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If else statement

JamesSmith7

I am modifying a script suggested in a prior thread. http://forums.arcgis.com/threads/90242-Polygon-Centroid?highlight=jsmith0705

I want to be able to select a line, determine if the ARCLENGTH field has a value greater than zero, return that value if greater than zero, if not return the value from the Shape_Length field.

The script runs with no errors or results.

import arcpy  mxd = arcpy.mapping.MapDocument ("CURRENT") df = arcpy.mapping.ListDataFrames (mxd)[0]  lyr = arcpy.mapping.ListLayers(mxd, "Lot_Lines", df)[0]  for lyr in arcpy.mapping.ListLayers(mxd):  tlyr = lyr  dsc = arcpy.Describe(tlyr)  sel_set = dsc.FIDSet  if dsc.shapeType == "Line":   if len(sel_set) > 0: #If ARCLENGTH value > 0           arcpy.AddMessage(str(ARCLENGTH)) #Return ARCLENGTH value   else:    arcpy.AddMessage(str(Shape_Length)) #Return Shape_Length value

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Accepted answers

RichardFairhurst

Why does changing the number 0 to a string '0', change the selection from arcLength to shapeLength? For instance, if len(arcLength) > 0: returns arcLength and if len(arcLength) > '0': returns shapeLength? The ARCLENGTH field is a string and the Shape_Length field is a double.

I didn't write if len(arcLength) > '0':. That is a meaningless piece of code and should return an error, since a it is comparing a number with a string. The alternative you wrote is also wrong. if len(arcLength) > 0: should return arclength even if it is ' ', which you don't want. The version James wrote was if len(arcLength) > 1: and it will not return ' ' through '9', which is also wrong.

I wrote if arcLength > '0':, which compares the string with a string and will return arcLength in all cases except where it is equal to ' ' or '0'. It will return '1' - '9'. Use the code I wrote and you will get the most correct results. (It still could fail if you had values like ' 0' or '00', but I considered that to be too unlikely to add more tests to evaluate.)

All comments

RichardFairhurst

Only add ArcLength when it is greater than '0'. Otherwise, the script should return shapeLength values and add those together.

Then just use the code as written in my post before that. Here is how to make the message only report the totals if they are above 0.

for lyr in arcpy.mapping.ListLayers(mxd):
 dsc = arcpy.Describe(lyr)
 sel_set = dsc.fidSet.replace(";",",")
 if dsc.shapeType == "Polyline" and dsc.fidSet != "":
  cursor = arcpy.da.SearchCursor(lyr, ["OID@", "ARCLENGTH", "Shape_Length"], "OBJECTID IN (" + sel_set + ")")
  arcLengthTot = 0
  shapeLengthTot = 0
  for row in cursor:
   arcLength = row[1]
   shapeLength = row[2]
   if arcLength > '0':
    arcLengthTot += float(arcLength)
    arcpy.AddMessage("ArcLength = " + arcLength)
   else:
    shapeLengthTot += shapeLength
    arcpy.AddMessage("ShapeLength = " + str(shapeLength))
   if arcLengthTot > 0:
    arcpy.AddMessage("ArcLengthTot = " + str(arcLengthTot))
   if shapeLengthTot > 0:
    arcpy.AddMessage("ShapeLengthTot = " + str(shapeLengthTot))
  del row
  del cursor

Both totals messages could print for a given selection is you selected a mix of the two kinds of arcs/shapes as a group.

You could now optionally comment out the individual reported lengths if you want just the totals or leave both individual segment and totals messages. For a single feature the messages would print two times and repeat the same number unless some more logic is added about the sel_set count.

JamesSmith7

Reread my post. After you posted this I made some edits that should be clearer. In the case of ShapeLength, did you want it to add even when ArcLength is greater than '0' or just when arcLength is less than or equal to '0'? I wrote it to do the latter. If you wanted it to do the former the code within the cursor rotuine would be
   if arcLength > '0':
    arcLengthTot += float(arcLength)
    shapeLengthTot += shapeLength
    arcpy.AddMessage("ArcLength = " + arcLength)
   else:
    shapeLengthTot += shapeLength
    arcpy.AddMessage("ShapeLength = " + str(shapeLength))
Edit: Fixed another indent issue.

