En Wed, 01 Oct 2008 16:50:05 -0300, est <[EMAIL PROTECTED]> escribió:
import md5
a=md5.md5()
import pickle
pickle.dumps(a)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Python25\lib\pickle.py", line 1366, in dumps
Pickler(file, protocol).dump(obj)
File "C:\Python25\lib\pickle.py", line 224, in dump
self.save(obj)
File "C:\Python25\lib\pickle.py", line 306, in save
rv = reduce(self.proto)
File "C:\Python25\lib\copy_reg.py", line 69, in _reduce_ex
raise TypeError, "can't pickle %s objects" % base.__name__
TypeError: can't pickle HASH objects
Why can't I pickle a md5 object? Is it because md5 algorithm needs to
read 512-bits at a time?
I need to md5() some stream, pause(python.exe quits), and resume
later. It seems that the md5 and hashlib in std module could not be
serialized?
Yep, they're implemented in C and have no provision for serializing.
If you can use the old _md5 module, it is far simpler to serialize; a
md5object just contains a small struct with 6 integers and 64 chars, no
pointers.
With some help from ctypes (and a lot of black magic!) one can extract the
desired state, and restore it afterwards:
--- begin code ---
import _md5
import ctypes
assert _md5.MD5Type.__basicsize__==96
def get_md5_state(m):
if type(m) is not _md5.MD5Type:
raise TypeError, 'not a _md5.MD5Type instance'
return ctypes.string_at(id(m)+8, 88)
def set_md5_state(m, state):
if type(m) is not _md5.MD5Type:
raise TypeError, 'not a _md5.MD5Type instance'
if not isinstance(state,str):
raise TypeError, 'state must be str'
if len(state)!=88:
raise ValueError, 'len(state) must be 88'
a88 = ctypes.c_char*88
pstate = a88(*list(state))
ctypes.memmove(id(m)+8, ctypes.byref(pstate), 88)
--- end code ---
py> m1 = _md5.new()
py> m1.update("this is a ")
py> s = get_md5_state(m1)
py> del m1
py>
py> m2 = _md5.new()
py> set_md5_state(m2, s)
py> m2.update("short test")
py> print m2.hexdigest()
95ad1986e9a9f19615cea00b7a44b912
py> print _md5.new("this is a short test").hexdigest()
95ad1986e9a9f19615cea00b7a44b912
The code above was only tested with Python 2.5.2 on Windows, not more than
you can see. It might or might not work with other versions or platforms.
It may even create a (small) black hole and eat your whole town. Use at
your own risk.
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
