Question

Out of the various ways to import code, are there some ways that are preferable to use, compared to others? This link http://effbot.org/zone/import-confusion.htm in short
states that

from foo.bar import MyClass

is not the preferred way to import MyClass under normal circumstances or unless you know what you are doing. Rather, a better way would like:

import foo.bar as foobaralias

and then in the code, to access MyClass use

foobaralias.MyClass

In short, it seems that the above-referenced link is saying it is usually better to import everything from a module, rather than just parts of the module.

However, that article I linked is really old.

I’ve also heard that it is better, at least in the context of Django projects, to instead only import the classes you want to use, rather than the whole module. It has been said that this form helps avoid circular import errors or at least makes the django import system less fragile. It was pointed out that Django’s own code seems to prefer "from x import y" over "import x".

Assuming the project I am working on doesn’t use any special features of __init__.py … (all of our __init__.py files are empty), what import method should I favor, and why?

Answer 1

For me, it’s dependent on the situation. If it’s a uniquely named method/class (i.e., not process() or something like that), and you’re going to use it a lot, then save typing and just do from foo import MyClass.

If you’re importing multiple things from one module, it’s probably better to just import the module, and do module.bar, module.foo, module.baz, etc., to keep the namespace clean.

You also said

It has been said that this form helps avoid circular import errors or at least makes the django import system less fragile. It was pointed out that Django’s own code seems to prefer “from x import y” over “import x”.

I don’t see how one way or the other would help prevent circular imports. The reason is that even when you do from x import y, ALL of x is imported. Only y is brought into the current namespace, but the entire module x is processed. Try out this example:

In test.py, put the following:

def a():
    print "a"

print "hi"

def b():
    print "b"

print "bye"

Then in ‘runme.py’, put:

from test import b

b()

Then just do python runme.py

You’ll see the following output:

hi
bye
b

So everything in test.py was run, even though you only imported b