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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

MikeVolz

Try adding some print statements to understand what is actually occurring with your script.

print("The describe statement is returning " + dsc) - You mau need to convert dsc to a string if it is not by default a string

If that returns an expected item then I would continue to add print statements at each critical step to ensure you are getting the expected results.

Please provide results of your print statements so I can further assist you.

JakeSkinner

Hi James,

If this is a feature class, try the following below. If this is a shapefile, you will have to update the SearchCursor to use FID instead of OBJECTID.

for lyr in arcpy.mapping.ListLayers(mxd):
    tlyr = lyr
    dsc = arcpy.Describe(tlyr)
    sel_set = dsc.fidSet
    if dsc.shapeType == "Polyline":
        rows = arcpy.SearchCursor(tlyr, "OBJECTID = " + sel_set)
        for row in rows:
            arcLength = row.ARCLENGTH
            shapeLength = row.shape.length
        if arcLength > 0:
            print arcLength
        else:
            print shapeLength
        del row, rows

JamesSmith7

Hi James,

If this is a feature class, try the following below. If this is a shapefile, you will have to update the SearchCursor to use FID instead of OBJECTID.

for lyr in arcpy.mapping.ListLayers(mxd):
    tlyr = lyr
    dsc = arcpy.Describe(tlyr)
    sel_set = dsc.fidSet
    if dsc.shapeType == "Polyline":
        rows = arcpy.SearchCursor(tlyr, "OBJECTID = " + sel_set)
        for row in rows:
            arcLength = row.ARCLENGTH
            shapeLength = row.shape.length
        if arcLength > 0:
            print arcLength
        else:
            print shapeLength
        del row, rows

Jake and Michael,

I am using a feature class. The script runs with no errors or results. I am going to try and adjust the SearchCursor and see what happens.

JamesSmith7

Why would changing the SearchCursor to arcpy.da.SearchCursor return an SQL error, whereas, arcpy.SearchCursor does not? I thought the only difference was arcpy.da.SearchCursor was more efficient?

JakeSkinner

Take a look at the help links. The arcpy.da.SearchCursor is formatted differently.

arcpy.SearchCursor
http://resources.arcgis.com/en/help/main/10.2/index.html#//018v00000050000000

arcpy.da.SearchCursor
http://resources.arcgis.com/en/help/main/10.2/index.html#//018w00000011000000

Can you post the exact code you're using in ArcMap?

JamesSmith7

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 == "Polyline":
  rows = arcpy.da.SearchCursor(tlyr, "OBJECTID = " + sel_set)
  for row in rows:
   arcLength = row.ARCLENGTH
   shapeLength = row.Shape_Length
  if arcLength > 0:
   print arcLength
  else:
   print shapeLength
  del row
  del rows

The error is in line 32, for row in rows: RuntimeError: An invalid SQL statement was used. I know the select Object ID works, because it changes values depending on the feature selected.

JakeSkinner

Check the name of your OBJECTID field (right-click on layer > Properties > Fields tab). It may be OID, or OBJECTID1.

JakeSkinner

Also, change arcpy.da.SearchCursor, to arcpy.SearchCursor.

JamesSmith7

Check the name of your OBJECTID field (right-click on layer > Properties > Fields tab). It may be OID, or OBJECTID1.

The field is named OBJECTID. Changing the cursor back to arcpy.SearchCursor eliminates the SQL Error. But, the script runs with no results.

MikeVolz

Have you checked to see if some of your earlier statements are getting the desired results such as the Describe?

Can you get a length of your sel_set to see if that is returning values?

JamesSmith7

Have you checked to see if some of your earlier statements are getting the desired results such as the Describe?

Can you get a length of your sel_set to see if that is returning values?

Michael,

I have used the arcpy.AddMessage. I noticed that when the AddMessage is inserted after the variables it returns the value. But, when I use the AddMessage after the sel_set = dsc.fidSet, the value is returned three times. Which is odd. I need to research why the value is returned three times.

RichardFairhurst

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 == "Polyline":
  rows = arcpy.da.SearchCursor(tlyr, "OBJECTID = " + sel_set)
  for row in rows:
   arcLength = row.ARCLENGTH
   shapeLength = row.Shape_Length
  if arcLength > 0:
   print arcLength
  else:
   print shapeLength
  del row
  del rows

The error is in line 32, for row in rows: RuntimeError: An invalid SQL statement was used. I know the select Object ID works, because it changes values depending on the feature selected.

When you switched back to the original cursor type you got no records because your where clause needs to use the IN operator not the = operator.