Only add ArcLength when it is greater than '0'. Otherwise, the script should return shapeLength values and add those together.

RichardFairhurst

Rereading my last post, I realize my statement maybe clear as mud.

I need to add arcLength + arcLength and shapeLength + shapeLength, as two separate expressions.

Reread my post. After you posted this I made some edits that should be clearer. In the case of ShapeLength, did you want it to add even when ArcLength is greater than '0' or just when arcLength is less than or equal to '0'? I wrote it to do the latter. If you wanted it to do the former the code within the cursor rotuine would be

   if arcLength > '0':
    arcLengthTot += float(arcLength)
    shapeLengthTot += shapeLength
    arcpy.AddMessage("ArcLength = " + arcLength)
   else:
    shapeLengthTot += shapeLength
    arcpy.AddMessage("ShapeLength = " + str(shapeLength))

Edit: Fixed another indent issue.

JamesSmith7

Rereading my last post, I realize my statement maybe clear as mud.

I need to add arcLength + arcLength and shapeLength + shapeLength, as two separate expressions.

RichardFairhurst

This is quickly becoming the script that would not go away.

I have read through the help on arithmetic operators. I need to add the selected ArcLength values together and the selected Shape_Length values together. What is the syntax difference in using + for an arithmetic operator and using the + to concatenate fields?

The difference is if the expressions on each side are both strings or both numbers. A mix should trigger an error. So once you have established that you are dealing with an ArcLength that is greater than '0' cast it to a float and then do the addition and then cast back to a string if it has to overwrite the ArcLength field. So to do all of that it should be:

for lyr in arcpy.mapping.ListLayers(mxd):
 dsc = arcpy.Describe(lyr)
 sel_set = dsc.fidSet.replace(";",",")
 if dsc.shapeType == "Polyline" and dsc.fidSet != "":
  cursor = arcpy.da.SearchCursor(lyr, ["OID@", "ARCLENGTH", "Shape_Length"], "OBJECTID IN (" + sel_set + ")")
  arcLengthTot = 0
  shapeLengthTot = 0
  for row in cursor:
   arcLength = row[1]
   shapeLength = row[2]
   if arcLength > '0':
    arcLengthTot += float(arcLength)
    arcpy.AddMessage("ArcLength = " + arcLength)
   else:
    shapeLengthTot += shapeLength
    arcpy.AddMessage("ShapeLength = " + str(shapeLength))
   arcpy.AddMessage("ArcLengthTot = " + str(arcLengthTot))
   arcpy.AddMessage("ShapeLengthTot = " + str(shapeLengthTot))
  del row
  del cursor

JamesSmith7

This is quickly becoming the script that would not go away.

I have read through the help on arithmetic operators. I need to add the selected ArcLength values together and the selected Shape_Length values together. What is the syntax difference in using + for an arithmetic operator and using the + to concatenate fields?

JamesSmith7

Richard,

Thanks for all of your help. I really appreciate the explanations to go along with the examples. I learned a lot during the process.

RichardFairhurst

Why does changing the number 0 to a string '0', change the selection from arcLength to shapeLength? For instance, if len(arcLength) > 0: returns arcLength and if len(arcLength) > '0': returns shapeLength? The ARCLENGTH field is a string and the Shape_Length field is a double.

JamesSmith7

It is another case of the indent being at the wrong level. By indenting as I have above the loop includes the message as each record is processed. Before it only processed once after all rows had been read, so only the last row data was left.

Also, I believe the line that reads if len(arcLength) > 0: should be replaced by the line I have shown above (if arcLength > '0': ) to ensure than even single digit above 0 arclength's are included in the output as an ArcLength.

Why does changing the number 0 to a string '0', change the selection from arcLength to shapeLength? For instance, if len(arcLength) > 0: returns arcLength and if len(arcLength) > '0': returns shapeLength? The ARCLENGTH field is a string and the Shape_Length field is a double.

