Problem with python script: can only concatenate list (not "str") to list

[JohannesBierer]

I've got a problem with the following script:

import arcpy, os

infile = r"C:\temp4\ALK_Merge.shp"
infileL = "infile_Layer"

count = int(arcpy.GetCount_management(infile).getOutput(0))

x = 99
xC = count/x

xC1 = xC + 2

for i in range(1, xC1):
    print i
    
    sPath = infile.split(".shp")
    
    print sPath
    
    xRange = i * 99
    xRange1 = (i*99)-99
    print xRange
    print xRange1

    outFeature = sPath + "_" + i + ".shp"

    arcpy.MakeFeatureLayer_management (infile, infileL)
    arcpy.SelectLayerByAttribute_management (infileL, "NEW_SELECTION", "\"FID\" <= " + xRange + "AND" + "\"FID\" >= "+ xRange1 + "")
    arcpy.CopyFeatures_management(infileL, outFeature)‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

The problem is in line 25:

outFeature = sPath + "_" + i + ".shp"
TypeError: can only concatenate list (not "str") to list

Any ideas how to solve this?

[XanderBakker]

When yo do sPath = infile.split(".shp") on line 16 he variable sPath will be a list and can't be concatenated with a string. However there are more things going on in your code. I will post an alternative later.

[JohannesBierer]

Because I want to tile the "bigger" shape into "shapes" with exactly 99 features and therefore need to give different names for the output feature class.

[XanderBakker]

try this:

def main():
    import arcpy
    import os
    arcpy.env.overwriteOutput = True

    infile = r"C:\temp4\ALK_Merge.shp"
    infileL = "infile_Layer"

    count = int(arcpy.GetCount_management(infile).getOutput(0))
    x = 99
    xC = count/x
    xC1 = xC + 2

    for i in range(1, xC1):
        print i

        # this will cut off the extension .shp
        fc_pathname = os.path.splitext(infile)[0]

        xRange = i * 99
        xRange1 = (i*99)-99
        print xRange
        print xRange1

        # this will create the file path to the output shapefile
        fc_pathname = "{0}_{1}.shp".format(fc_pathname, i)

        arcpy.MakeFeatureLayer_management (infile, infileL)

        # this will define the where clause
        where = "FID >= {0} AND FID <= {1}".format(xRange1, xRange)
        arcpy.SelectLayerByAttribute_management (infileL, "NEW_SELECTION", where)
        arcpy.CopyFeatures_management(infileL, outFeature)


if __name__ == '__main__':
    main()
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[XanderBakker · Accepted solution]

The method you are using to create the chunks to get exactly 99 features will only work in case there were no deletes in the featureclass.

Take the following example:

def main():
    import arcpy

    fc = r'C:\GeoNet\ArcadeMedellin\ArcadeMedellin.gdb\Solicitudes'
    oids = [r[0] for r in arcpy.da.SearchCursor(fc, ('OID@'))]

    print "FID 99 is at index:", oids.index(99)

    cnt = 0
    for lst in chunks(oids, 99):
        cnt += 1
        print "\nChunk {0} has {1} elements".format(cnt, len(lst))
        print " - OID from {0} to {1}".format(min(lst), max(lst))

def chunks(l, n):
    """Yield successive n-sized chunks from l."""
    for i in range(0, len(l), n):
        yield l[i:i + n]

if __name__ == '__main__':
    main()‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

this will yield:

FID 99 is at index: 92

Chunk 1 has 99 elements
 - OID from 1 to 105

Chunk 2 has 99 elements
 - OID from 106 to 211

Chunk 3 has 36 elements
 - OID from 212 to 250‍‍‍‍‍‍‍‍‍‍

The OID are not continuous, so the chunk function provides a more stable way of creating the appropriate chucks of 99 elements.

[JoshuaBixby]

Not that it will perform any better, I haven't tested, but native slicing and itertools.izip_longest can also be used:

import arcpy
from itertools import izip_longest

chunk_size = #
fc = #

chunk_start = slice(0, None, chunk_size)
chunk_end = slice(chunk_size - 1, None, chunk_size)
with arcpy.da.SearchCursor(fc, "OID@") as cur:
    oids = [oid for oid, in cur]
oid_chunks = izip_longest(oids[chunk_start],
                          oids[chunk_end],
                          fillvalue=oids[-1])
list(oid_chunks)‍‍‍‍‍‍‍‍‍‍‍‍‍‍

[JohannesBierer]

Perfect thank you !

Only a very small thing - it's not

arcpy.CopyFeatures_management(infileL, outFeature)

must be:
arcpy.CopyFeatures_management(infileL,fc_pathname) I think?

[XanderBakker]

Very true. Good catch!

[JoeBorgione]

Isn't the value of i numeric as well?  That seems problematic as well.  While solidly in the rookie phase in my Python carreer, could you join spath into a string, and then concatenate it with i after casting i as a string:

spath = ''.join(infile.split(".shp"))
outfeature = spath+'_'+str(i)+'_ '".shp"
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Untested: 6:00 am at the kitchen table with only one cup of coffee on board....

eta... Never mind:  Looks like Xander slipped in his repsonse while I hacking....

xander_bakker‌