What is init py for

Question

What is   init   py for in a Python source directory

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Since Python 3 3    init   py is no longer required to define directories as importable Python packages   Check PEP 420  Implicit Namespace Packages      Native support for package directories that don   t require   init   py marker files and can automatically span multiple path segments  inspired by various third party approaches to namespace packages  as described in PEP 420    Here s the test       mkdir -p  tmp test init   touch  tmp test init module py  tmp test init   init   py   tree -at  tmp test init  tmp test init  -- module py  --   init   py   python3   gt  gt  gt  import sys  gt  gt  gt  sys path insert 0    tmp    gt  gt  gt  from test init import module  gt  gt  gt  import test init module    rm -f  tmp test init   init   py   tree -at  tmp test init  tmp test init  -- module py   python3   gt  gt  gt  import sys  gt  gt  gt  sys path insert 0    tmp    gt  gt  gt  from test init import module  gt  gt  gt  import test init module   references  https   docs python org 3 whatsnew 3 3 html pep-420-implicit-namespace-packages https   www python org dev peps pep-0420  Is   init   py not required for packages in Python 3

User · Answer

One thing   init   py allows is converting a module to a package without breaking the API or creating extraneous nested namespaces or private modules   This helps when I want to extend a namespace  If I have a file util py containing def foo             then users will access foo with from util import foo  If I then want to add utility functions for database interaction  and I want them to have their own namespace under util  I ll need a new directory    and to keep API compatibility  so that from util import foo still works   I ll call it util   I could move util py into util  like so  util      init   py   util py   db py  and in util   init   py do from util import    but this is redundant  Instead of having a util util py file  we can just put the util py contents in   init   py and the user can now from util import foo from util db import check schema  I think this nicely highlights how a util package s   init   py acts in a similar way to a util module   this is hinted at in the other answers  but I want to highlight it here    short of employing import gymnastics  Note it won t work to create a new package with the same name as the file  see this

User · Answer

Although Python works without an   init   py file you should still include one  It specifies that the directory should be treated as a package  so therefore include it  even if it is empty   There is also a case where you may actually use an   init   py file  Imagine you had the following file structure  main methods       - methods py  And methods py contained this  def foo        return  foo   To use foo   you would need one of the following  from main methods methods import foo   Call with foo   from main methods import methods   Call with methods foo   import main methods methods   Call with main methods methods foo    Maybe there you need  or want  to keep methods py inside main methods  runtimes dependencies for example  but you only want to import main methods   If you changed the name of methods py to   init   py then you could use foo   by just importing main methods  import main methods print main methods foo      Prints  foo   This works because   init   py is treated as part of the package   Some Python packages actually do this   An example is with JSON  where running import json is actually importing   init   py from the json package  see the package file structure here    Source code  Lib json   init   py

User · Answer

Since Python 3 3    init   py is no longer required to define directories as importable Python packages   Check PEP 420  Implicit Namespace Packages      Native support for package directories that don   t require   init   py marker files and can automatically span multiple path segments  inspired by various third party approaches to namespace packages  as described in PEP 420    Here s the test       mkdir -p  tmp test init   touch  tmp test init module py  tmp test init   init   py   tree -at  tmp test init  tmp test init  -- module py  --   init   py   python3   gt  gt  gt  import sys  gt  gt  gt  sys path insert 0    tmp    gt  gt  gt  from test init import module  gt  gt  gt  import test init module    rm -f  tmp test init   init   py   tree -at  tmp test init  tmp test init  -- module py   python3   gt  gt  gt  import sys  gt  gt  gt  sys path insert 0    tmp    gt  gt  gt  from test init import module  gt  gt  gt  import test init module   references  https   docs python org 3 whatsnew 3 3 html pep-420-implicit-namespace-packages https   www python org dev peps pep-0420  Is   init   py not required for packages in Python 3

User · Answer

It used to be a required part of a package  old  pre-3 3  regular package   not newer 3 3   namespace package     Here s the documentation      Python defines two types of packages  regular packages and namespace packages  Regular packages are traditional packages as they existed in Python 3 2 and earlier  A regular package is typically implemented as a directory containing an   init   py file  When a regular package is imported  this   init   py file is implicitly executed  and the objects it defines are bound to names in the package   s namespace  The   init   py file can contain the same Python code that any other module can contain  and Python will add some additional attributes to the module when it is imported    But just click the link  it contains an example  more information  and an explanation of namespace packages  the kind of packages without   init   py

