Arcpy: Check if a field exists

I was helping a co-worker who needed to check if a field exists in their arcpy script. Since we were located at their computer, I thought I would just do a quick Google search and pull the code off this blog. Seemed logical since I the original purpose was exactly that—to serve as a handy, public place to store code snippets that I use & that others might find handy.

Anyhow, my Google Search on “Node Dangles field Exists” came up with a 9.3 script to check if field index exists. And I also have a 10.0 version but did not come up with the field exists snippet. So here it is:


def fieldExists(inFeatureClass, inFieldName):
  fieldList = arcpy.ListFields(inFeatureClass)
  for iField in fieldList:
    if == inFieldName.lower():
      return True
  return False

ArcMap Field Calculator: Number of parts in multi-part feature

In the last week, I have looked for multi-part features a couple of times. Today, I was looking for multi-part polygons after dealing with the fall-out of a case of Clip Gone Wild as shown below.


I have not found a way to write a query to find these but Field Calculator does allow you to calculate a field’s value to the number of parts.

Using the Python parser, just write the formula (note that case matters): !shape!.partCount


Quick & Dirty python: Converting a text file to audio (.wav)

This is a bit of a tangent but for some crazy reason, I wanted to convert some text to audio so I could listen to it while I drive. A quick Google search left me without any freeware that could handle the 53 page document–there are some cool websites that do text to mp3 like vozme and YAKiToMe! but they didn’t convert the whole document. I then found pyTTS, a python package that serves as a wrapper to the Microsoft Speech API (SAPI) , which has been in version 5 since 2000. But I didn’t easily find a version of pyTTS for python 2.6. So I decided to see if I could roll my own.

As it turns out, getting python to talk using SAPI is relatively easy. Reading a plain text file can be done in a few lines.

from comtypes.client import CreateObject

infile = "c:/temp/text.txt"

engine = CreateObject("SAPI.SpVoice")

f = open(infile, 'r')
theText =


And it wasn’t that much more to have it write out a .wav file:

from comtypes.client import CreateObject

engine = CreateObject("SAPI.SpVoice")
stream = CreateObject("SAPI.SpFileStream")

infile = "c:/temp/text.txt"
outfile = "c:/temp/text4.wav"
stream.Open(outfile, SpeechLib.SSFMCreateForWrite)
engine.AudioOutputStream = stream

f = open(infile, 'r')
theText =



And with that chunk of code, I was able to convert my 54 page document into a 4 hour long .wav file (over 600 MB) that I used another software package to convert to .mp3 (200 MB). The voice is a bit robotic but not too bad, I just hope the content that I converted (a database specification standard) doesn’t put me to sleep while I drive.

Quick & Dirty arcpy: Autopan ArcMap using arcpy

Question: How do I get ArcMap to automatically pan through an area.

As I mentioned in a previous post, I recently had the need to have ArcMap automatically pan through a project area. My first attempt was to print a series of data-driven pages (using a fishnet polygon layer as the index) this but that did not accomplish what I needed so I switched to arcpy, which made the task simple enough. Nothing special or tricky about this code, but just did not find it anywhere else.

The one thing to note is that I have a 1 second pause between pans–this was to allow image tiles to download. You will need to adjust the delay to meet your needs. The toolbox and code can also be downloaded.

import sys,arcpy,datetime
inLayer = sys.argv[1]

def printit(inMessage):
    print inMessage

mxd = arcpy.mapping.MapDocument("CURRENT")

arcpy.MakeFeatureLayer_management(inLayer, "indexLayer")

df = arcpy.mapping.ListDataFrames(mxd)[0]
newExtent = df.extent

iCount = 0
iTotal = (arcpy.GetCount_management("indexLayer").getOutput(0))

for row in cur:
    thisPoly = row.getValue("Shape")
    newExtent.XMin, newExtent.YMin = thisPoly.extent.XMin, thisPoly.extent.YMin
    newExtent.XMax, newExtent.YMax = thisPoly.extent.XMax, thisPoly.extent.YMax
    df.extent = newExtent
    printit("Panned to feature {0} of {1}".format(iCount,iTotal))

del row
del cur

ArcMap Field Calculator: Identifying Unique Cases, Multiple Fields

You may have noticed that this post–ArcMap Field Calculator: Identifying Unique Cases, Single Field–specifies “Single Field”. Yes, that was my version of a cliff-hanger post.

The basic structure I listed in that post can be expanded on to satisfy your needs. The example in my earlier post was case sensitive for example, you could modify it so it treats “a” the same as “A”.

Today’s example groups records into different cases based off the values of two fields, !county_c! and !feature! and required only minor modifications.

The calling line was modified from:




to accommodate passing both values.

The function definition likewise was modified to accept two values, this:

def returnCase(inValue1):


def returnCase(inValue1, inValue2)

And this line was added, creating a list from the two values passed in:

inValue = [inValue1, inValue2]


(Note: The same results could have be achieved by using the original function by creating the list in the calling statement:  returnCase([!county_c!,!feature!] )


caseList = [ ]

def returnCase(inValue1, inValue2):
   inValue = [inValue1, inValue2]
   global caseList

   if not inValue in caseList:

   return caseList.index(inValue)

ArcMap Field Calculator: Text to Double

Received a request yesterday asking how to use the ArcMap Calculator to copy values from a Text field to a Double field using python syntax.  As any good blogger would do, I immediately thought, “Awesome! Someone’s question is the perfect topic for a new blog post”.

The python parser is actually pretty good at casting values on the fly so if the values in your text field (!Day! in my example) are valid values that can be converted to a Double value, it is as simple as just setting the formula to be the text field. In my example case, I wanted to copy the value from !Day! to !DecDay! so I set the formula to be DecDay = !Day!.

That should work fine if you have clean values in your text field. In the example above, you might notice I had a selected set of 3 records that all had numeric values in the !Day! field. When I included the fourth row, which does not have a numeric value in the text field, I get this error message (“There was a failure during processing, check the Geoprocessing Results window for details.” when I use the same formula. Time to add in an error exception.

For more advanced logic, the Field Calculator dialog allows you to use a python function if you check on the “Show Codeblock” option.  In the “Pre-Logic Script Code” area (Seriously, who at ESRI came up with that name?) I entered the following function. If the value in my text field (!Day!) can be cast to a number of type float, that value is returned. If the cast is unsuccessful (IE the value in !Day! is not a number), then I return -99.

def toNum(inValue):
      outValue = float(inValue)
      return outValue
      return -99

Then in the formula portion of the dialog, I call the function, passing the value in the !Day! field: DecDay = toNum(!Day!).

Now, if you would prefer not to set all the records with non-numeric values to be -99 or other error value, not return anything. To do this, I replaced the “return -99” in the original function with a filler line (“doNothing = 4”) since the try block needs an non-empty except clause.

def toNum(inValue):
      outValue = float(inValue)
      return outValue
      doNothing = 4

And that should leave the values in the double field unscathed in your records with non-numeric values in the text field.

Shameless Plug: Check out my other blog posts on using ArcMap’s Field Calculator to calculate geometry and converting a date value to an 8 digit numeric value.

Quicker & Cleaner python recursive folder search

As contributor of the day, Jason Scheirer, pointed out, python has a simple, direct way to browse through the subdirectories of a directory–os.walk

Here is a bare-bones example of using it to print out the subdirectories in a path. The files variable of the 3-tuple is a list of files similar to the dirs variable that I loop through.

Thanks Jason for pointing out something I missed.

import os

theDir = 'c:/temp/'

for root, dirs, files in os.walk(theDir,True,None):
    for idir in dirs:
        print "     directory:   {0}/{1}".format(root,idir)