h(re) for help, import re - on NameError

[Veek M]

Chris Angelico wrote:

> On Thu, Sep 22, 2016 at 8:10 PM, Veek M <vek.m1234 at gmail.com> wrote:
>> Is there a way to use .pythonrc.py to provide a help function that
>> autoloads whatever module name is passed like so:
>> \>>> h(re)
>>
>> I tried inheriting site._Helper and overriding __init__ and __call__
>> but that didn't work, also I don't know how to deal/trap/catch the
>> NameError (no quotes on h(re)) - is there a way to insert a
>> try/except block around the >>> prompt?
>>
>> I hate having to: import whatever every-time i forget. Actually could
>> I ditch the () in h(re) and just do: h re - the joy of that :p
> 
> You could use sys.excepthook to catch the NameError. I don't know of a
> way to catch the SyntaxError and look at the original text, but with
> NameError it's pretty easy:
> 
> def excepthook(t,v,tb):
>     if t is NameError:
>         n = v.args[0].split("'")[1]
>         globals()[n] = __import__(n)
>         exec(tb.tb_frame.f_code, tb.tb_frame.f_globals)
>     else:
>         excepthook.old(t,v,tb)
> 
> import sys
> excepthook.old = sys.excepthook
> sys.excepthook = excepthook
> 
> Paste that into interactive Python and give it a try. Be aware that
> it'll attempt to import *any* dud name, so it'll potentially slow
> stuff down any time you typo. Also, it re-executes the current
> traceback frame, which may or may not be appropriate; it's fine for
> help(re), but not otherwise.
> 
> As an alternative, you could inspect tb.tb_frame.f_code to see if it
> matches "help(x)", and if it does, simply re-execute it with the
> string form of the name:
> 
> exec(tb.tb_frame.f_code, tb.tb_frame.f_globals, {n: n})
> 
> This works because help('re') does the same thing as help(re), so by
> effectively setting re="re", you gain that functionality without
> actually importing into the global namespace.
> 
> Adequately recognizing help(re) without false positives is left as an
> exercise for the reader. :)
> 
> ChrisA

works great :) - okay so you save and replace the default exception 
handler for the interpreter. Then when the procedure is called, check to 
see if type is NameError - if yes, then value contains the error string 
with module name, so you split and extract module name, and import the 
module and map it to a name in the global NS and hey presto (run the old 
code with the modified NS - that's a bit funky)!

Regarding fiddling with the code-object, yep, 
tb.tb_frame.f_code.co_names has a tuple ('h', 're') I suppose that's 
clean because it's your input after all vs splitting on something system 
generated (like an error message) 

works brilliantly - thanks :)