Returns the distance a point is along a line.

getPointDistanceAlongLine.py

#
# @date 06/03/2015
# @author Cindy Williams
#
# Returns the distance a point is along a line. Assumes that the
# existing point and line feature classes have the same spatial reference,
# and the points are snapped to the line.
#
# For use as a standalone script.
#

import arcpy
arcpy.env.workspace = r"C:\Some\Arb\Folder\work.gdb"

# Input variables
fc_line = arcpy.management.MakeFeatureLayer("ftr_line")
fc_pnt = arcpy.management.MakeFeatureLayer("ftr_point")

# Get line geometry - assumes only one feature in feature class
polyline = arcpy.da.SearchCursor(fc_line, "SHAPE@").next()[0]

# Loop over the point feature class
with arcpy.da.SearchCursor(fc_pnt, "SHAPE@") as cursor:
    for row in cursor:
        # Get the percentage the current point is along the line
        perc = polyline.queryPointAndDistance(row[0], True)[1]
        # Calculate the percentage distance in metres
        dist = polyline.getLength()*perc
        print("% along line: {0}%\tDistance along line: {1}m".format(round(perc*100, 2), round(dist, 2)))

print("Script complete.")