"""Test for memory leak in CPython 3.6b1

Popping an attribute off of `self.__dict__` causes unbounded memory growth.

It only takes about a dozen iterations to use up several GB of memory.
"""
from contextlib import contextmanager
import time

class Test(object):

    def __init__(self):
        # Critical part 1:
        # calling this in `__init__` causes later calls to result in unbounded memory growth
        # even across instances.
        # If not called in `__init__`, counter resets for each instance,
        # but bug remains.
        self.__dict__ = {}
        self.trigger_bug()
    
    def trigger_bug(self):
        """Set an attribute and then remove it from self.__dict__"""
        # Critical part 2:
        # This dict.pop is more expensive each time it is called.
        # The cost does not reset per Test instance, it grows continuously.
        print(len(self.__dict__))
        self.attr = 1
        self.__dict__.pop('attr', None)


@contextmanager
def timer():
    tic = time.monotonic()
    try:
        yield
    finally:
        dt = time.monotonic() - tic
        print('%g' % dt)

print("Reusing Test instance")
obj = Test()
for i in range(100):
    print('\n%i' % i, end=' ')
    with timer():
        obj.trigger_bug()

# the problem accrues even across instances
print("New test instance each time")
for i in range(200):
    print('\n%i' % i, end=' ')
    with timer():
        obj = Test()
        obj.trigger_bug()