use import *

[Chris Angelico]

On Tue, Aug 2, 2016 at 1:31 AM, Ganesh Pal <ganesh1pal at gmail.com> wrote:
> I am a Linux user on python 2,6 . I have a very simple question
>
> I was going the zen of python by Tim peters and found an example  that
> demonstrates Explicit is better than implicit
>
> """Load the cat, dog, and mouse models so we can edit instances of them."""
> def load():
>     from menagerie.cat.models import *
>     from menagerie.dog.models import *
>     from menagerie.mouse.models import *
> #-----------------------------------------------------------------------
> def load():
>     from menagerie.models import cat as cat_models
>     from menagerie.models import dog as dog_models
>     from menagerie.models import mouse as mouse_models
> #-----------------------------------------------------------------------
> print 'Explicit is better than implicit.'
>
>
> I had a question on the above example
>
> 1. I haven't used " from menagerie.cat.models import *  is it a good
> programming practice to use  import * ?   if answer is "NO " then  are
> there situation where you are forced to use import *
>

Specifically to that example? No it's never a good idea to do a
star-import inside a function. It's completely illegal in Python 3.
Normally, you'll want to do your imports at module level, and not with
the star.

There are a very few places where a star import is the best thing to
do, and they're usually because of a tight binding between the two
modules. For example, it's common for __init__.py to say "from
.something import *", to make a package's module's contents available
in the package itself. Also, a Python module with a C accelerator will
often start or end by star-importing from the accelerator (eg ast.py
"from _ast import *"). If you're not doing something like that, there
are only a handful of modules that are really designed with
star-imports in mind (eg tkinter, stat), and even then, I personally
don't recommend it.

The downside of a star-import is that it breaks the common pattern
that the first use of a name is its definition. If you see, somewhere
in a program, "conn = psycopg2.connect(...)", you can go up to the top
of the program to find "import psycopg2" and know that it's a module -
even if you don't recognize the name (since it's a third-party one),
you can know that it's a module. Similarly, if you see "conn =
connect(...)", you can go up to the top - but then it depends on
whether the program author wrote "from psycopg2 import connect" or
"from psycopg2 import *". In the latter case, you have to *guess* that
the name "connect" might have come from there.

So, my recommendation is: Use "import *" only when you control both
ends of something. Otherwise, be explicit.

ChrisA