ArcGIS-Python-Code.md

Using python can help automate repetitive tasks in ArcGIS, but getting the code to run can sometimes be very frustrating! Here's a collection of some code/scripts I've used.

##Field Calculator I always seem to have a difficult time performing Attribute Field Calculations. Here's a few tips:

1. The order of operations is controlled by spacing: start loops with 2-spaces, and lines within loops with 4-spaces

###Example converting variable type text numerals to float This script copies numbers stored as a string variable, and converts them to a floating point variable, while converting any null values to '-99.' This syntax only works for ArcGIS versions 10.1 and newer, and I took it from this ESRI page.

Pre-Logic Script Code:

#Define a python function using the syntax 'def <FunctionName>(InputField):'
def update(value):

  #Create a return value variable, and set its value to '-99'
  retValue = -99
  
  #If the Input Value is NOT Null (Python uses the term 'None' for null values), 
  #then convert the Input Value to a Floating type variable, and set it as the return value
  if value is not None:
    retValue = float(value)
  
  #Pass the return value on to the Output Field
  return retValue

[OutputFieldName] =

#Run the above define update function ong the Input Field
update( !InputFieldName!)

###Example reclassifying numerial data with If...Then statement I made this script when I was playing with some data on the distribution of Starbucks in various states. It reclassifies "NULL" values (aka "None" in python syntax) to 1, and leaves existing 0 values as 0

Pre-Logic Script Code:

def Reclass(Starbucks):

  if Starbucks is None:
    return 1

  if Starbucks == 0:
    return 0

[OutputFieldName] =

Reclass( !Starbucks! )

###Example setting values in a new field based on values in an exisiting fields Continuing with the data from above, I wanted to populate a new text field called "Recommend" based on its proximity to exisitng Starbuck locations. The proximity to a Starbucks is already coded in the "Starbucks" field, and for each value in this field I wanted a corresponding recommendation in the "Recommend" field.

Pre-Logic Script Code:

def Update(Starbucks, Recommend):

  if Starbucks == 0:
     Recommend =  "Be ready to make your own cappuccino"
     return Recommend

  if Starbucks == 1:
    Recommend = "You can find a Starbucks, but you will have to drive"
    return Recommend
 
  if Starbucks == 2:
    Recommend = "You can easily find Starbucks coffee"
    return Recommend

[OutputFieldName] =

Update( !Starbucks!, !Recommend! )