TypeError: can't pickle HASH objects?

est electronixtar at gmail.com
Thu Oct 2 12:06:38 CEST 2008


On Oct 2, 5:07 pm, "Gabriel Genellina" <gagsl-... at yahoo.com.ar> wrote:
> En Wed, 01 Oct 2008 16:50:05 -0300, est <electronix... at gmail.com> 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- Hide quoted text -
>
> - Show quoted text -

WOW! I never expected python could be coded like that! Thanks a lot!


On Oct 2, 5:19 pm, "Aaron \"Castironpi\" Brady" <castiro... at gmail.com>
wrote:
> On Oct 2, 4:03 am, est <electronix... at gmail.com> wrote:
>
>
>
>
>
> > On Oct 2, 4:22 pm, "Aaron \"Castironpi\" Brady" <castiro... at gmail.com>
> > wrote:
>
> > > On Oct 2, 2:44 am, est <electronix... at gmail.com> wrote:
>
> > > > On Oct 2, 1:51 pm, "James Mills" <prolo... at shortcircuit.net.au> wrote:
>
> > > > > On Thu, Oct 2, 2008 at 3:34 PM, est <electronix... at gmail.com> wrote:
> > > > > > wow. It's giga-size file. I need stream reading it, md5 it. It may
> > > > > > break for a while.
>
> > > > > So use generators and consume the stream ?
>
> > > > > --JamesMills
>
> > > > > --
> > > > > --
> > > > > -- "Problems are solved by method"
>
> > > > no, I need to serialize half-finished digest, not file stream.
>
> > > > Anyone got solution?
>
> > > I am looking at '_hashopenssl.c'.  If you can find the implementation
> > > of EVP_DigestUpdate, I'll give it a shot to help you write a ctypes
> > > hack to store and write its state.- Hide quoted text -
>
> > > - Show quoted text -
>
> >http://cvs.openssl.org/fileview?f=openssl/crypto/evp/digest.c
>
> > int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *data,
> >              size_t count)
> >         {
> > #ifdef OPENSSL_FIPS
> >         FIPS_selftest_check();
> > #endif
> >         return ctx->digest->update(ctx,data,count);
> >         }
>
> > is this one?
>
> Oops, I needed 'EVP_MD_CTX'.  I went Googling and found it.
>
> http://www.google.com/codesearch?hl=en&q=struct+EVP_MD_CTX+show:mV3VB...
>
> But does Gabriel's work for you?- Hide quoted text -
>
> - Show quoted text -

Still need some hack with py2.5 on linux. Maybe I just need soft link /
usr/lib/python2.4/lib-dynload/md5.so to py2.5 :-)
py2.4 is pre-installed on most of the servers, I think.



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