On 6 March 2014 11:50, Brian May <[email protected]> wrote:
> Seems to be that there is more to it then that.
>
> For example. if in module/__init__.py I have:
>
> import module.something
>
> I get an circular import loop. The import "module.something" seems to
> imply an import of "module".
>
> However, if instead, I do:
>
> from module.something import somethingelse
>
> Then the circular import loop disappears.
>
> I have read that there are certain other cases where 'import package.name'
> will generate an error, but 'from package import name' won't.
>
Well, there is one common situation during import cycles where the reverse
is true.
Attempting to import a specific name before the module has bound it may
generate an error, but importing the (partially-initialised) module is fine.
For example, the following fails no matter what order your application
imports them in:
### mod2.py
from mod1 import f1
def f2():
pass
### mod1.py
from mod2 import f2
def f1():
pass
wheras, the following works fine regardless of the order the user
application imports them:
### mod3.py
import mod4
def f1(): mod4.f2()
def f3(): print 'woo'
### mod4.py
import mod3
def f2(): mod3.f3()
this is an uncommon enough problem that you don't often have to worry
about it. certainly at package level - __init__.py should contain almost
nothing, perhaps some documentation and an API import if you like.
--
William Leslie
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