User · Answer

In Python the definition of package is very simple  Like Java the hierarchical structure and the directory structure are the same  But you have to have   init   py in a package  I will explain the   init   py file with the example below   package x   --    init   py  --    subPackage a   ------    init   py  ------  module m1 py  --    subPackage b   ------    init   py  ------  module n1 py  ------  module n2 py  ------  module n3 py     init   py can be empty  as long as it exists  It indicates that the directory should be regarded as a package  Of course    init   py can also set the appropriate content   If we add a function in module n1   def function X        print  function X in module n1      return   After running    gt  gt  gt from package x subPackage b module n1 import function X  gt  gt  gt function X    function X in module n1    Then we followed the hierarchy package and called module n1 the function  We can use   init   py in subPackage b like this     all       module n2    module n3     After running     gt  gt  gt from package x subPackage b import     gt  gt  gt module n1 function X    Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  ImportError  No module named module n1   Hence using   importing  module package is subject to   init   py content

User · Answer

There are 2 main reasons for   init   py   For convenience  the other users will not need to know your functions  exact location in your package hierarchy   your package      init   py   file1 py   file2 py           fileN py     in   init   py from file1 import   from file2 import       from fileN import       in file1 py def add        pass   then others can call add   by   from your package import add   without knowing file1  like  from your package file1 import add  If you want something to be initialized  for example  logging  which should be put in the top level    import logging config logging config dictConfig Your logging config

User · Answer

It used to be a required part of a package  old  pre-3 3  regular package   not newer 3 3   namespace package     Here s the documentation      Python defines two types of packages  regular packages and namespace packages  Regular packages are traditional packages as they existed in Python 3 2 and earlier  A regular package is typically implemented as a directory containing an   init   py file  When a regular package is imported  this   init   py file is implicitly executed  and the objects it defines are bound to names in the package   s namespace  The   init   py file can contain the same Python code that any other module can contain  and Python will add some additional attributes to the module when it is imported    But just click the link  it contains an example  more information  and an explanation of namespace packages  the kind of packages without   init   py

User · Answer

It facilitates importing other python files  When you placed this file in a directory  say stuff containing other py files  then you can do something like import stuff other   root      stuff           other py      morestuff           another py   Without this   init   py inside the directory stuff  you couldn t import other py  because Python doesn t know where the source code for stuff is and unable to recognize it as a package

User · Answer

In Python the definition of package is very simple  Like Java the hierarchical structure and the directory structure are the same  But you have to have   init   py in a package  I will explain the   init   py file with the example below   package x   --    init   py  --    subPackage a   ------    init   py  ------  module m1 py  --    subPackage b   ------    init   py  ------  module n1 py  ------  module n2 py  ------  module n3 py     init   py can be empty  as long as it exists  It indicates that the directory should be regarded as a package  Of course    init   py can also set the appropriate content   If we add a function in module n1   def function X        print  function X in module n1      return   After running    gt  gt  gt from package x subPackage b module n1 import function X  gt  gt  gt function X    function X in module n1    Then we followed the hierarchy package and called module n1 the function  We can use   init   py in subPackage b like this     all       module n2    module n3     After running     gt  gt  gt from package x subPackage b import     gt  gt  gt module n1 function X    Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  ImportError  No module named module n1   Hence using   importing  module package is subject to   init   py content

User · Answer

It facilitates importing other python files  When you placed this file in a directory  say stuff containing other py files  then you can do something like import stuff other   root      stuff           other py      morestuff           another py   Without this   init   py inside the directory stuff  you couldn t import other py  because Python doesn t know where the source code for stuff is and unable to recognize it as a package

User · Answer

The   init   py file makes Python treat directories containing it as modules    Furthermore  this is the first file to be loaded in a module  so you can use it to execute code that you want to run each time a module is loaded  or specify the submodules to be exported

User · Answer

init   py will treat the directory it is in as a loadable module   For people who prefer reading code  I put Two-Bit Alchemist s comment here     find  tmp mydir   tmp mydir   tmp mydir  spam  tmp mydir  spam   init   py  tmp mydir  spam module py   cd     python  gt  gt  gt  import sys  gt  gt  gt  sys path insert 0    tmp mydir    gt  gt  gt  from spam import module  gt  gt  gt  module myfun 3  9  gt  gt  gt  exit        rm  tmp mydir spam   init   py       python  gt  gt  gt  import sys  gt  gt  gt  sys path insert 0    tmp mydir    gt  gt  gt  from spam import module Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  ImportError  No module named spam  gt  gt  gt

User · Answer

The   init   py file makes Python treat directories containing it as modules    Furthermore  this is the first file to be loaded in a module  so you can use it to execute code that you want to run each time a module is loaded  or specify the submodules to be exported

