__init__.py
__init__.py is a Python package module that may initialize a package’s namespace and behavior when the package is imported.
The Well-Grounded Python Developer: How the pros use Python and Flask
An __init__.py file is a Python package file that marks a directory as a package and may contain package initialization code.
- How it is used
- Organizes related Python modules into importable packages and supports a Flask application factory.
- How deep it goes
- Defines the file’s package role, explains its execution during imports, and works through utility and application layouts without exploring import internals.
- Examples
- Uses a string utility moved into a package and a Flask application reorganized around an app package.
- What you can do after
- Build it from scratch by adding __init__.py to a directory, then import its modules or expose a Flask app factory.
The Quick Python Book, Fourth Edition
An __init__.py file is a Python package file that can contain initialization code executed when the package is imported.
- How it is used
- Uses __init__.py to mark package directories and run initialization when packages are first loaded.
- How deep it goes
- Explains first-load execution, package attributes, nested imports, and __all__ through examples, without detailing import machinery internals.
- Examples
- Demonstrates initialization messages, a package version attribute, nested imports, and wildcard imports with a small package tree.
- What you can do after
- Build it from scratch: create an empty or populated __init__.py, then choose explicit imports or __all__ for package access.
Read how The Quick Python Book, Fourth Edition explains __init__.py →
Python Workout: 50 ten-minute exercises
__init__.py is the conventional initialization file whose execution initializes a Python package when the package is imported.
- How it is used
- Initializes a Python package when importing the package and can expose its internal modules.
- How deep it goes
- Defines initialization through executing __init__.py, but does not detail its contents beyond importing internal modules.
- Examples
- Uses mypackage with first.py, second.py, third.py, and several import forms.
- What you can do after
- Apply it by placing __init__.py in a package and importing internal modules through package-level forms.
Read how Python Workout: 50 ten-minute exercises explains __init__.py →
Python Workout, Second Edition
__init__.py is a conventional Python package file whose code is executed when the containing package is imported.
- How it is used
- Groups related Python modules and runs package initialization code during package imports.
- How deep it goes
- Explains package recognition, initialization, and module imports, but does not detail execution order or advanced package configuration.
- Examples
- Uses mypackage with first.py, second.py, third.py, and alternative import statements.
- What you can do after
- Build it from scratch by organizing modules into a package and selecting direct or qualified import forms.
Read how Python Workout, Second Edition explains __init__.py →
Related concepts
- packageconfigures · A software package is a named grouping of modules or components, often with related resources and metadata, organized for import, reuse, distribution, or management.
- packageconfigures · A package is a programming-language namespace and organizational unit that groups related code and may define import, compilation, or access boundaries.
- side effectproduces · A software side effect is an observable change or interaction caused by an operation beyond producing its direct result, such as modifying state or performing input or output.
- file objectkind of · A file object is a program-accessible representation of an open file or stream, including its access state and input/output operations.
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