Python: Import * only imports certain things from package?

Question

I've got a package called elements that contains some stuff like button, trifader, poster. In the Button class, I am doing from elements import *

This executes OK, and when I try to print(poster), also works OK and functions as expected. However, when I do print(trifader), NameError: name 'trifader' is not defined. Even though trifader and poster are in the same package, poster is defined, but trifader isn't? How weird. Is there any explanation for this?

The directory structure of the elements package is this:

Elements:
  __init__.py
  trifader.py
  button.py
  poster.py

Also, some other stuff that isn't really relevant.

Each .py file contains a class with the name of the .py, for example, trifader.py has a class called TriFader.

Perhaps `__all__` is used? http://stackoverflow.com/questions/44834/can-someone-explain-all-in-python — Code Painters, Nov 08 '12 at 01:03
Is `trifader` a class, a .py file or a package? Please provide your directory structure with the location of all `.py` files and the class names that are defined within each of them. It's difficult to say anything meaningful without this information. — John Lyon, Nov 08 '12 at 01:03
As a general rule, it's pretty bad practice to use `from x import *` in python. — Daenyth, Nov 08 '12 at 01:12
@daenyth I know, but I think this is one of the times to use it.. :\ — Name McChange, Nov 08 '12 at 01:15

score 2 · Accepted Answer · answered Nov 08 '12 at 01:11

2

If your __init__.py doesn't have __all__ defined (thus restricting what is imported using from X import *), then you probably have a circular import somewhere which is causing a module to be referenced before its' definitions have been evaluated.

answered Nov 08 '12 at 01:11

Nick Bastin

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Raunak Agarwal · Answer 2 · 2012-11-08T02:20:29.563

0

Check for circular imports. Circular imports are fine where both modules use the “import ” form of import. They fail when the 2nd module wants to grab a name out of the first (“from module import name”) and the import is at the top level. That’s because names in the 1st are not yet available, because the first module is busy importing the 2nd. Secondly, if the import is called inside the function by the time the import is called, the first module will have finished initializing, and the second module can do its import.

edited Nov 08 '12 at 02:20

answered Nov 08 '12 at 01:13

Raunak Agarwal

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Circular imports aren't necessarily fine when both use the non-star `import` form - if you have class definitions in both modules which require names from the other module you will also have a problem. The only case in which is a circular import is "fine" is when names don't need to be resolved until runtime (when both modules are already instantiated), as opposed to compile time (when their members are used in the instantiation of another definition). – Nick Bastin Nov 08 '12 at 02:11

Python: Import * only imports certain things from package?

2 Answers2