxyz'

str(b)[:5]
'abcde'

# ---- why use str????

str(None)[:2]
'No'

None[:2]
Traceback (most recent call last):

  File "<ipython-input-18-5a2d59b27828>", line 1, in <module>
    None[:2]

TypeError: 'NoneType' object is not subscriptable‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Re: Mid() function in Python

JoeBorgione — Thu, 31 Oct 2019 19:26:04 GMT

See Dan's suggestions below... or:

str(!FieldName!)[5:20]‍‍‍

resources for you: Cutting and slicing strings in Python - Python Central , Python str() - Python Standard Library

Re: Mid() function in Python

DanPatterson_Retired — Thu, 31 Oct 2019 19:39:22 GMT

as per the lesson... 'b' is anything

like str(!STR_NAME!)[5:20]

Re: Mid() function in Python

SLouq — Thu, 31 Oct 2019 19:45:46 GMT

Thanks guys! I got it to execute but it erased more chars than I wanted. Now I just have to re run the models and change the parameters around when I get to this point.

Re: Mid() function in Python

JoeBorgione — Thu, 31 Oct 2019 19:59:38 GMT

Sometimes you just need to fiddle with the indexes to get it just right...

Re: Mid() function in Python

SLouq — Thu, 31 Oct 2019 20:26:06 GMT

That program is buggy as hell. I started my whole model again from the beginning and it stopped when it got to this part with the same error

but yet it worked when I tried it while we were discussing in this thread.

Re: Mid() function in Python

JoeBorgione — Sun, 12 Dec 2021 09:00:43 GMT

Indexes can have a sense of humor. Consider:

myString = 'abcdefg'

str(myString)[1:3]
#'bc' what I really wanted was 'bcd' so what I should have used is:

str(myString)[1:4]
#'bcd'

len(myString)
#7

myString[7]

#Traceback (most recent call last):

  #File "<ipython-input-12-4e9d2e9a673c>", line 1, in <module>
    #myString[7]

#IndexError: string index out of range
‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

When you want specific characters out of a string, you need to really consider which ones you want....

Re: Mid() function in Python

DanPatterson_Retired — Thu, 31 Oct 2019 21:31:55 GMT

do it manually (assuming that you have to do this whole process many times)

get it right, then put in the model in order to rule out other stuff like overwriting outputs etc etc.

The error message would also help.

Also python is 0 based so a[:5] will slice the 0, 1, 2, 3, 4 characters, hence :5 means beyond the 5th character

a[5:10] means beyond the 5th and up to, but not including the 10th (5, 6, 7, 8, 9), that is, 5 characters (10 - 5)

Re: Mid() function in Python

SLouq — Fri, 01 Nov 2019 12:45:43 GMT

Thanks for helping me guys!