RichardFairhurst

Thanks Richard. This script is really kicking my butt!

I made another mod to the script to change if arcLength > ' ': to if arcLength > '0':. That will exclude arclengths of ' ' and '0', but include '1'-'9'.

JamesSmith7

It is another case of the indent being at the wrong level. By indenting as I have above the loop includes the message as each record is processed. Before it only processed once after all rows had been read, so only the last row data was left.

Also, I believe the line that reads if len(arcLength) > 0: should be replaced by the line I have shown above (if arcLength > ' ':) to ensure than even single digit arclength's are included in the output as an ArcLength.

Thanks Richard. This script is really kicking my butt!

If I leave if len(arcLength) > '': shapeLength is returned if an arcLength is present or not and if len(arcLength) > 0: either an arcLength value is returned or arcLenth = .

I am going to try and add a second if statement with if len(arcLength) > '': and see if that works.

RichardFairhurst

Using Jake's example, I was unable to get any results. Using, Rich's example, I was able to return either ARCLENGTH or Shape_Length. But, it only returns one record at a time and the record with the largest OID. For instance, if I have 3 Shape_Length records selected, Shape_Length = 302.5 is returned. The script returns only the record with the highest OID value. Any ideas on how to return all three values? Something along the lines of:

Shape_Length = 244.5
Shape_Length = 692.9
Shape_Length = 302.5
for lyr in arcpy.mapping.ListLayers(mxd):
 dsc = arcpy.Describe(lyr)
 sel_set = dsc.fidSet.replace(";",",")
 if dsc.shapeType == "Polyline" and dsc.fidSet != "":
  cursor = arcpy.da.SearchCursor(lyr, ["OID@", "ARCLENGTH", "Shape_Length"], "OBJECTID IN (" + sel_set + ")")
  for row in cursor:
   arcLength = row[1]
   shapeLength = row[2]
   if arcLength > '0':
    arcpy.AddMessage("ArcLength = " + arcLength)
   else:
    arcpy.AddMessage("ShapeLength = " + str(shapeLength))
  del row
  del cursor

It is another case of the indent being at the wrong level. By indenting as I have above the loop includes the message as each record is processed. Before it only processed once after all rows had been read, so only the last row data was left.

Also, I believe the line that reads if len(arcLength) > 0: should be replaced by the line I have shown above (if arcLength > '0': ) to ensure than even single digit above 0 arclength's are included in the output as an ArcLength.

JamesSmith7

Using Jake's example, I was unable to get any results. Using, Rich's example, I was able to return either ARCLENGTH or Shape_Length. But, it only returns one record at a time and the record with the largest OID. For instance, if I have 3 Shape_Length records selected, Shape_Length = 302.5 is returned. The script returns only the record with the highest OID value. Any ideas on how to return all three values? Something along the lines of:

Shape_Length = 244.5
Shape_Length = 692.9
Shape_Length = 302.5

for lyr in arcpy.mapping.ListLayers(mxd):
 dsc = arcpy.Describe(lyr)
 sel_set = dsc.fidSet.replace(";",",")
 if dsc.shapeType == "Polyline" and dsc.fidSet != "":
  cursor = arcpy.da.SearchCursor(lyr, ["OID@", "ARCLENGTH", "Shape_Length"], "OBJECTID IN (" + sel_set + ")")
  for row in cursor:
   arcLength = row[1]
   shapeLength = row[2]
  if len(arcLength) > 0:
   arcpy.AddMessage("ArcLength = " + arcLength)
  else:
   arcpy.AddMessage("ShapeLength = " + str(shapeLength))
  del row
  del cursor

RichardFairhurst

I would have expected an indentation error, but not the name error. Thanks.

It was only logically wrong, not syntactically wrong. The level it was at was possible for other lines of code, but the objects referred to in that particular line only come into existence if you make it to the next indent level.

JamesSmith7

Just indent the del row, rows one more time and that will fix that line. It is at the wrong indent level.

I would have expected an indentation error, but not the name error. Thanks.

