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      1 #! /usr/bin/env python
      2 """Find the maximum recursion limit that prevents interpreter termination.
      3 
      4 This script finds the maximum safe recursion limit on a particular
      5 platform.  If you need to change the recursion limit on your system,
      6 this script will tell you a safe upper bound.  To use the new limit,
      7 call sys.setrecursionlimit().
      8 
      9 This module implements several ways to create infinite recursion in
     10 Python.  Different implementations end up pushing different numbers of
     11 C stack frames, depending on how many calls through Python's abstract
     12 C API occur.
     13 
     14 After each round of tests, it prints a message:
     15 "Limit of NNNN is fine".
     16 
     17 The highest printed value of "NNNN" is therefore the highest potentially
     18 safe limit for your system (which depends on the OS, architecture, but also
     19 the compilation flags). Please note that it is practically impossible to
     20 test all possible recursion paths in the interpreter, so the results of
     21 this test should not be trusted blindly -- although they give a good hint
     22 of which values are reasonable.
     23 
     24 NOTE: When the C stack space allocated by your system is exceeded due
     25 to excessive recursion, exact behaviour depends on the platform, although
     26 the interpreter will always fail in a likely brutal way: either a
     27 segmentation fault, a MemoryError, or just a silent abort.
     28 
     29 NB: A program that does not use __methods__ can set a higher limit.
     30 """
     31 
     32 import sys
     33 import itertools
     34 
     35 class RecursiveBlowup1:
     36     def __init__(self):
     37         self.__init__()
     38 
     39 def test_init():
     40     return RecursiveBlowup1()
     41 
     42 class RecursiveBlowup2:
     43     def __repr__(self):
     44         return repr(self)
     45 
     46 def test_repr():
     47     return repr(RecursiveBlowup2())
     48 
     49 class RecursiveBlowup4:
     50     def __add__(self, x):
     51         return x + self
     52 
     53 def test_add():
     54     return RecursiveBlowup4() + RecursiveBlowup4()
     55 
     56 class RecursiveBlowup5:
     57     def __getattr__(self, attr):
     58         return getattr(self, attr)
     59 
     60 def test_getattr():
     61     return RecursiveBlowup5().attr
     62 
     63 class RecursiveBlowup6:
     64     def __getitem__(self, item):
     65         return self[item - 2] + self[item - 1]
     66 
     67 def test_getitem():
     68     return RecursiveBlowup6()[5]
     69 
     70 def test_recurse():
     71     return test_recurse()
     72 
     73 def test_cpickle(_cache={}):
     74     try:
     75         import cPickle
     76     except ImportError:
     77         print "cannot import cPickle, skipped!"
     78         return
     79     l = None
     80     for n in itertools.count():
     81         try:
     82             l = _cache[n]
     83             continue  # Already tried and it works, let's save some time
     84         except KeyError:
     85             for i in range(100):
     86                 l = [l]
     87         cPickle.dumps(l, protocol=-1)
     88         _cache[n] = l
     89 
     90 def check_limit(n, test_func_name):
     91     sys.setrecursionlimit(n)
     92     if test_func_name.startswith("test_"):
     93         print test_func_name[5:]
     94     else:
     95         print test_func_name
     96     test_func = globals()[test_func_name]
     97     try:
     98         test_func()
     99     # AttributeError can be raised because of the way e.g. PyDict_GetItem()
    100     # silences all exceptions and returns NULL, which is usually interpreted
    101     # as "missing attribute".
    102     except (RuntimeError, AttributeError):
    103         pass
    104     else:
    105         print "Yikes!"
    106 
    107 limit = 1000
    108 while 1:
    109     check_limit(limit, "test_recurse")
    110     check_limit(limit, "test_add")
    111     check_limit(limit, "test_repr")
    112     check_limit(limit, "test_init")
    113     check_limit(limit, "test_getattr")
    114     check_limit(limit, "test_getitem")
    115     check_limit(limit, "test_cpickle")
    116     print "Limit of %d is fine" % limit
    117     limit = limit + 100
    118