topic Re: 'IF' Python Script Tool in Geoprocessing Questions

'IF' Python Script Tool

Corey_C_Denninger — Wed, 08 Sep 2010 16:37:16 GMT

I need to mimic an Excel formula as an ArcGIS script tool (I will run many times on similar fields). It includes the following:
-1 feature class:   'gp.GetParameterAsText(0)'
-3 input fields:   (Z, AF, T)   'gp.GetParameterAsText(1), (2), & (3)'
-1 output field:   'gp.GetParameterAsText(4)'

In Excel, the formula looks like this:
=IF(AND(Z>0,AF>0),SUM(T+Z+AF),IF(AND(Z>0,AF<0),SUM(T+Z),IF(AND(Z<0,AF>0),SUM(T+AF),T)))

In plain words, it is saying:
If the first condition is met, sum these 3 fields together and populate output field
If the second condition is met, sum these 2 fields together and populate output field
If the third condition is met, sum these 2 fields together and populate output field
If none are met, populate output field with field 'T' value.

I am somewhat familiar with Python, but I am struggling with this one. Any help is appreciated. Thank you.

Re: 'IF' Python Script Tool

DanPatterson_Retired — Sat, 11 Dec 2021 15:25:44 GMT

IF(AND(Z>0,AF>0),SUM(T+Z+AF),IF(AND(Z>0,AF<0),SUM (T+Z),IF(AND(Z<0,AF>0),SUM(T+AF),T)))

given Z, AF and T as variables, written explicitly

....stuff before
if (Z > 0) and (AF > 0):
  x = sum( [T, Z, AF] )    #or x = T + Z + AF
elif (Z > 0) and (AF < 0):
  x = sum( [T, Z ] )         #or x = T + Z
elif (Z < 0) and (AF > 0): 
  x = sum( [T, AF] )        #or x = T + AF
else:
  x = T
....
stuff after

you sum lists, ie.
>>> a = [1,2,3]
>>> sum(a)
6
>>>

Re: 'IF' Python Script Tool

LoganPugh — Sat, 11 Dec 2021 15:25:46 GMT

This should be a piece of cake in Python:

Read in your parameters

Get an UpdateCursor from the feature class

For each row in the cursor, do the same logic (psuedo-code):

if [condition 1]: # first condition to check
  [set field value]
elif [condition n]: # you'll have several instances of this for every other condition
  [set field value]
else: # no other conditions matched
  [set field value]
[update the row]
[move to the next row]

Clean up references to row and cursor

Re: 'IF' Python Script Tool

Corey_C_Denninger — Sat, 11 Dec 2021 15:25:49 GMT

I think I am close (with your help of course); but what do you think is wrong with this? It runs without completing, on a relativley small sample.

FC = gp.GetParameterAsText(0)
Z = gp.GetParameterAsText(1)
AF = gp.GetParameterAsText(2)
T = gp.GetParameterAsText(3)
Outfield = gp.GetParameterAsText(4)

cur = gp.UpdateCursor(FC)
row = cur.Next()


while row:
      if (Z > 0) and (AF > 0):
            Outfield = T + Z + AF    #or = sum( [T, Z, AF] )
      elif (Z > 0) and (AF < 0):
            Outfield = T + Z         #or = sum( [T, Z ] )
      elif (Z < 0) and (AF > 0):
            Outfield = T + AF        #or = sum( [T, AF] )
      else:
            Outfield = T
del cur

Re: 'IF' Python Script Tool

DanPatterson_Retired — Sat, 11 Dec 2021 15:25:51 GMT

change the
row = cur.Next() to row = cur.next() if using 10

while row:
      if (Z > 0) and (AF > 0):
            Outfield = T + Z + AF    #or = sum( [T, Z, AF] )
      elif (Z > 0) and (AF < 0):
            Outfield = T + Z         #or = sum( [T, Z ] )
      elif (Z < 0) and (AF > 0):
            Outfield = T + AF        #or = sum( [T, AF] )
      else:
            Outfield = T
      row = cur.next()   # <-------------missing the move to the next row

Re: 'IF' Python Script Tool

LoganPugh — Sat, 11 Dec 2021 15:25:54 GMT

I think I am close (with your help of course); but what do you think is wrong with this? It runs without completing, on a relativley small sample.

FC = gp.GetParameterAsText(0)
Z = gp.GetParameterAsText(1)
AF = gp.GetParameterAsText(2)
T = gp.GetParameterAsText(3)
Outfield = gp.GetParameterAsText(4)

cur = gp.UpdateCursor(FC)
row = cur.Next()


while row:
      if (Z > 0) and (AF > 0):
            Outfield = T + Z + AF    #or = sum( [T, Z, AF] )
      elif (Z > 0) and (AF < 0):
            Outfield = T + Z         #or = sum( [T, Z ] )
      elif (Z < 0) and (AF > 0):
            Outfield = T + AF        #or = sum( [T, AF] )
      else:
            Outfield = T
del cur

All you're currently doing is setting the value of the Outfield variable. You need to be setting the value of the field itself, and then updating the row. Since your field name is a variable, use the SetValue command to set the field's value, and use the UpdateRow command to actually commit the change to the database. And like Dan mentioned, remember to move to the next row before the next iteration.

