Important differences between Python 2.x and Python 3.x with examples

Last Updated : 06 Sep, 2023

In this article, we will see some important differences between Python 2.x and Python 3.x with the help of some examples.

Differences between Python 2.x and Python 3.x

Here, we will see the differences in the following libraries and modules:

Python Division operator

If we are porting our code or executing python 3.x code in python 2.x, it can be dangerous if integer division changes go unnoticed (since it doesn’t raise any error). It is preferred to use the floating value (like 7.0/5 or 7/5.0) to get the expected result when porting our code. For more information about this you can refer to Division Operator in Python.

Python3

print(7 / 5 ) print(-7 / 5) ''' Output in Python 2.x 1 -2 Output in Python 3.x : 1.4 -1.4 '''

Print Function in Python

This is the most well-known change. In this, the print keyword in Python 2.x is replaced by the print() function in Python 3.x. However, parentheses work in Python 2 if space is added after the print keyword because the interpreter evaluates it as an expression. You can refer to Print Single Multiple Variable Python for more info about this topic.
In this example, we can see, if we don't use parentheses in python 2.x then there is no issue but if we don't use parentheses in python 3.x, we get SyntaxError.

Python3

print 'Hello, Geeks'      # Python 3.x doesn't support  print('Hope You like these facts')  '''  Output in Python 2.x :  Hello, Geeks  Hope You like these facts   Output in Python 3.x :  File "a.py", line 1      print 'Hello, Geeks'                         ^  SyntaxError: invalid syntax  '''

Unicode In Python

In Python 2, an implicit str type is ASCII. But in Python 3.x implicit str type is Unicode. In this example, difference is shown between both the version of Python with the help of code and also the output in Python comments.

Python3

print(type('default string '))  print(type(b'string with b '))   '''  Output in Python 2.x (Bytes is same as str)  <type 'str'>  <type 'str'>   Output in Python 3.x (Bytes and str are different)  <class 'str'>  <class 'bytes'>  '''

Python 2.x also supports Unicode

Python3

print(type('default string '))  print(type(u'string with b '))  '''  Output in Python 2.x (Unicode and str are different)  <type 'str'>  <type 'unicode'>     Output in Python 3.x (Unicode and str are same)  <class 'str'>  <class 'str'>  '''

xrange vs range() in both versions

xrange() of Python 2.x doesn't exist in Python 3.x. In Python 2.x, range returns a list i.e. range(3) returns [0, 1, 2] while xrange returns a xrange object i. e., xrange(3) returns iterator object which works similar to Java iterator and generates number when needed.
If we need to iterate over the same sequence multiple times, we prefer range() as range provides a static list. xrange() reconstructs the sequence every time. xrange() doesn't support slices and other list methods. The advantage of xrange() is, it saves memory when the task is to iterate over a large range.
In Python 3.x, the range function now does what xrange does in Python 2.x, so to keep our code portable, we might want to stick to using a range instead. So Python 3.x's range function is xrange from Python 2.x. You can refer to this article for more understanding range() vs xrange() in Python.

Python3

for x in xrange(1, 5):      print(x),   for x in range(1, 5):      print(x),  '''  Output in Python 2.x  1 2 3 4 1 2 3 4   Output in Python 3.x  NameError: name 'xrange' is not defined  '''

Error Handling

There is a small change in error handling in both versions. In latest version of Python, ‘as’ keyword is optional.

Python3

try:     trying_to_check_error except NameError, err:   # Would not work in Python 3.x     print err, 'Error Caused'     '''  Output in Python 2.x:  name 'trying_to_check_error' is not defined Error Caused   Output in Python 3.x :  File "a.py", line 3      except NameError, err:                      ^  SyntaxError: invalid syntax  '''

In this example, error handling is shown without the use of "as" keyword.

Python3

try:     trying_to_check_error except NameError as err:     print(err, 'Error Caused')  # code without using as keyword try:     trying_to_check_error      # 'as' is optional in Python 3.10 except NameError:     print('Error Caused')      '''  Output in Python 2.x:  (NameError("name 'trying_to_check_error' is not defined",), 'Error Caused')   Output in Python 3.x :  name 'trying_to_check_error' is not defined Error Caused  '''

future module in Python

This is basically not a difference between the two versions, but a useful thing to mention here. The idea of the __future__ module is to help migrate to Python 3.x.
If we are planning to have Python 3.x support in our 2.x code, we can use _future_ imports in our code.
For example, in the Python 2.x code below, we use Python 3.x's integer division behavior using the __future__ module.

Python3

# In below python 2.x code, division works # same as Python 3.x because we use  __future__ from __future__ import division print(7 / 5) print(-7 / 5)

Output:

1.4  -1.4

Another example where we use brackets in Python 2.x using __future__ module:

Python3

from __future__ import print_function print('GeeksforGeeks')

Output:

GeeksforGeeks

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Article Tags :

Python

Practice Tags :

python

Important differences between Python 2.x and Python 3.x with examples

Differences between Python 2.x and Python 3.x

Python Division operator

Print Function in Python

Unicode In Python

xrange vs range() in both versions

Error Handling

__future__ module in Python

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future module in Python