Flask isn't releasing memory used for large dictionaries

flask_memory_leak.py

import random
import optparse

from flask import redirect, Flask
from memory_profiler import memory_usage

# Create flask app
app = Flask(__name__)
app.debug = True

@app.route('/')
def hello_world():
	###
	# The test:
	# Generate a ~2440 mb dictionary and return a blank page.
	###
	large_dict = {}
	for x in xrange(125000):
		large_row = {}
		for y in xrange(125):
			large_row[random.randint(1, 10000000000)] = random.randint(1, 10000000000)
		large_dict[random.randint(1, 10000000000)] = large_row

	print memory_usage(-1, interval=.2, timeout=1), "end"
	return ''
	###
	# The result:
	# large_dict stays in memory, and memory usage never goes below ~2440 mb
	###

def main():
	app.config['SECRET_KEY'] = "BLAH"
	
	parser = optparse.OptionParser()
	parser.add_option("--host", default="0.0.0.0") # can't use -h, it's already taken by help
	parser.add_option("-p", "--port", default="5123")
	options, args = parser.parse_args()

	if len(args) > 0:
		parser.error("Unexpected arguments: %s" % args)

	app.run(host=options.host, port=int(options.port))

if __name__ == '__main__':
	# Start app
	main()

There's still a reference to the memory, large_dict, when you run the profiler. Even if there wasn't you can't guarantee that the interpreter will have released the memory.

Try running the profiler in the after_request handler, or on a subsequent request. (Provided that the garbage collection has run.)