Re: 'IF' Python Script Tool

DanPatterson_Retired — Wed, 08 Sep 2010 18:58:08 GMT

grief...you are right
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//000v000000nv000000.htm
provides an example

Re: 'IF' Python Script Tool

Corey_C_Denninger — Sat, 11 Dec 2021 15:25:57 GMT

Thank you for the assistance. With the modifications (below), I now get an error when running the script tool. Am I close here? Any help is appreciated. Thanks.

FC = gp.GetParameterAsText(0)
Z = gp.GetParameterAsText(1)
AF = gp.GetParameterAsText(2)
T = gp.GetParameterAsText(3)
Outfield = gp.GetParameterAsText(4)

cur = gp.UpdateCursor(FC)
row = cur.Next()


while row:
      if (Z > 0) and (AF > 0):
            row.SetValue(Outfield, T + Z + AF)  #or = sum( [T, Z, AF] )
            cur.UpdateRow(row)
      elif (Z > 0) and (AF < 0):
            row.SetValue(Outfield, T + Z)         #or = sum( [T, Z ] )
            cur.UpdateRow(row)
      elif (Z < 0) and (AF > 0):
            row.SetValue(Outfield, T + AF)        #or = sum( [T, AF] )
            cur.UpdateRow(row)
      else:
            row.SetValue(Outfield, T)
            cur.UpdateRow(row)
      row = cur.Next()
del cur

Re: 'IF' Python Script Tool

DanPatterson_Retired — Wed, 08 Sep 2010 19:31:11 GMT

With respect...and sensing a bit of anticipation on your part...mind readers we are not...what is the error message?
version of ArcMap?
version 9.x operates differently than 10 for example UpdateRow in 9.3 is updateRow in version 10 as is the setValue method

Re: 'IF' Python Script Tool

LoganPugh — Sat, 11 Dec 2021 15:25:59 GMT

Try creating a variable to store the value you're calculating in the SetValue command instead of doing the calculation in-line. I don't know why, but this appears to be a problem with some ESRI arcgisscripting commands.

for example:

      if (Z > 0) and (AF > 0):
            val = T + Z + AF #or = sum( [T, Z, AF] )
            row.SetValue(Outfield, val)
            cur.UpdateRow(row)

Also, I don't know what T, Z and AF are, but since we're only getting them at the beginning of the script, there's no reason to do the calculations inside the while loop since the result is going to be the same every time.

Or did you mean to be reading the values of T Z and AF from each row instead of as parameters? That's different.

Re: 'IF' Python Script Tool

DanPatterson_Retired — Wed, 08 Sep 2010 19:53:17 GMT

Logan I think you have nailed it...one of the problems in not seeing a whole script.
Since the parameters are field names, then obviously you have to get the value from the field as indicated in the example scripts
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//002z0000001q000000.htm
which means that the T, Z and AF need to be defined as "getValue" lines right after the while statement

Re: 'IF' Python Script Tool

Corey_C_Denninger — Thu, 09 Sep 2010 12:07:25 GMT

Hey Dan - Yea, sorry about that. I assumed the error would be in my revised script and not related to my version, etc. Seems like a string vs. text issue (perhaps), but all field types in the layer are correct (double). Thank you for your efforts.

ArcGIS 9.3.1
Python 2.5

ERROR:
<type 'exceptions.RuntimeError'>: ERROR 999999: Error executing function.
The value type is incompatible with the field type. [TOTFUNC_09]
Failed to execute (PopTool)

As far as not seeing the whole script, all I have so far for a script is what I pasted in my previous posts. If you look at my original (1st) post, it should help clairify my goals. Essentially the final script tool should compare 3 fields in each row of a feature class table and place a value in the output field based on those conditions placed within the script. Z, AF, T, are essentially numeric (double) fields to be compared to each other.