The error using the new arcpy.da cursor is due to the cursor declaration syntax being different. With the arcpy data access (arcpy.da) cursor you have to supply a mandatory field name list prior to defining an optional where clause. Your code has no field list. At a minimum the field list would have to include OBJECTID, ARCLENGTH and Shape_Length. So this code:

rows = arcpy.da.SearchCursor(tlyr, "OBJECTID = " + sel_set)

should be changed to this code:

rows = arcpy.da.SearchCursor(tlyr, ["OID@", "ARCLENGTH", "SHAPE@LENGTH"], "OBJECTID IN (" + sel_set +")")

OID@ makes sure you get the correct ObjectID field name reference, regardless of the database. Possibly SHAPE@LENGTH should be Shape_Length, depending on whether you want to access a geodatabase length field or the actual shape geometry length. You also do not have to use field names again after getting the cursor. You can use numbers to represent the fields. So that means the code beyond that line could also change to:

  rows = arcpy.da.SearchCursor(tlyr, ["OID@", "ARCLENGTH", "SHAPE@LENGTH"], "OBJECTID IN (" + sel_set + ")")
  for row in rows:
   arcLength = row.[1]
   shapeLength = row.[2]
  if arcLength > 0:
   print arcLength
  else:
   print shapeLength
  del row
  del row

JamesSmith7

Why are your rows numbered 1 and 2? Should they be 0 and 1. Since, python normally begins the numbering sequence with zero.

When you switched back to the original cursor type you got no records because your where clause needs to use the IN operator not the = operator.

The error using the new arcpy.da cursor is due to the cursor declaration syntax being different. With the arcpy data access (arcpy.da) cursor you have to supply a mandatory field name list prior to defining an optional where clause. Your code has no field list. At a minimum the field list would have to include OBJECTID, ARCLENGTH and Shape_Length. So this code:

rows = arcpy.da.SearchCursor(tlyr, "OBJECTID = " + sel_set)

should be changed to this code:

rows = arcpy.da.SearchCursor(tlyr, ["OID@", "ARCLENGTH", "SHAPE@LENGTH"], "OBJECTID IN (" + sel_set +")")

OID@ makes sure you get the correct ObjectID field name reference, regardless of the database. Possibly SHAPE@LENGTH should be Shape_Length, depending on whether you want to access a geodatabase length field or the actual shape geometry length. You also do not have to use field names again after getting the cursor. You can use numbers to represent the fields. So that means the code beyond that line could also change to:
  rows = arcpy.da.SearchCursor(tlyr, ["OID@", "ARCLENGTH", "SHAPE@LENGTH"], "OBJECTID IN (" + sel_set + ")")
  for row in rows:
   arcLength = row.[1]
   shapeLength = row.[2]
  if arcLength > 0:
   print arcLength
  else:
   print shapeLength
  del row
  del row

JamesSmith7

Thanks for the explanations, information, and suggested script.

I want to use the Shape_Length field, which is the actual geometry length.

The script runs with added arcpy.AddMessages throughout. Yet, the script does not print the ARCLENGTH or Shape_Length value.

When you switched back to the original cursor type you got no records because your where clause needs to use the IN operator not the = operator.

The error using the new arcpy.da cursor is due to the cursor declaration syntax being different. With the arcpy data access (arcpy.da) cursor you have to supply a mandatory field name list prior to defining an optional where clause. Your code has no field list. At a minimum the field list would have to include OBJECTID, ARCLENGTH and Shape_Length. So this code:

rows = arcpy.da.SearchCursor(tlyr, "OBJECTID = " + sel_set)

should be changed to this code:

rows = arcpy.da.SearchCursor(tlyr, ["OID@", "ARCLENGTH", "SHAPE@LENGTH"], "OBJECTID IN (" + sel_set +")")

OID@ makes sure you get the correct ObjectID field name reference, regardless of the database. Possibly SHAPE@LENGTH should be Shape_Length, depending on whether you want to access a geodatabase length field or the actual shape geometry length. You also do not have to use field names again after getting the cursor. You can use numbers to represent the fields. So that means the code beyond that line could also change to:
  rows = arcpy.da.SearchCursor(tlyr, ["OID@", "ARCLENGTH", "SHAPE@LENGTH"], "OBJECTID IN (" + sel_set + ")")
  for row in rows:
   arcLength = row.[1]
   shapeLength = row.[2]
  if arcLength > 0:
   print arcLength
  else:
   print shapeLength
  del row
  del row

MikeVolz

How many features do you have in your target feature class?

If you print out the fidset, are all of these features included in the semicolon-delimited string?

Can you post the results of printing the fidset from your dsc object?

RichardFairhurst

How many features do you have in your target feature class?

If you print out the fidset, are all of these features included in the semicolon-delimited string?

