topic Calculate Field based on another field using Python in Python Questions

Calculate Field based on another field using Python

DavidKulpanowski1 — Fri, 03 Aug 2018 19:32:34 GMT

I am working on a TIGER line file of roads in my county in shapefile format (although I am having the same problem with geodatabase format). I am attempting to update a created field named SpeedMPH based on another field. If the field named ROAD_MTFCC is equal to S1200 then update the SpeedMPH field to 25. My code block is written in Python 3.6 and I am running ArcGIS Pro 2.2.1 with the latest updates. My code block is:

def Reclass(fld):
if(ROAD_MTFCC == 'S1200'):
return 25
elif(ROAD_MTFCC == 'S1400'):
return 35
elif(ROAD_MTFCC == 'S1500'):
return 45
elif(ROAD_MTFCC == 'S1640'):
return 55

I then click the green check to verify my code and it is accepted. I click the run button and it runs for a few seconds. When I look at my TIGER line file of roads attribute table the SpeedMPH field is NULL. Nothing was updated.

What am I doing wrong?

Enclosed is a picture of the Calculate field window and a 7zip of my TIGER line shapefile. It is pretty standard Census data.

Re: Calculate Field based on another field using Python

RandyBurton — Sun, 12 Dec 2021 05:09:05 GMT

Pass ROAD_MTFCC to your function, and in your function reference fld.

Reclass(!ROAD_MTFCC!)


def Reclass(fld):

    if(fld == 'S1200'):
        return 25

    #  etc.....‍‍‍‍‍‍‍‍‍

Re: Calculate Field based on another field using Python

DavidKulpanowski1 — Fri, 03 Aug 2018 19:48:52 GMT

Thank you Randy Burton.

That was very helpful. I am posting a screen grab of the answer as it is supposed to look.

Re: Calculate Field based on another field using Python

RandyBurton — Sun, 12 Dec 2021 05:09:08 GMT

You may want to restructure your if/elif/else in your function so that it will always return something - perhaps a zero or 25 for any unknown value.

if (fld == 'S1640'):
  return 55
elif (fld == 'S1500'):
  return 45
elif (fld == 'S1400'):
  return 35
else:  # for S1200 and any other value, just in case
  return 25
‍‍‍‍‍‍‍‍

Re: Calculate Field based on another field using Python

JoshuaBixby — Sun, 12 Dec 2021 05:09:11 GMT

Although if/elif statements can be used to create simple mappings, the statements tend to get cumbersome for anything but the most trivial mappings. The primary mapping type in Python is dict, and it makes for a much more straightforward function in your case:

def Reclass(fld):
    d = {'S1200':25, 'S1400':35, 'S1500':45, 'S1640':55}
    return d.get(fld.upper())‍‍‍

Using the get method takes care of the missing values being passed to the dictionary.

Re: Calculate Field based on another field using Python

NedCake1 — Thu, 01 Apr 2021 17:29:30 GMT

Very Slick! Thanks for the example Josh. Used it to convert some numeric domains to text.

def Reclass(fld): d = { '0':'Unclassified', '1':'Cemetery', '2':'Dock', '3':'Park', '4':'Parkin Lot', '5':'Sign', '6':'Stormwater Treatment Area', '7':'Telecom', '8':'Utility-Water', '9':'Utility-Electric', '10':'Utility-Sewer', '11':'Utility-Gas', '12':'Vacant', '13.1':'Apartment', '13.01':'Single Family Unit', '13.02':'Duplex', '13.03':'Triplex' '13.04':'Quadplex', '13.05':'Mobile Home', '13.06':'Townhouse', '13.07':'Condominium', '13.08':'Prefabricated Home', '13.09':'Abandoned-Dilapidated', '13.11':'Multi-Family', '13.12':'Abandoned Mobile Home', '14':'Commercial', '15':'FSU', '16':'TCC', '17':'FAMU', '18':'Elementary School', '19':'Middle School', '20':'High School', '21':'Religious', '22':'Airport', '23':'Community Center', '24':'Cultural', '25':'General', '26.01':'Govt-City', '26.02':'Govt-County', '26.03':'Govt-State', '26.04':'Govt-Federal', '27':'Hotel', '28':'Industrial', '29':'Medical', '30':'Recreation', '31':'Transportation', '32':'Bar-Shed-Shop', '33':'Delete', '34':'New Building See Notes', '35':'Garage Carport', '36':'Mobile Home Storage', '99':'Re-Review', } return d.get(fld.upper())

Re: Calculate Field based on another field using Python

BlakeTerhune — Thu, 01 Apr 2021 20:54:20 GMT

Dictionary .get() is great! You can also specify a default value (besides None) if the key is not found.