import arcpy
arcpy.env.workspace = r"C:UsersAlizaDesktopGIS Programming FundamentalsFinal_ProjectContours"
arcpy.CheckOutExtension("3D")
out_tin = "SampleTinssas"
height_field = "Elevation"
in_features = r"C:UsersAlizaDesktopGIS Programming FundamentalsFinal_ProjectContoursSite_37_Contours.shp"
sr = arcpy.Describe(in_features).spatialReference
arcpy.CreateTin_3d(out_tin, sr, "Site_37_Contours.shp", "DELAUNAY")

arcpy.CheckInExtension("3D")

"C:Program FilesArcGISProbinPythonenvsarcgispro-py3python.exe"
C:/Users/Aliza/PycharmProjects/finaltest.py
Traceback (most recent call last):
 File "C:/Users/Aliza/PycharmProjects/finaltest.py", line 8, in <module>
    arcpy.CreateTin_3d(out_tin, sr, "Site_37_Contours.shp", "DELAUNAY")
  File "C:Program FilesArcGISProResourcesArcPyarcpyddd.py", line
 2922, in CreateTin
    raise e
  File "C:Program FilesArcGISProResourcesArcPyarcpyddd.py", line
2919, in CreateTin
    retval =
convertArcObjectToPythonObject(gp.CreateTin_3d(*gp_fixargs((out_tin,
spatial_reference, in_features, constrained_delaunay), True)))
  File "C:Program
FilesArcGISProResourcesArcPyarcpygeoprocessing_base.py", line 506, in
<lambda>
   return lambda *args: val(*gp_fixargs(args, True))
arcgisscripting.ExecuteError: ERROR 999999: Error executing function.
Failed to execute (CreateTin).