Add cache to safe_eval

[bch, 2009-12-15 11:47:15]

On 2009/12/15 11:03:54, ced wrote:
> 

OK

[h.goebel, 2009-12-15 16:34:53]

In addition to the review-comment:

I propose putting save_eval into a module by it's own which can easily be held
consistent between client and server. Seeing non-trivial code duplicated within
a project always makes me shiver.

http://codereview.appspot.com/179056/diff/1/2
File tryton/common/common.py (right):

http://codereview.appspot.com/179056/diff/1/2#newcode1188
tryton/common/common.py:1188: if hashlib:
Since you are implementing a cache to gain speed, I suggest removing this
if-statement:

# change import section above like this:
try:
  import hashlib
  MD5 = hashlib.md5
except ImportError:
  import md5
  MD5 = md5.new

#change this if-statement into
key = MD5(source).digest()

Additionally, I see no need for an hexdigest here, so we can use a normals
digest, which cheaper.