'from X import a' versus 'import X; X.a'

Question

I've seen some Python programmers use the following style fairly consistently (we'll call it style 1):

import some_module
# Use some_module.some_identifier in various places.

For support of this style, you can cite the "explicit is better than implicit" maxim. I've seen other programmers use this style (style 2):

from some_module import some_identifier
# Use some_identifier in various places.

The primary benefit that I see in style 2 is maintainability -- especially with duck typing ideals I may want to swap some_module for some_other_module. I also feel style 2 wins points with the "readability counts" maxim. Although I tend to disagree, one can always argue that search-and-replace is just as good an option when using the first style.

Addendum: It was noted that you could use as to solve the switch from some_module to some_other_module in style 1. I forgot to mention that it is also common to decide to implement some_identifier in your current module, which makes creation of an equivalent some_module container slightly awkward.

Answer 1

There are uses for both cases, so I don't think this is an either-or issue. I'd consider using from module import x,y,z when:

• There are a fairly small number of things to import

• The purpose of the functions imported is obvious when divorced from the module name. If the names are fairly generic, they may clash with others and tell you little. eg. seeing remove tells you little, but os.remove will probably hint that you're dealing with files.

• The names don't clash. Similar to the above, but more important. Never do something like:

   from os import open
  

import module [as renamed_module] has the advantage that it gives a bit more context about what is being called when you use it. It has the disadvantage that this is a bit more cluttered when the module isn't really giving more information, and is slightly less performant (2 lookups instead of 1).

It also has advantages when testing however (eg. replacing os.open with a mock object, without having to change every module), and should be used when using mutable modules, e.g.

import config
config.dburl = 'sqlite:///test.db'

If in doubt, I'd always go with the import module style.