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It's just personal preference really, and has to do with the layout of your python modules.

Let's say you have a module called erikutils. There are two ways that it can be a module, either you have a file called erikutils.py on your sys.path or you have a directory called erikutils on your sys.path with an empty __init__.py file inside it. Then let's say you have a bunch of modules called fileutils, procutils, parseutils and you want those to be sub-modules under erikutils. So you make some .py files called fileutils.py, procutils.py, and parseutils.py:

erikutils
 __init__.py
 fileutils.py
 procutils.py
 parseutils.py

Maybe you have a few functions that just don't belong in the fileutils, procutils, or parseutils modules. And let's say you don't feel like creating a new module called miscutils. AND, you'd like to be able to call the function like so:

erikutils.foo()
erikutils.bar()

rather than doing

erikutils.miscutils.foo()
erikutils.miscutils.bar()

So because the erikutils module is a directory, not a file, we have to define it's functions inside the __init__.py file.

In django, the best example I can think of is django.db.models.fields. ALL the django *Field classes are defined in the __init__.py file in the django/db/models/fields directory. I guess they did this because they didn't want to cram everything into a hypothetical django/db/models/fields.py model, so they split it out into a few submodules (related.py, files.py, for example) and they stuck the made *Field definitions in the fields module itself (hence, __init__.py).

NOTE: Alexander Kojevnikov's answer doesn't really answer the question, and while he pointed out that you can access the sub-modules imports if you import them in the parent module but this is no different than a .py file-style module and is nothing unique to __init__.py for directory-style modules; however, it is a common pattern/use-case. And without the import something in the __init__.py you can still do import dir.something, while his post could be interpreted as meaning that it is not possible to get at the something modules without first importing it in __init__.py.

It's just personal preference really, and has to do with the layout of your python modules.

Let's say you have a module called erikutils. There are two ways that it can be a module, either you have a file called erikutils.py on your sys.path or you have a directory called erikutils on your sys.path with an empty __init__.py file inside it. Then let's say you have a bunch of modules called fileutils, procutils, parseutils and you want those to be sub-modules under erikutils. So you make some .py files called fileutils.py, procutils.py, and parseutils.py:

erikutils
 __init__.py
 fileutils.py
 procutils.py
 parseutils.py

Maybe you have a few functions that just don't belong in the fileutils, procutils, or parseutils modules. And let's say you don't feel like creating a new module called miscutils. AND, you'd like to be able to call the function like so:

erikutils.foo()
erikutils.bar()

rather than doing

erikutils.miscutils.foo()
erikutils.miscutils.bar()

So because the erikutils module is a directory, not a file, we have to define it's functions inside the __init__.py file.

In django, the best example I can think of is django.db.models.fields. ALL the django *Field classes are defined in the __init__.py file in the django/db/models/fields directory. I guess they did this because they didn't want to cram everything into a hypothetical django/db/models/fields.py model, so they split it out into a few submodules (related.py, files.py, for example) and they stuck the made *Field definitions in the fields module itself (hence, __init__.py).

It's just personal preference really, and has to do with the layout of your python modules.

Let's say you have a module called erikutils. There are two ways that it can be a module, either you have a file called erikutils.py on your sys.path or you have a directory called erikutils on your sys.path with an empty __init__.py file inside it. Then let's say you have a bunch of modules called fileutils, procutils, parseutils and you want those to be sub-modules under erikutils. So you make some .py files called fileutils.py, procutils.py, and parseutils.py:

erikutils
 __init__.py
 fileutils.py
 procutils.py
 parseutils.py

Maybe you have a few functions that just don't belong in the fileutils, procutils, or parseutils modules. And let's say you don't feel like creating a new module called miscutils. AND, you'd like to be able to call the function like so:

erikutils.foo()
erikutils.bar()

rather than doing

erikutils.miscutils.foo()
erikutils.miscutils.bar()

So because the erikutils module is a directory, not a file, we have to define it's functions inside the __init__.py file.

In django, the best example I can think of is django.db.models.fields. ALL the django *Field classes are defined in the __init__.py file in the django/db/models/fields directory. I guess they did this because they didn't want to cram everything into a hypothetical django/db/models/fields.py model, so they split it out into a few submodules (related.py, files.py, for example) and they stuck the made *Field definitions in the fields module itself (hence, __init__.py).

It's just personal preference really, and has to do with the layout of your python modules.

Let's say you have a module called erikutils. There are two ways that it can be a module, either you have a file called erikutils.py on your sys.path or you have a directory called erikutils on your sys.path with an empty __init__.py file inside it. Then let's say you have a bunch of modules called fileutils, procutils, parseutils and you want those to be sub-modules under erikutils. So you make some .py files called fileutils.py, procutils.py, and parseutils.py:

erikutils
 __init__.py
 fileutils.py
 procutils.py
 parseutils.py

Maybe you have a few functions that just don't belong in the fileutils, procutils, or parseutils modules. And let's say you don't feel like creating a new module called miscutils. AND, you'd like to be able to call the function like so:

erikutils.foo()
erikutils.bar()

rather than doing

erikutils.miscutils.foo()
erikutils.miscutils.bar()

So because the erikutils module is a directory, not a file, we have to define it's functions inside the __init__.py file.

In django, the best example I can think of is django.db.models.fields. ALL the django *Field classes are defined in the __init__.py file in the django/db/models/fields directory. I guess they did this because they didn't want to cram everything into a hypothetical django/db/models/fields.py model, so they split it out into a few submodules (related.py, files.py, for example) and they stuck the made *Field definitions in the fields module itself (hence, __init__.py).

NOTE: Alexander Kojevnikov's answer doesn't really answer the question, and while he pointed out that you can access the sub-modules imports if you import them in the parent module but this is no different than a .py file-style module and is nothing unique to __init__.py for directory-style modules; however, it is a common pattern/use-case. And without the import something in the __init__.py you can still do import dir.something, while his post could be interpreted as meaning that it is not possible to get at the something modules without first importing it in __init__.py.