[IPython-User] question about extensions

[MinRK]

On Wed, Oct 17, 2012 at 11:38 AM, Michael Kuhlen <kuhlen@gmail.com> wrote:

> Hi there
>
> A question about IPython extensions. From reading the documentation it
> looks like extension are meant to modify the behaviour of the shell,
> and so my question might not make any sense, but let me ask anyway. Is
> there some way to use extensions inside an externally defined
> function?
>
> More specifically, I've been using the ipython-physics
> (https://bitbucket.org/birkenfeld/ipython-physics) extension to handle
> physical quantities with units. This works great in the IPython shell
> and in notebooks, but it doesn't seem to work when I try to use it
> inside externally defined functions. Here's what I mean:
>
> In [1]: %load_ext physics
> Unit calculation and physics extensions activated.
>
> In [2]: print Q('1 hplanck').base
> 6.6260696e-34 m^2*kg/s
>
> In [3]: def test():
>    ...:     print Q('1 hplanck').base
>    ...:
>
> In [4]: test()
> 6.6260696e-34 m^2*kg/s
>
> In [5]: !cat test.py
> def test():
>     print Q('1 hplanck').base
>
> In [6]: import test as t
>
> In [7]: t.test()
> ---------------------------------------------------------------------------
> NameError                                 Traceback (most recent call last)
> <ipython-input-6-f69a6e70fa4a> in <module>()
> ----> 1 t.test()
>
> /home/mqk/test.py in test()
>       1 def test():
> ----> 2     print Q('1 hplanck').base
>
> NameError: global name 'Q' is not defined
>
>
>
> Perhaps this is unavoidable, but I'd love to find a way to use
> physical quantities also inside externally defined functions.
>

extensions are just modules on a special path.  They do not (generally)
affect anything other than the user namespace and IPython itself.

To get a name from an extension, you treat it just like any other module
(at least after it has been loaded):

# load the extension first, so that the 'physics' module exists
%load_ext physics

# then its names become importable:
from physics import Q

-MinRK


> Any insights?
>
> Thanks,
>
> Mike
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