Graham Dumpleton commented on MODPYTHON-93:

Okay, bit the bullet and made FieldStorage a bit more dictionary like after a 
bit of discussion on the mailing lists by adding __setitem__(), __delitem__(), 
__iter__(), __repr__() and clear() on top of other dictionary like methods it 
already had. To say it is dictionary like is probably only true though for the 
case where there is a single value against all form fields. Once you start 
having multiple values against a form field it starts to behave a bit 
differently. That it isn't strictly the same has been documented.

First difference is that subscript operator when used to access fields returns 
the actual value when there is only one, but a list of values when there is 
more than one. To always ensure one only gets a single value, should use 
getfirst(), if always a list, use getlist() instead. The way the subscript 
operator behaves is the same as cgi.FieldStorage so not doing anything 
different here.

Second difference is that subscript operator when used to set the value of a 
field actually adds the value to an existing value if one already exists. In 
other words, it does not replace the existing value but adds another. This is 
because it uses add_field(). There is no equivalent in cgi.FieldStorage, but 
this behaviour is consistent with how Trac was overriding the class and 
providing its own __setitem__() method. If one really wants to supplant an 
existing value, should use del operator first to remove existing values.

So there is some strangeness in how it works. If anyone specifically sees a big 
problem with the __setitem__() method and how it works, speak up.

> 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: Graham Dumpleton
>            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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