Re: 'IF' Python Script Tool

Corey_C_Denninger — Sat, 11 Dec 2021 15:26:02 GMT

Revised script. Still errors, but from the advice posted, it seems a bit closer.

import sys, string, os, math, arcgisscripting
gp = arcgisscripting.create(9.3)
gp.OverWriteOutput = 1


FC = gp.GetParameterAsText(0)
Z = gp.GetParameterAsText(1)
AF = gp.GetParameterAsText(2)
T = gp.GetParameterAsText(3)
Outfield = gp.GetParameterAsText(4)

cur = gp.UpdateCursor(FC)
row = cur.Next()


while row:
      if row.GetValue == (Z > 0) and (AF > 0):
            row.SetValue(Outfield, T + Z + AF)  #or = sum( [T, Z, AF] )
      elif row.GetValue == (Z > 0) and (AF < 0):
            row.SetValue(Outfield, T + Z)         #or = sum( [T, Z ] )
      elif row.GetValue == (Z < 0) and (AF > 0):
            row.SetValue(Outfield, T + AF)        #or = sum( [T, AF] )
      else:
            row.SetValue(Outfield, T)
            
      cur.UpdateRow(row)
      row = cur.Next()
del cur

ERROR: <type 'exceptions.RuntimeError'>: ERROR 999999: Error executing function.
The value type is incompatible with the field type. [TOTFUNC_09]
Failed to execute (PopTool).

Re: 'IF' Python Script Tool

LoganPugh — Sat, 11 Dec 2021 15:26:04 GMT

Try the following code. I changed the names of the variables you're using to read in the parameters, from what I understand these are the field names, not the field values.

Also when you use GetValue() you have to specify which field you're getting the value from. And since we want to read in all three values for each row I put three GetValue statements at the top of the while loop, storing each in a variable (T, Z, and AF).

Finally, as I mentioned before I used a variable named "val" to store the results of the calculation before using it in SetValue. Some ESRI commands don't like in-line expression evaluation for some reason -- may not be the case here but it's better programming/debugging practice to do it this way anyways.

import sys, string, os, math, arcgisscripting
gp = arcgisscripting.create(9.3)
gp.OverWriteOutput = 1


FC = gp.GetParameterAsText(0)
Z_fld = gp.GetParameterAsText(1)
AF_fld = gp.GetParameterAsText(2)
T_fld = gp.GetParameterAsText(3)
Outfield = gp.GetParameterAsText(4)

cur = gp.UpdateCursor(FC)
row = cur.Next()


while row:
    Z = row.GetValue(Z_fld)
    AF = row.GetValue(AF_fld)
    T = row.GetValue(T_fld)
    if (Z > 0) and (AF > 0):
        val = T + Z + AF    #or = sum( [T, Z, AF] )
    elif (Z > 0) and (AF < 0):
        val = T + Z         #or = sum( [T, Z ] )
    elif (Z < 0) and (AF > 0):
        val = T + AF        #or = sum( [T, AF] )
    else:
        val = T
    row.SetValue(Outfield, val)
    cur.UpdateRow(row)
    row = cur.Next()
del row
del cur

Re: 'IF' Python Script Tool

Corey_C_Denninger — Thu, 09 Sep 2010 15:03:40 GMT

Logan - So far so good. I have been testing on a small sample and it is good so far. Thanks for all the assistance. I realized after I posted my previous, that the GetValue needed an object in the (). I see how you used 'val' and it makes sense and runs pretty quickly. I really do appreciate the help.

So no way to 'credit' posts or award points anymore? Mark as answered or complete?

Re: 'IF' Python Script Tool

LoganPugh — Thu, 09 Sep 2010 15:08:23 GMT

Logan - So far so good. I have been testing on a small sample and it is good so far. Thanks for all the assistance. I realized after I posted my previous, that the GetValue needed an object in the (). I see how you used 'val' and it makes sense and runs pretty quickly. I really do appreciate the help.

So no way to 'credit' posts or award points anymore? Mark as answered or complete?

Good to hear it works! And yeah, I think they omitted the "mark as answered" stuff when they launched the new forums. No biggie. I like the way StackOverflow/Stack Exchange does it better anyway. Check out http://gis.stackexchange.com/

Re: 'IF' Python Script Tool

IbraheemKhan1 — Mon, 15 Aug 2011 03:52:41 GMT

Hi Logan and Dan,

I have found this post very helpful to get IF statements work in python script. Tried to use almost similar approach as used in the thread but each time computation fails. Unable to write files in the same loop. Any help would be deeply appreciative to fix my code below:

try:
for k in range(0,11):
     for l in range(0,11):
         str_fin="oc_lyr"+str(l+1)
             if (t(l)<=nt(k)) and (b(l)>=nb(k)):
                val = oc_lyr(l)*(nb(k)-nt(k))
             elif (t(l)<=nt(k)) and (b(l)>nt(k)):
                val = oc_lyr(l)*(b(l)-nt(k))
             elif (t(l)>nt(k)) and (b(l)<nb(k)):
                val = oc_lyr(l)*(b(l)-t(l))
             elif (t(l)<nb(k)) and (b(l)>=nb(k)):
                val = oc_lyr(l)*(nb(k)-t(l))

except:
print "failed"