Do more imported objects affect performance

[Steven D'Aprano]

On Tue, 02 Dec 2008 11:12:31 +0000, Nick Craig-Wood wrote:

> I prefer the "from module import function".  That means that if "module"
> doesn't supply "function" it raises an exception at compile time, not
> run time when you try to run "module.function".

Wanna bet?


>>> def spam():
...     from math import harmonic_series
...     return harmonic_series()
...
>>> dis.dis(spam)
  2           0 LOAD_CONST               1 (-1)
              3 LOAD_CONST               2 (('harmonic_series',))
              6 IMPORT_NAME              0 (math)
              9 IMPORT_FROM              1 (harmonic_series)
             12 STORE_FAST               0 (harmonic_series)
             15 POP_TOP

  3          16 LOAD_FAST                0 (harmonic_series)
             19 CALL_FUNCTION            0
             22 RETURN_VALUE
>>> spam()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in spam
ImportError: cannot import name harmonic_series


The same thing happens if the from...import is at the top level of the 
module, except that compilation is immediately followed by execution.


> It then becomes very
> easy to see which functions you use from any given module too.

If that's important to you. Personally, I find it more useful to know 
where a function is defined.


-- 
Steven