Python NewCellIterator leak

Expected Behavior

iterating cell using polydataInstance.NewCellIterator() multiple times should increase the memory usage linearly

Current Behavior

the iterator seams to retain the allocated memory even when the python wrapper goes out of scope

Possible Solution

The wrapper destructor should deallocate the wrapped memory

Steps to Reproduce

import urllib
import os
import psutil
import vtk
import time

# download sample data
if not os.path.exists("./42400-IDGH.stl"):
    open("./42400-IDGH.stl", "wb").write(
        urllib.urlopen("https://github.com/naucoin/VTKData/raw/master/Data/42400-IDGH.stl").read())


def iterateOverCells(dataset):
    iterator = dataset.NewCellIterator()
    while not iterator.IsDoneWithTraversal():
        iterator.GoToNextCell()


def iterateOverCellsInefficient(dataset):
    for i in range(dataset.GetNumberOfCells()):
        dataset.GetCell(i)


reader = vtk.vtkSTLReader()
reader.SetFileName("./42400-IDGH.stl")
reader.Update()

process = psutil.Process(os.getpid())

efficient = []
inefficient = []

start = time.time()
for i in xrange(1000):
    inefficient.append(process.memory_info().rss)
    iterateOverCellsInefficient(reader.GetOutput())

print time.time() - start

start = time.time()
for i in xrange(1000):
    efficient.append(process.memory_info().rss)
    iterateOverCells(reader.GetOutput())

print time.time() - start

import matplotlib as mpl

mpl.use("Agg")
from matplotlib import pyplot as plt

toMB = lambda d: d / 1024. / 1024.
plt.plot(map(toMB, inefficient), label="inefficient")
plt.plot(map(toMB, efficient), label="efficient")
plt.legend()
plt.title("memory usage (MB)")
plt.show()
plt.savefig("memory.png")

Context (Environment)

Python 2.7.15 (default, Jan 12 2019, 22:20:12) 
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)] on darwin

backports.functools-lru-cache==1.5
cycler==0.10.0
kiwisolver==1.0.1
matplotlib==2.2.4
numpy==1.16.2
psutil==5.6.1
pyparsing==2.3.1
python-dateutil==2.8.0
pytz==2018.9
six==1.12.0
subprocess32==3.5.3
vtk==8.1.2