RichardFairhurst

I am receiving an error in line 66, del row, rows. The error code is an NameError: name row and rows are not defined. How are they not defined? If I comment the del row, rows statement out the script runs.

import arcpy

mxd = arcpy.mapping.MapDocument ("CURRENT") 
df = arcpy.mapping.ListDataFrames (mxd)[0] 
lyr = arcpy.mapping.ListLayers(mxd, "Lot_Lines", df)[0]
arcpy.AddMessage(lyr.name)
for lyr in arcpy.mapping.ListLayers(mxd):
 dsc = arcpy.Describe(lyr)
 sel_set = dsc.fidSet
 if dsc.shapeType == "Polyline":
  if len(sel_set) > 0:
   sel_set = sel_set.replace(";", ",")
   arcLengthList = []
   shapeLengthList = []
   rows = arcpy.SearchCursor(lyr, "OBJECTID IN (" + sel_set + ")")
   for row in rows:            
    arcLengthList.append(row.ARCLENGTH)
    shapeLengthList.append(row.Shape_Length)
   i = 0
   while i < len(arcLengthList):
    if len(arcLengthList) > 0:
     print arcLengthList
    else:
     print shapeLengthList
    i += 1
    arcpy.AddMessage("Good")
  else:
   rows = arcpy.SearchCursor(lyr, "OBJECTID = " + sel_set)
   for row in rows:
    arcLength = row.ARCLENGTH
    shapeLength = row.Shape_Length
   if len(arcLength) > ' ':
    arcpy.AddMessage("ArcLength = " + arcLength)
   else:
    arcpy.AddMessage("ShapeLength = " + str(shapeLength))
  del row, rows

Just indent the del row, rows one more time and that will fix that line. It is at the wrong indent level.

JamesSmith7

ArcLength is a string field with spaces, so the test will fail unless it converts the string to a number and tests for a space. IN works even if there are no listed object (nothing is selected but no error occurs), a single item, or a list of items, so the else clause is not necessary. = fails and produces an error if there is no listed objectID value or a list, so IN is all you need.

import arcpy

mxd = arcpy.mapping.MapDocument ("CURRENT") 
df = arcpy.mapping.ListDataFrames (mxd)[0] 
lyr = arcpy.mapping.ListLayers(mxd, "Lot_Lines", df)[0]
arcpy.AddMessage(lyr.name)
for lyr in arcpy.mapping.ListLayers(mxd):
 dsc = arcpy.Describe(lyr)
 sel_set = dsc.fidSet
 if dsc.shapeType == "Polyline":
  if len(sel_set) > 0:
   sel_set = sel_set.replace(";", ",")
   arcLengthList = []
   shapeLengthList = []
   rows = arcpy.SearchCursor(lyr, "OBJECTID IN (" + sel_set + ")")
   for row in rows:            
    arcLengthList.append(row.ARCLENGTH)
    shapeLengthList.append(row.Shape_Length)
   i = 0
   while i < len(arcLengthList):
    if len(arcLengthList) > 0:
     print arcLengthList
    else:
     print shapeLengthList
    i += 1
    arcpy.AddMessage("Good")
  else:
   rows = arcpy.SearchCursor(lyr, "OBJECTID = " + sel_set)
   for row in rows:
    arcLength = row.ARCLENGTH
    shapeLength = row.Shape_Length
   if len(arcLength) > ' ':
    arcpy.AddMessage("ArcLength = " + arcLength)
   else:
    arcpy.AddMessage("ShapeLength = " + str(shapeLength))
 del row, rows

JamesSmith7

ArcLength is a string field with spaces, so the test will fail unless it converts the string to a number and tests for a space. IN works even if there are no listed object (nothing is selected but no error occurs), a single item, or a list of items, so the else clause is not necessary. = fails and produces an error if there is no listed objectID value or a list, so IN is all you need.

