Python method for finding a substring within a string

Question

I converted a KML to a feature class and no longer have access to the symbology set in the original KML. I'm trying to re-create this by creating a new field that stores identifying information useful in creating the layer symbology.

There are three different 'keywords' in the original attribute table that would be useful in a control structure that determines the appropriate symbology type. I need to search the string for these keywords, but I'm having trouble.

The sample code below is just to get the control structure working -- I know I need to use an update cursor to change / add field addtributes.

Here is my code:

# Import ESRI Python module
import arcpy
# Declare variables used in this script
#featureClass = r'C:\arbitraryLocationOnDisk'
oldField = 'FolderPath'
newField = 'HabitatType' # Restricted by domain: HabitatType
 # 1. Critical Habitat
 # 2. Corridors and Key Habitat Areas
 # 3. Global IBA's
rows = arcpy.SearchCursor(featureClass)
 for row in rows:
 fieldValue = row.getValue(oldField)
 if fieldValue.find('Global'):
 print 'Global IBA'
 elif fieldValue.find('Corridors'):
 print 'Corridors and Key Habbitat Areas'
 elif fieldValue.find('Critical'):
 print 'Critical Habitat'
 else:
 print 'Unrecognized habitat type: ' + fieldValue
 del fieldValue
except:
 arcpy.GetMessages()
finally:
 del rows

The problem I'm experiencing is that after every single row, I'm getting 'Global IBA' despite the fact that not every row contains the substring 'Global'.

Answer 1

The reason why you're getting 'Global IBA' for every row is that Python's string.find() method returns an integer representing the substring's position within the string, not a boolean. When it can't find the substring, it returns -1, which evaluates to True in your if statement. This could also have the opposite effect; if the string begins with the specified substring, it will return zero, which evaluates to False in your if condition.

Here are some examples:

>>>> 'Global IBA'.find('Global')
0
>>>> bool('Global IBA'.find('Global'))
False
>>>> 'Global IBA'.find('gibberish')
-1
>>>> bool('Global IBA'.find('gibberish'))
True

Since you don't care about the substring's index, it's simpler just to use the 'in' operator:

if 'Global' in fieldValue:
 print 'Global IBA'
elif 'Corridors' in fieldValue:
 print 'Corridors and Key Habbitat Areas'
elif 'Critical' in fieldValue:
 print 'Critical Habitat'
else:
 print 'Unrecognized habitat type: ' + fieldValue

Answer 2

find() returns -1 if no match is found (invalid index of the substring you searched for), so you should be checking against that. In other words, it doesn't have a boolean return value.

Eg. if fieldValue.find('Global') > -1: and so on.