Python import questions

[clapperboy]

Hello, I'm a mel user learning python.
I've started to read diveintopython and How to Think Like a Computer Scientist: Learning with Python v2nd Edition documentation

Concerning python import command to import module
Here's a few assumptions I gathered from my reading. If an experienced user could comment them, i'd really appreciate it.

import maya

This will import the entire maya moduleI can then run the ls command by calling the full maya.cmds namespace

maya.cmds.ls("*")

from maya import cmds

This import maya.cmds as cmds.
The relation inbetween maya and cmds is stated in the import line.Someone reading the script would know that cmds comes from maya.
I can then run the ls command by calling cmds

cmds.ls("*")

from maya import *

This import the full maya module as well, but gets rid of the relation inbetween maya and cmds. So unless someone has the knowledge that cmds belongs to maya, there is no way of knowing by simply reading the script. My guess is that there must be a way to figure the relation with some command unknown to me at the moment.
I can then run the ls command by calling cmds

cmds.ls("*")

from maya.cmds import *

This import the maya.cmds, and let you run the ls command straight. 

ls("*")

Here again, I find that someone reading the script cant tell where the ls comes from.

So it feels to me that using the from module import * is a bad habit.
Sure it saves you some typing, but it makes it harder to figure out from which module a command comes from by reading the script.
Obviously if you import only one module, its pretty easy to figure out where the command comes from, but I see this method becoming problematic as you import multiple modules.
I suppose it could create namespace clashing if there is a def that has the same name in 2 different modules.

If you import 2 module with the from module import *, and those module have both a ls def, how does python handles this? Simple runTime error? or is there a sequence? like the first import line has precedence over the second one.

from moduleA import *
from moduleB import *

if a ls def exists in both module, which ls gets run?

I'm gonna test this out later, but in the mean time, if an experienced python programmer could give advice as to what is the best way to use the import command. I'd really appreciate it. I'd like to get into good habit right away

P.S. hopefully I've used the correct term in my description.

[joojaa]

So unless someone has the knowledge that cmds belongs to maya,
there is no way of knowing by simply reading the script.

Well likewise if you did

import sys as * nobody would know.

in fact if somebody just did

import sys

nobody would KNOW what sys is. (that is theyd assume its something usefull if they needed to actually know what it is theyd ASK PYTHON)

In reality theres no such problem. All even slightly proficient coders would do the module level import at the very first lines of any file. So whenever somebodey treads they'd go... oh that was imported. It doesnt really matter what modlue you importred not and how since in reality a 3rd party user might not know what the module holds anyway. But that dont matter anyway because you dont actually need to know what code calls to read an understand it, if you must then the code is badly done.

from moduleA import *
from moduleB import *
if a ls def exists in both module, which ls gets run?

moduleB's declaration. See thing is the definition is a dictionary so if you do:

d={}
d["foo"]=10
d["foo"]=1
d["foo"]
result: 1

anyway if you do:

print(ls)

python will tell you what the command ls is.

Here again, I find that someone reading the script cant tell where the ls comes from.

Now you can NEVER actually depend on any function doing what you think it does, somebody may inject into your code observe:

import maya.cmds as cmds

cmds.ls = lambda *args, **dict: "called cmds.ls with "+" ".join([str(i) for i in args, dict])
print(cmds.ls('*'))

cmds.ls is nolonger what you need it to be. Please note each file is in itts owna namespace so i just tainted the file i used here. (or global if you run it in console)

this opens up a usefull feature. you can wrap around commands with other commands now if you ran the code above in maya you tainted your global namespace dont worry it will reset when you restart.

See for example:

http://www.artima.com/weblogs/viewpost.jsp?thread=240808

So to recap you can never know what a piece of code does, you can only try to hope tthe code is self explanatory. If not then whoever wrote it is a idiot. See you choose your level of abstraction and only go into what you think is relevant based on what you read. Lot of magic can be done, but should not be done because people meed to be bale toread it.