Excellent question. This is a crucial decision for anyone starting with Python today.

The short, direct answer is: You should learn and use Python 3.

Python 2 is officially unsupported and considered a legacy technology. Here’s a detailed breakdown of why, covering the key differences and the practical implications for you.

The Executive Summary: Python 3 is the Present and Future

Detailed Explanation of Key Differences

Understanding why these changes were made will help you appreciate Python 3.

The print Statement vs. Function

This is the most visible change.

• Python 2: print "Hello, World!" is a statement.
• Python 3: print("Hello, World!") is a function.

The function version is more powerful. For example, you can easily redirect output:

# Python 3
print("Hello", "World", sep="-", end="!\n") # Prints: Hello-World!

Doing this in Python 2 requires a more verbose from __future__ import print_function.

Integer Division

This is a major source of bugs for those moving from Python 2 to 3.

• Python 2: 5 / 2 results in 2. It automatically truncates the decimal part. This can lead to unexpected mathematical errors.
• Python 3: 5 / 2 results in 5. It performs "true" division. If you want integer division, you use the floor division operator: 5 // 2 results in 2.

This change makes Python behave more like a standard calculator and avoids subtle bugs in scientific and financial computing.

Unicode Support

This is arguably the most important improvement.

• Python 2: The default string type (str) is a sequence of bytes. To handle international characters, you must use the unicode type. This leads to a lot of confusion and UnicodeDecodeError and UnicodeEncodeError exceptions.
• Python 3: The default string type (str) is a sequence of Unicode characters. The bytes type is used for raw byte data. This means Python 3 "just works" with text from all over the world.

# Python 3
emoji = "😊"
print(len(emoji)) # Output: 1 (Correct, it's one character)

# Python 2
# emoji = u"😊" # You had to remember to use the 'u' prefix
# print len(emoji) # Would often cause errors depending on the environment

xrange() is Gone

In Python 2, xrange() was used to create a "lazy" range object that didn't store all numbers in memory at once, which was great for very large loops. range() would create a full list in memory.

In Python 3, range() was rewritten to have the same memory-efficient behavior as xrange(), so xrange() was removed to simplify the language.

Practical Advice: What Should You Do?

If You Are a Beginner

Learn Python 3. Full stop. You will avoid all the confusion of legacy quirks and learn the modern, "correct" way of doing things. All modern tutorials, courses, and documentation are for Python 3. You will have access to all the latest libraries and a much larger community for support.

If You Are Maintaining Old Python 2 Code

If you inherit a large codebase written in Python 2, you have a few options:

• Port the Code: The best long-term solution is to update the code to Python 3. Tools like 2to3 can automate a lot of the conversion, but it will still require manual review and testing to fix logic errors (especially from integer division).
• Keep it on Python 2 (with caution): You can continue to maintain the code on Python 2, but you must understand that it is a security risk. You will not receive any security updates, and you will be unable to use new libraries. This is only a viable option for a short-term transition period.
• Use a Compatibility Layer: Libraries like six or future can help you write code that runs on both Python 2 and 3. This can be useful during a gradual migration but is not a permanent solution.

If You Are Choosing a Technology for a New Project

Choose Python 3. There is no reason to start a new project in Python 2. You will be locking yourself out of the future of the Python ecosystem. All major frameworks (Django, Flask, FastAPI), data science tools (Pandas, NumPy, TensorFlow, PyTorch), and cloud services have fully embraced Python 3.

Conclusion

Think of it like this: Python 2 is a classic car. It's interesting to look at and understand its history, but you wouldn't want to drive it every day or rely on it for a long road trip. Python 3 is the modern, safe, and reliable vehicle that will take you where you need to go.

For any new development, Python 3 is the only logical choice.