Python Programming Language is one of the most popular programming languages in the world. Python took a major leap when it launched its version 3.x in year 2008. There are significant performance increases along with other enhancements. At present, the latest stable version of Python is 3.13. Let’s now see some of the major differences:-
Print(): One of the prominent changes which has happened in python 3 is a change in the print method. In python 3, the print keyword in Python 2.x is replaced by the print() function. Note: parentheses work in Python 2 if space is added after the print keyword because then the interpreter evaluates it as an expression. Even libraries made for python2 is not compatible with python 3
#Python 2
# in python2 print is a keyword, print() often works with python2 because it internally converts it to print ()
print "you need to know it, in case you need it in future"
#Python 3
print("you need to know it, in case you need it in future")
Division: In python 2.x, when 2 integers are divided the result is always an integer. Whereas, in python 3.x when 2 integers are divided the result is a float value.
#Python 2 5/2 #output = 2 #Python 3 5/2 #output = 2.5
Xrange: In pythn 2.x, range() and xrange() functions are available. Range returns list of elements & xrange() returns an iterable object. But in python 3.x, xrange() and range has been merged into one .i.e. range().
#Python 2 range(10) #output [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] xrange(10) #output xrange(10) #Python 3 range(10) #output range(0,10)
Error Handling: In python 3.x, ‘as’ keyword is required in try-except block and this is mandatory. If as is not mentioned, the code will throw an error.
#Raising Exception in Python 2
>>> raise Exception, "This is exception"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
Exception: This is exception
>>> raise Exception("this is exception")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
Exception: this is exception
#Raising exception in Python 3
>>> raise Exception("this is exception")
Traceback (most recent call last):
File "<python-input-1>", line 1, in <module>
raise Exception("this is exception")
Exception: this is exception
__future__ module: 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.
List Comprehension Loop Variables: In python 2, if loop variables and global variables are of same name, the values of global variables changes after the execution of list comprehension. This problem was solved in python 3.x
#python 2 Example (variables leakage)
x = 100
print("Before:", x)
# List comprehension uses the same variable name
squares = [x*x for x in range(5)]
print("Squares:", squares)
print("After:", x) # x is now 4 (last value from list comprehension)
################
#Python 3 Example (No Variables leakage)
x = 100
print("Before:", x)
squares = [x*x for x in range(5)]
print("Squares:", squares)
print("After:", x)
#Outputs below:
Before: 100
Squares: [0, 1, 4, 9, 16]
After: 100
Unicode Strings: In python 2, the strings were saved as ASCII but in python 3.x strings are stored by default as unicode. This means that in Python 3.x, you can use characters from any language in your code without having to encode or decode them. In Python 2.x, you can use the u"Hello World" syntax to create Unicode strings, while in Python 3.x, you can simply use "Hello World". The u prefix is not necessary in Python 3.x.
Python 3.x is now used everywhere and python 2.x is very outdated, its always better to know some of the major differences.
The codes (if any) mentioned in this post can be downloaded from github.com. Share the post with someone you think can benefit from the information
