Creating multipart polyline with Z values

Question

Trying to create multipart polyline from array of arrays (arcpy.Polyline containing multiple arcpy.Array (each is a singlepart line)) or list of coords. Tried it in multiple ways.

Inserting a list of 3D coords into Z-enabled feature class as shown in https://pro.arcgis.com/en/pro-app/latest/arcpy/get-started/writing-geometries.htm class only worked for singlepart features for me.

Creating multipart polyline without Z values also works as also shown in Write Geometries:

This also didn´t work after I added z-coord into the points.

Created multipart polyline without z-coord, inserted it into Z-enabled feature class. Tried to update z-coords using script similar to https://community.esri.com/t5/python-questions/change-z-coordinates-of-vertexes-by-updatecursor/m-p/598505#M46835 but applied to ArcGIS Pro 2.9, the script can run without errors. After I change z-coord of a point, .Z property prints correct z-coord. But after I create a new multipart polyline from points with correct Z-coord and update the row with it, Z-coords of all updated polyline points are equal to 0.

Does anyone know how to solve this?

JohannesLindner · Accepted Answer

Code screenshots are hard to work with, because we can't easily test what you did. To post code as text:

Passing a simple list of coordinate tuples to the InsertCursor seems to be a shortcut that is only valid for singlepart features. Personally, I always create an arcpy.Geometry object and pass that.

test_fc = arcpy.management.CreateFeatureclass("memory", "test_fc", "POLYLINE", has_z="YES", spatial_reference=4326)

coordinates = [
    [-117.2000424, 34.055514, 1],
    [-117.2000788, 34.0592066, 2],
    [-117.1957315, 34.0592309, 5],
    [-117.1956951, 34.0556001, 2],
]

with arcpy.da.InsertCursor(test_fc, ["SHAPE@"]) as cursor:
    points = [arcpy.Point(c[0], c[1], c[2]) for c in coordinates]
    line = arcpy.Polyline(arcpy.Array(points), has_z=True, spatial_reference=4326)
    cursor.insertRow([line])

multipart_coordinates = [
    [coordinates[0], coordinates[1]],
    [coordinates[2], coordinates[3]],
]

with arcpy.da.InsertCursor(test_fc, ["SHAPE@"]) as cursor:
    parts = arcpy.Array([
        arcpy.Array([
            arcpy.Point(p[0], p[1], p[2]) for p in part
        ])
        for part in multipart_coordinates])
    line = arcpy.Polyline(parts, has_z=True, spatial_reference=4326)
    cursor.insertRow([line])