Uses an arcpy FeatureSet to allow the user to interactively create points on a line which will be used to split that line into parts, while retaining all attributes.

splitLineAtInteractivePoint.py

'''
@date 06/10/2015
@author Cindy Williams
@version 1.0

Uses an arcpy FeatureSet to allow the user to interactively create
points on a line which will be used to split that line into parts,
while retaining all attributes.

Requirements:
- Works as a script tool. Add to a toolbox.
- Can only work on a single line for now. Select the line, right
  click the layer and "Create layer from selected features". Use
  this selection layer as input to the tool.
- Digitise points snapped to the selected line. Tool will fail if not
  snapped
- Digitise points left to right along the line.

Future versions will include:
- split multiple lines at same time
- snap points automatically/error that points should be snapped
- points will be sorted after digitising to ensure correct order

Built on an idea here http://gis.stackexchange.com/questions/154708/standalone-python-script-to-split-a-polyline-with-a-point-layer
'''

import arcpy

inset = arcpy.GetParameter(0) # FeatureSet of interactive points from ArcMap
inline = arcpy.GetParameterAsText(1) # Input polyline feature layer

# Get all field names excluding dynamic fields
fields = ["SHAPE@"]
fields.extend([field.name for field in arcpy.ListFields(inline) if field.name not in ["OBJECTID", "Shape_Length", "Shape"]])

# Open an insert cursor for inserting the cut lines
cursor_ins = arcpy.da.InsertCursor(inline, fields)

# Get the spatial reference from the polyline
sr = arcpy.Describe(inline).spatialReference

# Get the polyline and delete the original record
with arcpy.da.UpdateCursor(inline, fields) as cursor:
    for row in cursor:
        polyline = row
        cursor.deleteRow()

# Iterate over the points
with arcpy.da.SearchCursor(inset, "SHAPE@") as cursor:
    for row in cursor:
        point = row[0].firstPoint
        # Build a temporary diagonal line from the point
        diag = arcpy.Polyline(arcpy.Array([arcpy.Point(point.X + 10.0, point.Y + 10.0), arcpy.Point(point.X-10.0, point.Y-10.0)]), sr)
        # Cut the original polyline
        geom = polyline[0].cut(diag)
        
        # Create a new line with the right side of the geom i.e. finished with this side
        newline = [geom[1]]
        newline.extend(polyline[1:])
        
        # Insert the line into the feature layer
        cursor_ins.insertRow(newline)

        # Set the left side of the cut line as the new line for cutting
        polyline = [geom[0]]
        polyline.extend(newline[1:])

# Insert the last portion of the line
cursor_ins.insertRow(polyline)

del cursor_ins
del polyline