Routines that examine the internals of a CPython dictionary for python 3.3 (modification of Brandon Rhodes' code _dictinfo.py) (See comment at bottom.)

CPython33Dict

"""Routines that examine the internals of a CPython dictionary using python 3.3."""

from ctypes import Structure, c_ulong, POINTER, cast, py_object, CFUNCTYPE, pointer, c_ssize_t, c_void_p
#from math import log

UMAX = 2 ** 32


def cbin(n):
    """Return `n` as a clean 32-bit binary number, without a leading '0b'."""
    if n < 0:
        n = UMAX + n
    return '{0:0>32}'.format(bin(n)[2:])

# Create a singleton with which the dictionary routines below can
# represent null C pointers.


class NULL(object):
    def __repr__(self):
        return 'NULL'

NULL = NULL()

# Create Structures representing the dictionary object and entries, and
# give them useful methods making them easier to use.

class PyDictKeyEntry(Structure):
    """An entry in a dictionary."""
    _fields_ = [
        ('me_hash', c_ulong),
        ('me_key', py_object),
        ('me_value', py_object),
    ]

class PyDictObject(Structure):  # an incomplete type
    """A dictionary object."""
    def __len__(self):
        """Return the number of dictionary entry slots."""
        return self.ma_keys.contents.dk_size

    def slot_of(self, key):
        """Find and return the slot at which `key` is stored."""
        kobj = self.ma_keys.contents             # PyDictKeysObject
        for i in range(len(self)):
            entry = kobj.dk_entries[i]
            try:
                entry.me_key
            except ValueError:
                continue
            k = entry.me_key
            if k is key or (k == key):
                return i
        raise KeyError('cannot find key %r' % (key,))

    def slot_map(self):
        """Return a mapping of keys to their integer slot numbers."""
        m = {}
        kobj = self.ma_keys.contents     # PyDictKeysObject
        for i in range(len(self)): 
            entry = kobj.dk_entries[i]       # an entry
            try:
                entry.me_value
            except:
                continue  # me_value is NULL ptr
            m[entry.me_key] = i
        return m

LOOKUPFUNC = CFUNCTYPE(POINTER(PyDictKeyEntry), POINTER(PyDictObject), py_object, c_ulong, POINTER(POINTER(py_object)))

class PyDictKeysObject(Structure):
    """A key object"""
    _fields_ = [
        ('dk_refcnt', c_ssize_t),
        ('dk_size', c_ssize_t),
        ('dk_lookup', LOOKUPFUNC),
        ('dk_usable', c_ssize_t),
        ('dk_entries', PyDictKeyEntry * 1),
    ]

PyDictKeysObject._dk_entries = PyDictKeysObject.dk_entries
PyDictKeysObject.dk_entries = property(lambda s: cast(s._dk_entries, POINTER(PyDictKeyEntry * s.dk_size))[0])
            
PyDictObject._fields_ = [
        ('ob_refcnt', c_ssize_t),
        ('ob_type', c_void_p),
        ('ma_used', c_ssize_t),
        ('ma_keys', POINTER(PyDictKeysObject)),
        ('ma_values', POINTER(py_object)),  # points to array of ptrs
    ]

def dictobject(d):
    """Return the PyDictObject lying behind the Python dict `d`."""
    if not isinstance(d, dict):
        raise TypeError('cannot create a dictobject from %r' % (d,))
    return cast(id(d), POINTER(PyDictObject)).contents

# Retrieve the secret dummy object used internally by dictionaries to represent a
# previously occupied slot.

def getDummy():
    """get the global dummy object"""
    dummy = None
    d = {0: 0}
    del d[0]
    dummy = dictobject(d).ma_keys.contents.dk_entries[0].me_key
    del d
    return dummy
#

dummy = getDummy()  # <dummy key> of <dummy key> type

def _probe_steps(dummydict, key, final_slot):
    """Find the slots searched to put `key` in `final_slot` of `dummydict`.

    The `dummydict` should be a dictionary in which `key` once resided
    in position `final_slot`, but whose entries have all been deleted,
    leaving dummy entries.  This routine will repeatedly try to insert
    `key` into the dictionary, and each time that it does not land at
    `final_slot` an obstacle is placed where it has landed instead,
    until finally the obstacles make `key` land in the `final_slot`.

    A list of the slots searched is returned.  The last element of this
    list will always be `final_slot`.

    """
    o = dictobject(dummydict)                          # PyDictObject

    # Compute the first slot rather than do an expensive search.
    ko = o.ma_keys.contents                            # PyDictKeysObject
    mask = ko.dk_size - 1
    slot = hash(key) & mask
    slots = [int(slot)]   # since slot often arrives as a long

    # Keep adding obstacles until `key` winds up in `final_slot`.
    while slots[-1] != final_slot:
        if slot == key:  # make sure the integer `slot` is not `key` itself
            slot += len(o)  # don't get why we add this to slot ???
        dummydict[slot] = None  # add the obstacle

        dummydict[key] = None  # add the key
        slot = o.slot_of(key)
        slots.append(slot)
        del dummydict[key]

    # Return the sequence of slots that we searched.
    return slots


def probe_steps(keys, key):
    """Return the search sequence for `key` for a dict built with `keys`.

    `keys` - Dictionary keys, in order of their insertion, including `key`.
    `key` - The key whose collision path we want to explore.
    """
    # Create a dictionary with the given `keys` and figure out at which
    # slot the target `key` wound up.
    d = dict.fromkeys(keys)
    o = dictobject(d)
    final_slot = o.slot_of(key)

    # Empty the dictionary so that it contains only dummy entries, then
    # pass it to the internal _probe_steps() routine.
    for k in list(d):
        del d[k]
    return _probe_steps(d, key, final_slot)


def probe_all_steps(keys):
    """Return the search sequence for each key in a dict built with `keys`.

    `keys` - Dictionary keys, in order of their insertion, including `key`.

    The return value looks like ``{key: [slot, slot, slot], ...}``.

    """
    # Create a dictionary with the given `keys` and find out in which
    # slot each key wound up.
    d = dict.fromkeys(keys)
    o = dictobject(d)
    m = o.slot_map()

    # For each key in the dictionary, find its probe list.
    for key, final_slot in m.items():
        for k in list(d):
            del d[k]  # empty the dictionary
        m[key] = _probe_steps(d, key, final_slot)
    return m

if __name__ == '__main__':

    # Two tiny tests.

    steps = probe_steps([2, 3, 10, 18, 1], 10)
    assert steps == [2, 5]

    stepmap = probe_all_steps([2, 3, 10, 18, 1])
    assert stepmap == {1: [1], 2: [2], 3: [3], 10: [2, 5], 18: [2, 5, 3, 0]}

Need to improve these 2 lines:
PyDictKeysObject._dk_entries = PyDictKeysObject.dk_entries
PyDictKeysObject.dk_entries = property(lambda s: cast(s._dk_entries, POINTER(PyDictKeyEntry * s.dk_size))[0])

since the second line is called each time while iterating through the keys in a dictionary.

The idea is to get the size of dk_entries before casting a pointer to it.