That's a great question! It highlights the fundamental duality of the Python programming language.

The short answer is: Python is both open and closed.

These two terms refer to completely different aspects of the language. Let's break it down.

Python is "Open" (Open Source)

This is the most common meaning and refers to the licensing and development model of the Python language itself.

• Open Source License: Python is governed by the Python Software Foundation License (PSFL), which is an open-source license. This means:

  
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  • Free to Use: Anyone can use Python for any purpose, including commercial applications, without paying a license fee.
  • Free to Modify: Anyone can view the source code, modify it, and create their own versions of Python.
  • Free to Distribute: Anyone can share the Python interpreter and its source code with others.

• Open Development Model: The development of Python is highly transparent and community-driven.

  • Public Source Code: The source code is publicly available on platforms like GitHub.
  • Community Input: Anyone can report bugs, suggest new features, and contribute code to the project. The core development team reviews and merges these contributions.
  • PEP Process: New features and major changes are proposed through Python Enhancement Proposals (PEPs), which are publicly discussed before being accepted.

In summary, "open" means the Python language is a free, community-owned project with no corporate lock-in.

Python is "Closed" (as in a Closed Box)

This refers to the runtime environment and the CPython implementation. When you run a Python script, you are interacting with a "closed box" in the sense that you don't see the inner workings.

• The CPython Interpreter: Most people use CPython, the standard and most common implementation of Python, which is written in the C programming language.
  • Abstraction Layer: You, the Python programmer, write code in a high-level, human-readable language. You don't need to know the complex C code that makes your Python commands work.
  • Pre-compiled: When you run a Python file (.py), the CPython interpreter first compiles it into bytecode (.pyc files). This bytecode is then executed by the Python Virtual Machine (PVM). This bytecode is not human-readable and is a "closed" representation of your code.
  • Performance-Critical Parts: For performance, many of Python's core libraries (like those for handling numbers, lists, and strings) are implemented in C. As a user, you just call the Python functions, but the heavy lifting is done in a pre-compiled, "closed" C library.

In summary, "closed" means that as a user, you are shielded from the low-level complexities of the interpreter and its internal components. You interact with a clean, stable API, not the raw source code.

Analogy: A Car

Think of Python like a modern car:

• Open (Open Source):

  • The car's design (the Python language standard) is public.
  • Anyone can learn how the engine works (read the source code).
  • Engineers can modify the engine design and propose improvements to the car manufacturer (contribute to the project).
  • You can buy the car without a special license (free to use).

• Closed (Closed Box):

  • You, the driver, don't need to be a mechanic to drive the car. You just use the steering wheel, pedals, and dashboard (the Python API).
  • You don't see the thousands of individual explosions happening in the engine cylinders when you press the gas (the C code execution).
  • You can't easily see or modify the complex Engine Control Unit (ECU) software (the CPython interpreter's bytecode and C extensions).

Conclusion

So, when someone says "Python is open and closed," they are correct. It's a matter of perspective:

• Open refers to its licensing, development, and philosophy.
• Closed refers to the abstraction and implementation of its runtime environment.