Confused about namespaces

[Alex Martelli]

Re: Confused about namespaces

KvS <keesvanschaik@ gmail.com> wrote:
[color=blue][color=green]
> > There's no reason not to just "import wx" if you want that.[/color]
>
> Yes, that's clear. But if you would make some huge application that has
> a large number of nested modules, each importing the former one, then
> avoiding the use of "from ... import *" would mean that you have to use
> long references like foo1.foo2.... to get to the lowest modules plus[/color]

Not at all -- you may perfectly well "import a.b.c.d as e" and use e as
the reference throughout the importing module.

But the point is, modules should be MODULAR (duh) -- if I 'import x' I
should NOT rely on what x itself imports (and so on transitively), just
on what x ``exports'', so to speak, at its TOP level. The Law of
Demeter in its simplified form "if you have more than one dot in your
reference you're doing things wrong" applies. In fact, the many-dots
form of module naming is intended for nested PACKAGES, *NOT* for
"modules which import each other".
[color=blue]
> that you'd have to check each module for imports outside this tree.[/color]

Why would you have to check any module for such "outside imports"? I
don't see the need for any checks.


If you just simply forget the very _existence_ of "from X import *",
your Python code can only grow better as a result. I earnestly hope it
disappears come Python 3.0 time...


Alex

[Alex Martelli]

Re: Confused about namespaces

KvS <keesvanschaik@ gmail.com> wrote:
[color=blue][color=green]
> > There's no reason not to just "import wx" if you want that.[/color]
>
> Yes, that's clear. But if you would make some huge application that has
> a large number of nested modules, each importing the former one, then
> avoiding the use of "from ... import *" would mean that you have to use
> long references like foo1.foo2.... to get to the lowest modules plus[/color]

Not at all -- you may perfectly well "import a.b.c.d as e" and use e as
the reference throughout the importing module.

But the point is, modules should be MODULAR (duh) -- if I 'import x' I
should NOT rely on what x itself imports (and so on transitively), just
on what x ``exports'', so to speak, at its TOP level. The Law of
Demeter in its simplified form "if you have more than one dot in your
reference you're doing things wrong" applies. In fact, the many-dots
form of module naming is intended for nested PACKAGES, *NOT* for
"modules which import each other".
[color=blue]
> that you'd have to check each module for imports outside this tree.[/color]

Why would you have to check any module for such "outside imports"? I
don't see the need for any checks.


If you just simply forget the very _existence_ of "from X import *",
your Python code can only grow better as a result. I earnestly hope it
disappears come Python 3.0 time...


Alex

[Bruno Desthuilliers]

Re: Confused about namespaces

KvS a écrit :[color=blue]
> Ok, makes sense but didn't seem "natural" to me,[/color]

It will seem more natural if you understand that modules should be
modulars (ie: low coupling, high cohesion). A module should *never*
bother about no rely upon other modules being imported by the module it
imports itself. Err, not quite clear... Let's rephrase it : a module
should only used symbols it defines itself or that it *explicitely*
imports from other modules.
[color=blue]
> although it is an
> obvious consequence of what you just pointed out, namely that modules
> are evaluated in their own namespace, something to keep in mind... On
> the other hand it does apparently work recursively "the other way
> around" since I didn't explicitly import wx in main.py but only
> indirect via importing GUIclasses in which wx is imported right?[/color]

You've already got technical answers to this - please carefully (re)read
Alex Martelli's post.

Now about coding style: this is *very* Bad Style(tm). Your main module
imports should look like this:

import wx
# import settings -> we don't use the settings module here
from GUIclasses import KFrame

(...)

and the GUIclasses module's import :

import wx
import wx.lib.mixins.l istctrl as listmix
import settings -> *here* we use the settings module

(...)

Python's philosophy is to favour readability.

Talking about imports, take time to open your Python interactive shell
and type "import this" !-)

[Bruno Desthuilliers]

Re: Confused about namespaces

KvS a écrit :[color=blue]
> Ok, makes sense but didn't seem "natural" to me,[/color]

It will seem more natural if you understand that modules should be
modulars (ie: low coupling, high cohesion). A module should *never*
bother about no rely upon other modules being imported by the module it
imports itself. Err, not quite clear... Let's rephrase it : a module
should only used symbols it defines itself or that it *explicitely*
imports from other modules.
[color=blue]
> although it is an
> obvious consequence of what you just pointed out, namely that modules
> are evaluated in their own namespace, something to keep in mind... On
> the other hand it does apparently work recursively "the other way
> around" since I didn't explicitly import wx in main.py but only
> indirect via importing GUIclasses in which wx is imported right?[/color]

You've already got technical answers to this - please carefully (re)read
Alex Martelli's post.

Now about coding style: this is *very* Bad Style(tm). Your main module
imports should look like this:

import wx
# import settings -> we don't use the settings module here
from GUIclasses import KFrame

(...)

and the GUIclasses module's import :

import wx
import wx.lib.mixins.l istctrl as listmix
import settings -> *here* we use the settings module

(...)

Python's philosophy is to favour readability.

Talking about imports, take time to open your Python interactive shell
and type "import this" !-)

[KvS]

Re: Confused about namespaces

Thanks a lot for all the answers. After rereading everything said here
today it's become more clear to me what you guys are telling me and
I'll actively try to forget about "from ... import *" ;).

[KvS]

Re: Confused about namespaces

Thanks a lot for all the answers. After rereading everything said here
today it's become more clear to me what you guys are telling me and
I'll actively try to forget about "from ... import *" ;).

[Alex Martelli]

Re: Confused about namespaces

KvS <keesvanschaik@ gmail.com> wrote:
[color=blue]
> Thanks a lot for all the answers. After rereading everything said here
> today it's become more clear to me what you guys are telling me and
> I'll actively try to forget about "from ... import *" ;).[/color]

I commend you for your decision. It's a construct that I sometimes find
quite handy in an experimentation session in the interactive
interpreter, but just has no really good place in 'true' code;-0.


Alex

[Alex Martelli]

Re: Confused about namespaces

KvS <keesvanschaik@ gmail.com> wrote:
[color=blue]
> Thanks a lot for all the answers. After rereading everything said here
> today it's become more clear to me what you guys are telling me and
> I'll actively try to forget about "from ... import *" ;).[/color]

I commend you for your decision. It's a construct that I sometimes find
quite handy in an experimentation session in the interactive
interpreter, but just has no really good place in 'true' code;-0.


Alex