[Python-ideas] How exactly does from ... import ... work?

[Chris Angelico]

On Tue, Jan 5, 2016 at 4:32 PM, u8y7541 The Awesome Person
<surya.subbarao1 at gmail.com> wrote:
> Suppose I have a file called randomFile.py which reads like this:
> class A:
>     def __init__(self, foo):
>         self.foo = foo
>         self.bar = bar(foo)
> class B(A):
>     pass
> class C(B):
>     pass
> def bar(foo):
>     return foo + 1
>
> Suppose in another file in the same directory, I have another python
> program.
>
> from randomFile import C
>
> # some code
>
> When C has to be imported, B also has to be imported because it is the
> parent. Therefore, A also has to be imported. This also results in the
> function bar being imported. When from ... import ... is called, does Python
> follow all the references and import everything that is needed, or does it
> just import the whole namespace (making wildcard imports acceptable :O)?
>

Not sure why this is on -ideas; explanations of how Python already
works would more normally go on python-list.

When you say "from X import Y", what Python does is, more-or-less:

import Y
X = Y.X
del Y

The entire file gets executed, and then one symbol from it gets
imported into the current namespace.

ChrisA