[IPython-user] cannot paste indented code

[Fernando Perez]

Matt Wilkie wrote:
>>Just add an 'if 1:' at the first line, and paste away, even if the code is
>>indented multiple levels (the above was a chunk twice-indented in an emacs
>>buffer).
> 
> 
> thanks for that! This is very quick and easy and, for me, negates the
> desire for more magic on top of what is already a growing pile. :)

And notice how the 'if 1' is optimized away at the bytecode level, so you 
don't even lose precious performance :)

In [9]: print src

if 1:
     x = 1


In [10]: dis.dis(compile(src,'<>','single'))
   2           0 JUMP_FORWARD             4 (to 7)
               3 JUMP_IF_FALSE           10 (to 16)
               6 POP_TOP

   3     >>    7 LOAD_CONST               0 (1)
              10 STORE_NAME               0 (x)
              13 JUMP_FORWARD             1 (to 17)
         >>   16 POP_TOP
         >>   17 LOAD_CONST               1 (None)
              20 RETURN_VALUE

In contrast, 'if True' is NOT optimized away:

In [11]: dis.dis(compile(src.replace('if 1','if True'),'<>','single'))
   2           0 LOAD_NAME                0 (True)
               3 JUMP_IF_FALSE           10 (to 16)
               6 POP_TOP

   3           7 LOAD_CONST               0 (1)
              10 STORE_NAME               1 (x)
              13 JUMP_FORWARD             1 (to 17)
         >>   16 POP_TOP
         >>   17 LOAD_CONST               1 (None)
              20 RETURN_VALUE


Cheers,

f