User · Answer

The   init   py file makes Python treat directories containing it as modules    Furthermore  this is the first file to be loaded in a module  so you can use it to execute code that you want to run each time a module is loaded  or specify the submodules to be exported

User · Answer

In addition to labeling a directory as a Python package and defining   all      init   py allows you to define any variable at the package level  Doing so is often convenient if a package defines something that will be imported frequently  in an API-like fashion  This pattern promotes adherence to the Pythonic  flat is better than nested  philosophy   An example  Here is an example from one of my projects  in which I frequently import a sessionmaker called Session to interact with my database  I wrote a  database  package with a few modules   database        init   py     schema py     insertions py     queries py   My   init   py contains the following code   import os  from sqlalchemy orm import sessionmaker from sqlalchemy import create engine  engine   create engine os environ  DATABASE URL    Session   sessionmaker bind engine    Since I define Session here  I can start a new session using the syntax below  This code would be the same executed from inside or outside of the  database  package directory   from database import Session session   Session     Of course  this is a small convenience -- the alternative would be to define Session in a new file like  create session py  in my database package  and start new sessions using   from database create session import Session session   Session     Further reading  There is a pretty interesting reddit thread covering appropriate uses of   init   py here   http   www reddit com r Python comments 1bbbwk whats your opinion on what to include in init py   The majority opinion seems to be that   init   py files should be very thin to avoid violating the  explicit is better than implicit  philosophy

User · Answer

It used to be a required part of a package  old  pre-3 3  regular package   not newer 3 3   namespace package     Here s the documentation      Python defines two types of packages  regular packages and namespace packages  Regular packages are traditional packages as they existed in Python 3 2 and earlier  A regular package is typically implemented as a directory containing an   init   py file  When a regular package is imported  this   init   py file is implicitly executed  and the objects it defines are bound to names in the package   s namespace  The   init   py file can contain the same Python code that any other module can contain  and Python will add some additional attributes to the module when it is imported    But just click the link  it contains an example  more information  and an explanation of namespace packages  the kind of packages without   init   py

User · Answer

init   py will treat the directory it is in as a loadable module   For people who prefer reading code  I put Two-Bit Alchemist s comment here     find  tmp mydir   tmp mydir   tmp mydir  spam  tmp mydir  spam   init   py  tmp mydir  spam module py   cd     python  gt  gt  gt  import sys  gt  gt  gt  sys path insert 0    tmp mydir    gt  gt  gt  from spam import module  gt  gt  gt  module myfun 3  9  gt  gt  gt  exit        rm  tmp mydir spam   init   py       python  gt  gt  gt  import sys  gt  gt  gt  sys path insert 0    tmp mydir    gt  gt  gt  from spam import module Traceback  most recent call last     File   lt stdin gt    line 1  in  lt module gt  ImportError  No module named spam  gt  gt  gt

User · Answer

In addition to labeling a directory as a Python package and defining   all      init   py allows you to define any variable at the package level  Doing so is often convenient if a package defines something that will be imported frequently  in an API-like fashion  This pattern promotes adherence to the Pythonic  flat is better than nested  philosophy   An example  Here is an example from one of my projects  in which I frequently import a sessionmaker called Session to interact with my database  I wrote a  database  package with a few modules   database        init   py     schema py     insertions py     queries py   My   init   py contains the following code   import os  from sqlalchemy orm import sessionmaker from sqlalchemy import create engine  engine   create engine os environ  DATABASE URL    Session   sessionmaker bind engine    Since I define Session here  I can start a new session using the syntax below  This code would be the same executed from inside or outside of the  database  package directory   from database import Session session   Session     Of course  this is a small convenience -- the alternative would be to define Session in a new file like  create session py  in my database package  and start new sessions using   from database create session import Session session   Session     Further reading  There is a pretty interesting reddit thread covering appropriate uses of   init   py here   http   www reddit com r Python comments 1bbbwk whats your opinion on what to include in init py   The majority opinion seems to be that   init   py files should be very thin to avoid violating the  explicit is better than implicit  philosophy

User · Answer

It facilitates importing other python files  When you placed this file in a directory  say stuff containing other py files  then you can do something like import stuff other   root      stuff           other py      morestuff           another py   Without this   init   py inside the directory stuff  you couldn t import other py  because Python doesn t know where the source code for stuff is and unable to recognize it as a package

