What is the difference between Python 2 and Python 3?

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Jayant Kumar · Accepted Answer

Table of Contants
Introduction
Python 2 and Python 3 are two major versions of the Python programming language, with Python 3 being the latest and recommended version. While Python 2 has been widely used for many years, Python 3 introduces several improvements and changes that make it a more robust and modern language. This guide explores the key differences between Python 2 and Python 3.
Key Differences Between Python 2 and Python 3
1. Print Statement vs. Print Function

Python 2: print is used as a statement.
print "Hello, World!"

Python 3: print is used as a function and requires parentheses.
print("Hello, World!")

2. Integer Division

Python 2: Division between two integers performs integer division by default.
result = 5 / 2  # Output: 2

Python 3: Division between two integers produces a float. Use // for integer division.
result = 5 / 2   # Output: 2.5
result_int = 5 // 2  # Output: 2

3. Unicode Support

Python 2: Strings are ASCII by default. Unicode support is provided through a separate unicode type.
u_string = u"Hello, World!"

Python 3: All strings are Unicode by default, which simplifies handling text data.
string = "Hello, World!"

4. Iterators and Generators

Python 2: Functions like range() return lists, which can be memory-intensive for large ranges.
numbers = range(5)  # Returns a list [0, 1, 2, 3, 4]

Python 3: Functions like range() return iterators, which are more memory efficient.
numbers = range(5)  # Returns an iterator

5. Error Handling

Python 2: except blocks use comma syntax.
try:
    # code
except IOError, e:
    # handle IOError

Python 3: except blocks use as syntax for catching exceptions.
try:
    # code
except IOError as e:
    # handle IOError

6. Dictionary Iterators

Python 2: Dictionary methods like dict.keys(), dict.items(), and dict.values() return lists.
d = {'a': 1, 'b': 2}
keys = d.keys()  # Returns a list

Python 3: Dictionary methods return view objects, which are more memory efficient.
d = {'a': 1, 'b': 2}
keys = d.keys()  # Returns a view object

7. Input Handling

Python 2: raw_input() is used for reading user input as a string, while input() evaluates the input as Python code.
name = raw_input("Enter your name: ")

Python 3: input() reads user input as a string. Use eval() if evaluation is needed.
name = input("Enter your name: ")

Best Practices for Transitioning from Python 2 to Python 3

Use **__future__** Imports: Start by using __future__ imports to bring Python 3 features into Python 2 code.
from __future__ import print_function

Employ Compatibility Libraries: Use libraries like six or future to write code compatible with both Python 2 and Python 3.

Run **2to3** Tool: Use the 2to3 tool to automatically convert Python 2 code to Python 3.
2to3 -w your_script.py

Test Thoroughly: Ensure extensive testing to verify that the code works correctly in Python 3. Use continuous integration tools to automate testing.

Upgrade Dependencies: Make sure all third-party libraries and dependencies are compatible with Python 3.

Conclusion
The transition from Python 2 to Python 3 involves several significant changes, including differences in syntax, integer division, and Unicode support. While Python 2 has been widely used, Python 3 offers enhanced features and improvements that make it a more modern and robust language. By following best practices for transitioning and leveraging Python 3's capabilities, developers can ensure that their codebase remains current and efficient.

What is the difference between Python 2 and Python 3?

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