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

In this article, we will explore some important differences between Python 2.x and Python 3.x with the help of examples, focusing on the following libraries and modules.

• Division operator
• print function
• Unicode
• xrange
• Error Handling
• _future_ module

1. Python Division operator

• In Python 2.x: dividing two integers performs floor division (discards decimals).
• In Python 3.x: dividing two integers performs true division (keeps decimals).

print 7 / 5             
print -7 / 5            

print(7 / 5)           
print(-7 / 5)           

Output in 2.x:

1
-2

Output in 3.x:

1.4
-1.4

2. Print Function in Python

• In Python 2.x: print is a statement (no brackets needed).
• In Python 3.x: print is a function, so parentheses are required.

# Python 2.x
print 'Hello, Geeks'        # print is a statement
print('This works too')     # works because it's treated like a function call

# Python 3.x
print('Hello, Geeks')       # print is a function (this is the only correct way)

Output in Python 2.x:
Hello, Geeks
This works too

Output in Python 3.x:
Hello, Geeks

3. Unicode In Python

• Python 2.x: Strings are ASCII by default, unicode must be defined separately.
• Python 3.x: Strings are Unicode by default.

print(type('default string'))
print(type(b'string with b'))

Output in Python 2.x:

<type 'str'>
<type 'str'>

Output in Python 3.x:

<class 'str'>
<class 'bytes'>

 4. xrange() vs range()

Python 2.x:

• range() returns a list.
• xrange() returns a generator (saves memory).

Python 3.x:

• xrange() is removed.
• range() behaves like Python 2’s xrange.

# Python 2.x
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

5. Error Handling

• Python 2.x: Uses a comma to bind the exception.
• Python 3.x: Uses as keyword (comma syntax no longer works).

# Python 2.x
try:
    x = not_defined
except NameError, err:
    print err, 'Error Caused'

Output in Python 2.x:

name 'not_defined' is not defined Error Caused

Output in Python 3.x:

SyntaxError: invalid syntax

Correct way (works in both):

try:
x = not_defined

except NameError as err:
print(err, 'Error Caused')

6. __future__ module in Python

__future__ module allows Python 2 code to adopt Python 3 features early, making migration easier.

Example 1: Division behavior

from __future__ import division

print(7 / 5)
print(-7 / 5)

Output (Python 2.x with future import):

1.4 
-1.4

Output (Python 3.x):

1.4
-1.4

Example 2: print as a function

from __future__ import print_function

print('GeeksforGeeks')

Output (Python 2.x with future import):

GeeksforGeeks

Output (Python 3.x with future import):

GeeksforGeeks

Related Articles:

• Python Keywords and Identifiers
• Python Operators