[IPython-dev] cell magics

Thomas Kluyver takowl@gmail....
Sat Feb 16 16:39:42 CST 2013


That's quite a lot to read, but while I think about it in more detail, a
couple of bits that jump out at me:

On 16 February 2013 22:07, Jason Grout <jason-sage@creativetrax.com> wrote:

> %time some_function
>
> now I want to add a few more things to the time run.  All I have to do
> is change where the string is:
>
> %time
> some_function
> some_other function
>
> and the lack of a string after %time tells me that I should look below
> %time for the string.  I don't have to constantly keep adjusting the %
> character(s).
>

For %%timeit, however, we use the remainder of the line as a setup
statement, before timing the body. Now you can argue that that's a bad
idea, but it's useful to have that distinction.


> P.S. Actually, after thinking about it more, since a single % is
> ambiguous syntax, I think I would prefer all string decorators be
> invoked with %%, which is invalid python syntax.  Then we won't have
> this problem:
>
> cd=5
> a=4\
> %cd
>
> or this problem:
>
> cd=4
> a="time: %d"\
> %cd
>

My input transformation work should handle such cases. Arguably it could be
done more easily if we used a syntax like %% that could never appear in a
valid Python statement, but it still wouldn't be trivial:

a = """
%%foo
"""

> ...

>  I think it's pretty clear which statement is more readable.  This focus
> on readability over brevity (remember, "Readability counts") is part of
> why python is so good in general.
>

And part of the reason IPython exists is to provide for the cases when you
do want brevity. Because there are times when you want to type '%run -d
foo' than 'pdb.runcall(execfile, "foo.py")'.

Of course, IPython has evolved - when it was only a shell, most of what you
entered was just for single use, so readability wasn't hugely important.
When you're writing & publishing a notebook, readability is a much bigger
deal. But I've yet to see a particular problem with people abusing magic
syntax and making notebooks hard to read.

> * backwards compatibility (with IPP and previous IPython versions, as
> well as IDL and matlab apparently?).  But I'll point out that we can
> easily support this too, in almost exactly the same invocation:
>
> %timeit('-r 5 -and -other -options') 2+3

Honestly, I wouldn't call that 'almost the same invocation'. Moreover, it
sacrifices the brevity without enforcing any corresponding gain in
readability.

Thomas
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