Richard,

Which statement accounts for the ARCLENGTH field being a string with spaces? Because, if I use your example, I run into a RuntimeError: A column was specified that does not exist, in line 15. for row in rows:, but the error is probably in line 14, the SearchCursor.

import arcpy

mxd = arcpy.mapping.MapDocument ("CURRENT") 
df = arcpy.mapping.ListDataFrames (mxd)[0] 
lyr = arcpy.mapping.ListLayers(mxd, "Lot_Lines", df)[0]
arcpy.AddMessage(lyr.name)

for lyr in arcpy.mapping.ListLayers(mxd):
 dsc = arcpy.Describe(lyr)
 sel_set = dsc.fidSet
 myString = ",".join(sel_set)
 rows = arcpy.da.SearchCursor(lyr, ["OID@", "ARCLENGTH", "Shape_Length"], "OBJECTID IN (" + myString + ")")
 for row in rows:
  arcLength = row.ARCLENGTH
  shapeLength = row.Shape_Length
  if len(arcLength) > 0:
   arcpy.AddMessage("ArcLength = " + arcLength)
  else:
   arcpy.AddMessage("ShapeLength = " + str(shapeLength))
  del row, rows

RichardFairhurst

I was hoping ESRI or the forums contained attitional information. I also have a book that covers Python and the OBJECTID IN operator is not mentioned.

The IN operatot is not a python expression. It is an SQL expression and it is fine to use with all of the databases and the only efficient way to work with lists of values in SQL. It is also fine to use with Python lists, since Python code that uses the IN expression will be found all over the Python forum by every advanced user of Python here. So ignore that recommendation for both SQL and Python. So use the IN operator as shown in my example or Jakes example (as corrected by me for the arcLength field test) and you will get the idea soon enough about what it does.

RichardFairhurst

James,

Here is tech article that discusses selecting multiple values:

http://support.esri.com/en/knowledgebase/techarticles/detail/32024

Try the below. It should work whether you select one line or multiple lines:

mxd = arcpy.mapping.MapDocument("CURRENT")
for lyr in arcpy.mapping.ListLayers(mxd):
    dsc = arcpy.Describe(lyr)
    sel_set = dsc.fidSet
    if dsc.shapeType == "Polyline":
        if len(sel_set) > 1:
            sel_set = sel_set.replace(";", ",")
            arcLengthList = []
            shapeLengthList = []
            rows = arcpy.SearchCursor(lyr, "OBJECTID IN (" + sel_set + ")")
            for row in rows:            
                arcLengthList.append(row.ARCLENGTH)
                shapeLengthList.append(row.shape.length)
            i = 0
            while i < len(arcLengthList):
                if len(arcLengthList) > 1:
                    print arcLengthList
                else:
                    print shapeLengthList
                i += 1
        else:
            rows = arcpy.SearchCursor(lyr, "OBJECTID = " + sel_set)
            for row in rows:
                arcLength = row.ARCLENGTH
                shapeLength = row.shape.length
            if len(arcLength) > ' ':
                print arcLength
            else:
                print shapeLength
    del row, rows

ArcLength is a string field with spaces, so the test will fail unless it converts the string to a number and tests for a space. IN works even if there are no listed object (nothing is selected but no error occurs), a single item, or a list of items, so the else clause is not necessary. = fails and produces an error if there is no listed objectID value or a list, so IN is all you need.

jskinner

mxd = arcpy.mapping.MapDocument("CURRENT")
for lyr in arcpy.mapping.ListLayers(mxd):
    dsc = arcpy.Describe(lyr)
    sel_set = dsc.fidSet
    if dsc.shapeType == "Polyline":
        if len(sel_set) > 1:
            sel_set = sel_set.replace(";", ",")
            arcLengthList = []
            shapeLengthList = []
            rows = arcpy.SearchCursor(lyr, "OBJECTID IN (" + sel_set + ")")
            for row in rows:            
                arcLengthList.append(row.ARCLENGTH)
                shapeLengthList.append(row.shape.length)
            i = 0
            while i < len(arcLengthList):
                if len(arcLengthList) > 1:
                    print arcLengthList
                else:
                    print shapeLengthList
                i += 1
        else:
            rows = arcpy.SearchCursor(lyr, "OBJECTID = " + sel_set)
            for row in rows:
                arcLength = row.ARCLENGTH
                shapeLength = row.shape.length
            if len(arcLength) > 1:
                print arcLength
            else:
                print shapeLength
    del row, rows

JamesSmith7

I was hoping ESRI or the forums contained attitional information. I also have a book that covers Python and the OBJECTID IN operator is not mentioned.

