New submission from Serhiy Storchaka <storchaka+cpyt...@gmail.com>:
repr() of deeply nested dicts and dictviews can cause a stack overflow.
>>> x = {}
>>> for i in range(100000):
... x = {1: x}
...
>>> repr(x)
Segmentation fault
>>> x = {}
>>> for i in range(100000):
... x = {1: x}
...
>>> repr(x.values())
Segmentation fault
repr() of virtually all other deeply nested collections are guarded by using
Py_EnterRecursiveCall().
>>> x = ()
>>> for i in range(100000):
... x = (x,)
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a
tuple
>>> x = []
>>> for i in range(100000):
... x = [x]
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a
list
>>> x = frozenset()
>>> for i in range(100000):
... x = frozenset({x})
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a
list
>>> from collections import OrderedDict
>>> x = {}
>>> for i in range(100000):
... x = OrderedDict({1: x})
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a
list
>>> from collections import deque
>>> x = deque()
>>> for i in range(100000):
... x = deque([x])
...
>>> repr(x)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
RecursionError: maximum recursion depth exceeded while getting the repr of a
list
But the case of infinite recursion already is handled:
>>> x = {}
>>> x[1] = x
>>> repr(x)
'{1: {...}}'
Only finite but very deep recursion causes a crash.
The one possible solution -- add Py_EnterRecursiveCall() in the implementation
of dict.__repr__(), like it already is added in list.__repr__() and
tuple.__repr__().
The more general solution -- add Py_EnterRecursiveCall() in PyObject_Repr(). In
any case it is called before calling PyObject_Repr() for every item in the repr
of most collections except dict. And it is already added in PyObject_Str().
Therefore adding it will not add much overhead, but can handle more corner
cases.
See also issue18533 and issue25240.
----------
components: Interpreter Core
messages: 306997
nosy: serhiy.storchaka
priority: normal
severity: normal
status: open
title: Stack overflow in repr of deeply nested dicts
type: crash
versions: Python 2.7, Python 3.6, Python 3.7
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue32137>
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