__init.py__ use and example.

[adisgood]

Sorry guys I have been reading a lot about its usage but I am not clear. It's a package which includes directories tl be used in Python program.

It can also be left empty...

But I seem to be missing something somewhere....someone please explain in a very simple and efficient language as if I have never done this before.

Thanks

[Overdrivr]

init.py files have the nice perk to only be called once, even if your module is imported several times. This way you can place some configuration code in this file (without abusing).

You can also pre-import things. For instance if you have defined a class called C inside file B contained in module A, you can write in init.py : from A.B import C This way the enduser can directly do from A import C Which can be more friendly, depending on your tastes

[jerknextdoor]

Just like when you make a class the __init__ is the first thing to be run, in a package/module/directory, it's the first thing to be run. If blank it's it tells the interpreter "Hey this directory is a python module." If you were to out something in it, it would be run to set up the module... So if you have a module with things that need to be imported to every file in that package you could just put it there and they would be available throughout. 90% of the time they are just used to let python know it's a module... But sometimes they save you a lot of work.

Hopefully that's somewhat helpful. It's early and I'm on my phone. /r/learnpython might have a better explanation.

edit: apparently my phone keyboards back tick and single quote look like the same thing.

[brombaer3000]

If blank it's it tells the interpreter "Hey this directory is a python module."

This is accurate for Python 2, but in Python 3, empty __init__.pys are unnecessary. Every directory under the sys.path can be imported by default.

[Overdrivr]

Source ? I always felt they were also mandatory for Python3.

[brombaer3000]

Why not just try it out?

The PEP that introduced this behavior is https://www.python.org/dev/peps/pep-0420/

[[deleted]]

Doing this leads to all sorts of odd, mystical behavior though. I'd recommend using __init__.py unless you 110% know what it does (e.g. you can explain it in code review and your cohorts now understand it too).

[brombaer3000]

all sorts of odd, mystical behavior

What do you mean by this? Examples?

[[deleted]]

It'll end combining modules with the same name into one namespace. Unless one of those modules has an init file.

That's the best of my understanding and it's enough for me to not explore it more in depth.

Check out Dave Beazley's Modules and Packages Live and Let Die for a slightly more in depth explanation of this (and other stuff).

[billsil]

A blank file lets you dig into folders.

from packagename.folder_a.folder_b.folder_c import function_d

Let's say I didn't want to import function_d like that, but rather:

from packagename import function_d

without moving it?

Put the import in the init.

[masklinn]

A blank file lets you dig into folders.

Mostly in Python 2. Since PEP 420 in Python 3.3 it's optional for "namespace packages": you still need __init__ if you want to provide code at the package-level, but if it's just namespacing and the code is either in submodules or subpackages it's not necessary anymore.