python: is there a disadvantage to from package import * besides namespace collision

I'm creating a class to extend a package, and prior to class instantiation I don't know which subset of the package's namespace I need. I've been careful about avoiding namespace conflicts in my code, so, does

from package import * 

create problems besides name conflicts?

Is it better to 开发者_运维知识库examine the class's input and import only the names I need (at runtime) in the __init__ ??

Can python import from a set [] ?

does

for name in [namespace,namespace]:
    from package import name

make any sense?

I hope this question doesn't seem like unnecessary hand-ringing, i'm just super new to python and don't want to do the one thing every 'beginnger's guide' says not to do (from pkg import * ) unless I'm sure there's no alternative.

thoughts, advice welcome.

In order:

• It does not create other problems - however, name conflicts can be much more of a problem than you'd expect.

• Definitely defer your imports if you can. Even though Python variable scoping is simplistic, you also gain the benefit of not having to import the module if the functionality that needs it never gets called.

• I don't know what you mean. Square brackets are used to make lists, not sets. You can import multiple names from a module in one line - just use a comma-delimited list:

  from awesome_module import spam, ham, eggs, baked_beans
  # awesome_module defines lots of other names, but they aren't pulled in.
  

• No, that won't do what you want - name is an identifier, and as such, each time through the loop the code will attempt to import the name name, and not the name that corresponds to the string referred to by the name variable.

However, you can get this kind of "dynamic import" effect, using the __import__ function. Consult the documentation for more information, and make sure you have a real reason for using it first. We get into some pretty advanced uses of the language here pretty quickly, and it usually isn't as necessary as it first appears. Don't get too clever. We hates them tricksy hobbitses.

When importing * you get everything in the module dumped straight into your namespace. This is not always a good thing as you could accentually overwrite something like;

from time import *
sleep = None

This would render the time.sleep function useless...

The other way of taking functions, variables and classes from a module would be saying

from time import sleep

This is a nicer way but often the best way is to just import the module and reference the module directly like

import time
time.sleep(3)

you can import like from PIL import Image, ImageDraw

what is imported by from x import * is limited to the list __all__ in x if it exists

importing at runtime if the module name isn't know or fixed in the code must be done with __import__ but you shouldn't have to do that

This syntax constructions help you to avoid any name collision:

from package import somename as another_name
import package as another_package_name