User · Answer

It used to be a required part of a package  old  pre-3 3  regular package   not newer 3 3   namespace package     Here s the documentation      Python defines two types of packages  regular packages and namespace packages  Regular packages are traditional packages as they existed in Python 3 2 and earlier  A regular package is typically implemented as a directory containing an   init   py file  When a regular package is imported  this   init   py file is implicitly executed  and the objects it defines are bound to names in the package   s namespace  The   init   py file can contain the same Python code that any other module can contain  and Python will add some additional attributes to the module when it is imported    But just click the link  it contains an example  more information  and an explanation of namespace packages  the kind of packages without   init   py

User · Answer

Files named   init   py are used to mark directories on disk as Python package directories  If you have the files  mydir spam   init   py mydir spam module py   and mydir is on your path  you can import the code in module py as  import spam module   or   from spam import module   If you remove the   init   py file  Python will no longer look for submodules inside that directory  so attempts to import the module will fail   The   init   py file is usually empty  but can be used to export selected portions of the package under more convenient name  hold convenience functions  etc  Given the example above  the contents of the init module can be accessed as   import spam   based on this

User · Answer

It facilitates importing other python files  When you placed this file in a directory  say stuff containing other py files  then you can do something like import stuff other   root      stuff           other py      morestuff           another py   Without this   init   py inside the directory stuff  you couldn t import other py  because Python doesn t know where the source code for stuff is and unable to recognize it as a package

User · Answer

An   init   py file makes imports easy  When an   init   py is present within a package  function a   can be imported from file b py like so   from b import a   Without it  however  you can t import directly  You have to amend the system path   import sys sys path insert 0   path to b py    from b import a

User · Answer

One thing   init   py allows is converting a module to a package without breaking the API or creating extraneous nested namespaces or private modules   This helps when I want to extend a namespace  If I have a file util py containing def foo             then users will access foo with from util import foo  If I then want to add utility functions for database interaction  and I want them to have their own namespace under util  I ll need a new directory    and to keep API compatibility  so that from util import foo still works   I ll call it util   I could move util py into util  like so  util      init   py   util py   db py  and in util   init   py do from util import    but this is redundant  Instead of having a util util py file  we can just put the util py contents in   init   py and the user can now from util import foo from util db import check schema  I think this nicely highlights how a util package s   init   py acts in a similar way to a util module   this is hinted at in the other answers  but I want to highlight it here    short of employing import gymnastics  Note it won t work to create a new package with the same name as the file  see this

User · Answer

An   init   py file makes imports easy  When an   init   py is present within a package  function a   can be imported from file b py like so   from b import a   Without it  however  you can t import directly  You have to amend the system path   import sys sys path insert 0   path to b py    from b import a

User · Answer

Files named   init   py are used to mark directories on disk as Python package directories  If you have the files  mydir spam   init   py mydir spam module py   and mydir is on your path  you can import the code in module py as  import spam module   or   from spam import module   If you remove the   init   py file  Python will no longer look for submodules inside that directory  so attempts to import the module will fail   The   init   py file is usually empty  but can be used to export selected portions of the package under more convenient name  hold convenience functions  etc  Given the example above  the contents of the init module can be accessed as   import spam   based on this

User · Answer

Although Python works without an   init   py file you should still include one  It specifies that the directory should be treated as a package  so therefore include it  even if it is empty   There is also a case where you may actually use an   init   py file  Imagine you had the following file structure  main methods       - methods py  And methods py contained this  def foo        return  foo   To use foo   you would need one of the following  from main methods methods import foo   Call with foo   from main methods import methods   Call with methods foo   import main methods methods   Call with main methods methods foo    Maybe there you need  or want  to keep methods py inside main methods  runtimes dependencies for example  but you only want to import main methods   If you changed the name of methods py to   init   py then you could use foo   by just importing main methods  import main methods print main methods foo      Prints  foo   This works because   init   py is treated as part of the package   Some Python packages actually do this   An example is with JSON  where running import json is actually importing   init   py from the json package  see the package file structure here    Source code  Lib json   init   py

User · Answer

There are 2 main reasons for   init   py   For convenience  the other users will not need to know your functions  exact location in your package hierarchy   your package      init   py   file1 py   file2 py           fileN py     in   init   py from file1 import   from file2 import       from fileN import       in file1 py def add        pass   then others can call add   by   from your package import add   without knowing file1  like  from your package file1 import add  If you want something to be initialized  for example  logging  which should be put in the top level    import logging config logging config dictConfig Your logging config

User · Answer

The   init   py file makes Python treat directories containing it as modules    Furthermore  this is the first file to be loaded in a module  so you can use it to execute code that you want to run each time a module is loaded  or specify the submodules to be exported

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