Can you post the results of printing the fidset from your dsc object?

If the fidset is delimited with semicolons it will have to be changed so that the fid values are delimited by commas for the where clause SQL to work. The SQL IN operator only works with lists of values separated by commas. Nothing in SQL works with semicolon separated lists.

JamesSmith7

How many features do you have in your target feature class?

If you print out the fidset, are all of these features included in the semicolon-delimited string?

Can you post the results of printing the fidset from your dsc object?

The feature class has over a million records.

Printing that many records will take quite a while.

The arcpy.AddMessage("Continue") value was returned.

MikeVolz

James:

Can you create a feature class with a small subset of features (say 10) and then print out the fidset?

It appears from Richard's last post that the semi-colon delimited string will need to be converted to a comma separated list. You shouldbe able to find python methods to easily perform that process.

RichardFairhurst

The feature class has over a million records.

Printing that many records will take quite a while.

The arcpy.AddMessage("Continue") value was returned.

If there are a million FID values placed within the IN clause I don't know that there won't be an error. Try it on a much smaller set first. I suspect the cursor won't accept a string that big that it could pass to the query parser and performance would be horrible.

If it is going to process the entire table don't include a where clause. If it is a selection based on some grouped attribute values include those fields in the field list and write a logical SQL expression that gets the selection. If you are doing it based on a spatial query and get a huge list, perhaps try feeding portions of the OID list in a for loop to the query expression if an error gets thrown or performance drops too drastically.

JacobDrvar

James:

Can you create a feature class with a small subset of features (say 10) and then print out the fidset?

It appears from Richard's last post that the semi-colon delimited string will need to be converted to a comma separated list. You shouldbe able to find python methods to easily perform that process.

print "Data type: " +dsc.dataType
Data type: FeatureLayer
print "File path: " + dsc.path
File path: C:\User\County\Personalworkspace.gdb
print "Catalog path: " + dsc.catalogpath
Catalog path: C:\User\County\Personalworkspace.gdb\Lot_Lines
print "File name: " +dsc.file
File name: Lot_Lines
print "Base name: " + dsc.baseName
Base name: Lot_Lines
print "Name: " + dsc.name
Name: Lot_Lines
print dsc.shapeType
Polyline

Those all work, but when trying to run: print dsc.FidSet, no results are returned. Is that what you were meaning, Michael?

I am now going to work on creating the comma separated list.

JamesSmith7

James:

Can you create a feature class with a small subset of features (say 10) and then print out the fidset?

It appears from Richard's last post that the semi-colon delimited string will need to be converted to a comma separated list. You shouldbe able to find python methods to easily perform that process.

JakeSkinner

Python is case sensitive. Try dsc.fidSet

JamesSmith7

Python is case sensitive. Try dsc.fidSet

The result is the same whether I use dsc.fidSet, dsc.FidSet, or dsc.FIDSet.

JakeSkinner

Attached is some data you can test with. Add the feature class to ArcMap, select a single line, then execute the following:

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 arcLength > 0:
            print arcLength
        else:
            print shapeLength
    del row, rows

Data.zip

RichardFairhurst

The result is the same whether I use dsc.fidSet, dsc.FidSet, or dsc.FIDSet.

Are you positive your layer has a feature selection already applied? If nothing is selected, no FID values should be returned.

JamesSmith7

Attached is some data you can test with. Add the feature class to ArcMap, select a single line, then execute the following:

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 arcLength > 0:
            print arcLength
        else:
            print shapeLength
    del row, rows

Jake, the script works with the feature class you provided, using the Python window within ArcMap.

JamesSmith7

Are you positive your layer has a feature selection already applied? If nothing is selected, no FID values should be returned.

Richard,

I am using the select by rectangle to select one Polyline before running the script.

RichardFairhurst

Jake, the script works with the feature class you provided, using the Python window within ArcMap.

Yes, but it only worked because you selected one feature. If you select 2 features you will get nothing. That is why you have to use the IN operator to work with a list of 0 or more items.

OBJECTID = 12345; 12346

is an invalid selection statement (not sure how Python resolves the list into the SQL statement, but = cannot be used with a list).

OBJECTID IN (12345, 12346)

is valid and will return both records.

OBJECTID IN (12345; 12346)

Returns nothing since a semicolon is invalid in an SQL list.

JakeSkinner

Can you export a small portion of the feature class you are using, zip it, and upload it here?

JamesSmith7

Yes, but it only worked because you selected one feature. If you select 2 features you will get nothing. That is why you have to use the IN operator to work with a list of 0 or more items.

You are correct that the script only works on one record at a time. But, currently that is all I need.

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