dynamically modify help text

[Benjamin Kaplan]

On Mon, Jun 28, 2010 at 11:25 AM, Chris Rebert <clp2 at rebertia.com> wrote:
> On Mon, Jun 28, 2010 at 11:13 AM, Brian Blais <bblais at bryant.edu> wrote:
>> On Jun 27, 2010, at 22:37 , Red Forks wrote:
>>> Read you doc file and set the __doc__ attr of the object you want to
>>> change.
>>>
>>> On Monday, June 28, 2010, Brian Blais <bblais at bryant.edu> wrote:
>>>> I know that the help text for an object will give a description of every
>>>> method based on the doc string.  Is there a way to add something to this
>>>> text, specific to an object, but generated at run-time?  I have an object
>>>> that reads a file, and I would like part of that file to be shown if one
>>>> does:  help(myobject)
>>
>> python file:
>>
>> #=============
>> class A(object):
>>    pass
>>
>> help_text="this is some text"
>>
>> a=A()
>> a.__doc__=help_text
>> #=============
>>
>> in ipython:
>>
>> shows up here:
>>
>> In [5]:a?
>> Type:           A
>> Base Class:     <class '__main__.A'>
>> String Form:    <__main__.A object at 0x13270f0>
>> Namespace:      Interactive
>> File:
>> /Library/Frameworks/Python.framework/Versions/5.0.0/lib/python2.5/site-packages/IPython/FakeModule.py
>> Docstring:
>>    this is some text
>>
>>
>> but not with the help command:
>>
>> In [6]:help(a)
>> Help on A in module __main__ object:
>>
>> class A(__builtin__.object)
>>  |  Data descriptors defined here:
>>  |
>>  |  __dict__
>>  |      dictionary for instance variables (if defined)
>>  |
>>  |  __weakref__
>>  |      list of weak references to the object (if defined)
>>
>>
>> also does the same thing with the regular python prompt.
>>
>> is there a reason for this?
>
> __doc__ is normally defined on classes, e.g. `A`, not instances, e.g.
> `a`. help() looks for __doc__ accordingly.
>
> Cheers,
> Chris
> --


Just to save the OP some trouble later on: this optimization is done
for most of the __*__ methods. Overriding __add__ on an instance won't
change the behavior of a + b.