find_recursionlimit.py

#! /usr/bin/env python
"""Find the maximum recursion limit that prevents interpreter termination.

This script finds the maximum safe recursion limit on a particular
platform. If you need to change the recursion limit on your system,
this script will tell you a safe upper bound. To use the new limit,
call sys.setrecursionlimit().

This module implements several ways to create infinite recursion in
Python. Different implementations end up pushing different numbers of
C stack frames, depending on how many calls through Python's abstract
C API occur.

After each round of tests, it prints a message:
"Limit of NNNN is fine".

The highest printed value of "NNNN" is therefore the highest potentially
safe limit for your system (which depends on the OS, architecture, but also
the compilation flags). Please note that it is practically impossible to
test all possible recursion paths in the interpreter, so the results of
this test should not be trusted blindly -- although they give a good hint
of which values are reasonable.

NOTE: When the C stack space allocated by your system is exceeded due
to excessive recursion, exact behaviour depends on the platform, although
the interpreter will always fail in a likely brutal way: either a
segmentation fault, a MemoryError, or just a silent abort.

NB: A program that does not use __methods__ can set a higher limit.
"""

importsys
importitertools

classRecursiveBlowup1:
def__init__(self):
self.__init__()

deftest_init():
returnRecursiveBlowup1()

classRecursiveBlowup2:
def__repr__(self):
returnrepr(self)

deftest_repr():
returnrepr(RecursiveBlowup2())

classRecursiveBlowup4:
def__add__(self, x):
returnx+self

deftest_add():
returnRecursiveBlowup4() +RecursiveBlowup4()

classRecursiveBlowup5:
def__getattr__(self, attr):
returngetattr(self, attr)

deftest_getattr():
returnRecursiveBlowup5().attr

classRecursiveBlowup6:
def__getitem__(self, item):
returnself[item-2] +self[item-1]

deftest_getitem():
returnRecursiveBlowup6()[5]

deftest_recurse():
returntest_recurse()

deftest_cpickle(_cache={}):
try:
importcPickle
exceptImportError:
print"cannot import cPickle, skipped!"
return
l=None
forninitertools.count():
try:
l=_cache[n]
continue# Already tried and it works, let's save some time
exceptKeyError:
foriinrange(100):
l= [l]
cPickle.dumps(l, protocol=-1)
_cache[n] =l

defcheck_limit(n, test_func_name):
sys.setrecursionlimit(n)
iftest_func_name.startswith("test_"):
printtest_func_name[5:]
else:
printtest_func_name
test_func=globals()[test_func_name]
try:
test_func()
# AttributeError can be raised because of the way e.g. PyDict_GetItem()
# silences all exceptions and returns NULL, which is usually interpreted
# as "missing attribute".
except (RuntimeError, AttributeError):
pass
else:
print"Yikes!"

limit=1000
while1:
check_limit(limit, "test_recurse")
check_limit(limit, "test_add")
check_limit(limit, "test_repr")
check_limit(limit, "test_init")
check_limit(limit, "test_getattr")
check_limit(limit, "test_getitem")
check_limit(limit, "test_cpickle")
print"Limit of %d is fine"%limit
limit=limit+100