Is init py not required for packages in Python 3 3

Question

I am using Python 3 5 1  I read the document and the package section here  https   docs python org 3 tutorial modules html packages  Now  I have the following structure    home wujek Playground a b module py   module py   class Foo      def   init   self           print  initializing Foo     Now  while in  home wujek Playground     Playground   python3  gt  gt  gt  import a b module  gt  gt  gt  a b module Foo   initializing Foo  lt a b module Foo object at 0x100a8f0b8 gt    Similarly  now in home  superfolder of Playground       PYTHONPATH Playground python3  gt  gt  gt  import a b module  gt  gt  gt  a b module Foo   initializing Foo  lt a b module Foo object at 0x10a5fee10 gt    Actually  I can do all kinds of stuff       PYTHONPATH Playground python3  gt  gt  gt  import a  gt  gt  gt  import a b  gt  gt  gt  import Playground a b   Why does this work  I though there needed to be   init   py files  empty ones would work  in both a and b for module py to be importable when the Python path points to the Playground folder   This seems to have changed from Python 2 7       PYTHONPATH Playground python  gt  gt  gt  import a ImportError  No module named a  gt  gt  gt  import a b ImportError  No module named a b  gt  gt  gt  import a b module ImportError  No module named a b module   With   init   py in both   Playground a and   Playground a b it works fine

User · Answer

I would say that one should omit the   init   py only if one wants to have the implicit namespace package  If you don t know what it means  you probably don t want it and therefore you should continue to use the   init   py even in Python 3

User · Answer

Overview  Mike s answer is correct but too imprecise  It is true that Python 3 3  supports Implicit Namespace Packages that allows it to create a package without an   init   py file  This is called a namespace package in contrast to a regular package which does have an   init   py file  empty or not empty   However  creating a namespace package should ONLY be done if there is a need for it  For most use cases and developers out there  this doesn t apply so you should stick with EMPTY   init   py files regardless  Namespace package use case To demonstrate the difference between the two types of python packages  lets look at the following example  google pubsub                lt - Package 1     google                   lt - Namespace package  there is no   init   py          cloud                lt - Namespace package  there is no   init   py              pubsub           lt - Regular package  with   init   py                    init   py  lt - Required to make the package a regular package                 foo py  google storage               lt - Package 2     google                   lt - Namespace package  there is no   init   py          cloud                lt - Namespace package  there is no   init   py              storage          lt - Regular package  with   init   py                    init   py  lt - Required to make the package a regular package                 bar py  google pubsub and google storage are separate packages but they share the same namespace google cloud  In order to share the same namespace  it is required to make each directory of the common path a namespace package  i e  google  and cloud   This should be the only use case for creating namespace packages  otherwise  there is no need for it  It s crucial that there are no   init  py files in the google and google cloud directories so that both directories can be interpreted as namespace packages  In Python 3 3  any directory on the sys path with a name that matches the package name being looked for will be recognized as contributing modules and subpackages to that package  As a result  when you import both from google pubsub and google storage  the Python interpreter will be able to find them  This is different from regular packages which are self-contained meaning all parts live in the same directory hierarchy  When importing a package and the Python interpreter encounters a subdirectory on the sys path with an   init   py file  then it will create a single directory package containing only modules from that directory  rather than finding all appropriately named subdirectories outside that directory  This is perfectly fine for packages that don t want to share a namespace  I highly recommend taking a look at Traps for the Unwary in Python   s Import System to get a better understanding of how Python importing behaves with regular and namespace package and what   init   py traps to watch out for  Summary  Only skip   init   py files if you want to create namespace packages  Only create namespace packages if you have different libraries that reside in different locations and you want them each to contribute a subpackage to the parent package  i e  the namespace package  Keep on adding empty   init  py to your directories because 99  of the time you just want to create regular packages  Also  Python tools out there such as mypy and pytest require empty   init   py files to interpret the code structure accordingly  This can lead to weird errors if not done with care   Resources My answer only touches the surface of how regular packages and namespace packages work so take a look at the following resources for further information   PEP 420 -- Implicit Namespace Packages The import system - Regular packages The import system - Namespace packages Traps for the Unwary in Python   s Import System

User · Answer

Based on my experience  even with python 3 3   an empty   init   py is still needed sometimes  One situation is when you want to refer a subfolder as a package  For example  when I ran python -m test foo  it didn t work until I created an empty   init   py under the test folder  And I m talking about 3 6 6 version here which is pretty recent  Apart from that  even for reasons of compatibility with existing source code or project guidelines  its nice to have an empty   init   py in your package folder

User · Answer

Python 3 3  has Implicit Namespace Packages that allow it to create a packages without an   init   py file      Allowing implicit namespace packages means that the requirement to provide an   init   py file can be dropped completely  and affected          The old way with   init   py files still works as in Python 2

User · Answer

If you have setup py in your project and you use find packages   within it  it is necessary to have an   init   py file in every directory for packages to be automatically found      Packages are only recognized if they include an   init   py file   UPD  If you want to use implicit namespace packages without   init   py you just have to use find namespace packages   instead  Docs

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