[jira] Resolved: (MODPYTHON-93) Improve util.FieldStorage efficiency

["Graham Dumpleton (JIRA)" <ji...@apache.org>]

     [ http://issues.apache.org/jira/browse/MODPYTHON-93?page=all ]

Graham Dumpleton resolved MODPYTHON-93.
---------------------------------------

    Resolution: Fixed

I have looked at the code for this again and to somehow accommodate older versions of Trac is only going to introduce horrible little hacks in mod_python that we don't need, so it just isn't worth the trouble to try and support the older versions. People will simply need to upgrade to at least Trac 0.10.0 if they want to use mod_python 3.3.

If the hacks were done, there would be two parts to it. The first is that Trac derives from util.FieldStorage and adds a __setitem__() method. This would need to be overridden from the base class by replacing it with add_field(). 

  def __init__(self, ...):
    ...
    self.__setitem__ = self.add_field

It has to be done in the constructor and not just as a method, as doing it as a method means derived class overrides it. At that point in the constructor, derived class one is in place and so we effectively replace it.

The second part would be more difficult and why it isn't worth the trouble. The problem here is that although the derived class adds __setitem__(), it doesn't itself use it in the derived class constructor. Instead, it does the nasty thing of accessing the base class 'list' attribute directly, thereby duplicating the same code as in __setitem__() that we need to replace. The only way around this nastiness would be for the base class to override the 'append()' method of the 'list' attribute itself and do extra special magic to check for arguments of the old style and change things on the fly, updating the associated index attribute as well. This is just all too messy and magic and would surely come back and bite us.

In summary, not worth the trouble. Trac people will just have to upgrade.



> Improve util.FieldStorage efficiency
> ------------------------------------
>
>                 Key: MODPYTHON-93
>                 URL: http://issues.apache.org/jira/browse/MODPYTHON-93
>             Project: mod_python
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 3.2.7
>            Reporter: Jim Gallacher
>         Assigned To: Jim Gallacher
>            Priority: Minor
>             Fix For: 3.3
>
>         Attachments: modpython325_util_py_dict.patch
>
>
> Form fields are saved as a list in a FieldStorage class instance. The class implements a __getitem__ method to provide dict-like behaviour.  This method iterates over the complete list for every call to __getitem__. Applications that need to access all the fields when processing the form will show O(n^2) behaviour where n == the number of form fields. This overhead could be avoided by creating a dict (to use as an index) when the FieldStorage instance is created.
> Mike Looijmans has been investigating StringField and Field as well. It is probably reasonable to include information on his work in this issue as well, so that we can consider all of these efficiency issues in toto.

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