RichardFairhurst

Richard,

Can you point me in the direction to read up on the OBJECTID IN operator? It looks like I may need to select more than one Polyline at a time.

Thanks

ESRI has virtually nothing about it. It's a simple expression. All you need is the field name followed by the word IN and then a comma separated list of correctly typed values within a pair of parentheses. I already gave several examples. Any single value in the list that matches the value of the field for any given record will be included in the selection. You would need to output the python list as a comma separated list in one string. I believe this will work to convert a python list of numbers to a comma separated list:

myList = [12,34,56,78,90]
myString = ",".join(myList)

and then you could make the where clause using the appropriate field delimiters for your database:

'"OBJECTID" IN (' + myString + ')'

In the case of your latest code, I think that the dsc.fidSet is already a string so I think you can use replace to substitute semicolons with commas:

mxd = arcpy.mapping.MapDocument("CURRENT")
for lyr in arcpy.mapping.ListLayers(mxd):
    dsc = arcpy.Describe(lyr)
    sel_set = dsc.fidSet.replace(";",",")
    if dsc.shapeType == "Polyline":
        rows = arcpy.da.SearchCursor(lyr, ["OID@", "ARCLENGTH", "SHAPE@LENGTH"], "OBJECTID IN (" + sel_set + ")")
        for row in rows:
            arcLength = row.[1]
            shapeLength = row.[2]
            if arcLength > ' ':
                print arcLength
            else:
                print shapeLength
    del row, rows

I changed it to a da cursor, since performance is about 10 times faster or more than the old cursor style. You would still need to replace the print methods with AddMessages and I indented the arcLength test so that each line feature will print. The test also will handle single digit arcLength values now that I know it is a string field (although you probably don't have any single digit values in the field).

JamesSmith7

Richard,

Can you point me in the direction to read up on the OBJECTID IN operator? It looks like I may need to select more than one Polyline at a time.

Thanks

JamesSmith7

Dan,

Using your suggestion, would you suggest replacing print arcLength with the following:

def printmessage():
   print 'ARCLENGTH'
if __name__ == '__main__':
   printmessage()

Then repeat for Shape_Length?

Thanks

DanPatterson_Retired

Michael
you can add the code directly to your scripts, or you can import the script...save it in the same folder as the main script

JamesSmith7

Why would a Search Cursor not work to return the ARCLENGTH or Shape_Length value?

cursor = arcpy.da.SearchCursor("Lot_Lines", ["ARCLENGTH", "Shape_Length"])
 for row in cursor:
  row [0] = arcpy.AddMessage(str(row[0]))
  del row
  del cursor

mvolz47

Dan:

How do you call your printMessages.py script from other scripts?

Do you need to add this code directly to other python scripts?

Do you import printMessages into your python script? If so, where does the printMessages.py need to reside with respect to the installed version of python (e.g. C:\Python26\python.exe)?

DanPatterson_Retired

yes you do see http://obidangis.blogspot.ca/2013/06/how-to-print-messages-regardless-of.html

JamesSmith7

The problem is that the field is a String. The empty value for the ARCLENGTH field contains a space. The below code should work:

mxd = arcpy.mapping.MapDocument("CURRENT")
for lyr in arcpy.mapping.ListLayers(mxd):
    dsc = arcpy.Describe(lyr)
    sel_set = dsc.fidSet
    if dsc.shapeType == "Polyline":
        rows = arcpy.SearchCursor(lyr, "OBJECTID = " + sel_set)
        for row in rows:
            arcLength = row.ARCLENGTH
            shapeLength = row.shape.length
        if len(arcLength) > 1:
            print arcLength
        else:
            print shapeLength
    del row, rows

Jake,

The script works using the Python Window within ArcMap. But, not as a Script within a Toolbox. The script runs, but I probably need to replace the print statements with AddMessages.

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