Python 2 and 3 Differences

Python 2 and 3 are similar but NOT COMPATIBLE! Python 3 does break compatibility. We will be focusing on Python 2.7.13 but will cover 3.6.X along side the entire course.

Print

Python 3 replaced Python 2's print statement with a print function(). While Python 2 will be happy as is or with parantheses... Python 3 will throw an error if the parantheses are not included.

Python 2

print 'Hello World!' # outputs: Hello World!
mystr = 'Goodbye World!'

print mystr # outputs: Goodbye World!
print("This works too") # This works too!

Python 3

print("Hello World!") # Hello World!
mystr = 'Goodbye World!'

print(mystr) # Goodbye World!

Integer Division

Python 2 treats numbers without a decimal as integers, whereas Python 3 will treat them as float if it applies. Python 2 Division with integers truncate the remainder! Setting one number as a real number will yield the correct result.

Python 2

print 3/2 # 1
print 3.0/2 # 1.5

Python 3

print 3/2 # 1.5

Other Major Differences

Unicode:

Python 2 has ASCII str() type, separate unicode() type.. but no byte type.

Python 3 has Unicode (utf-8) str -ings and two byte classes: byte and bytearray.

We will cover both in later lectures.

Input() vs raw_input():

• Python 3 input() always stores userinput as str objects. This is good.
• Python 2 input() on the other hand fully evaluates the code the user gives it. This is dangerous! This gives the full power of Python to the user... and can be used in a malicious way. Instead, we use raw_input() in Python 2... which converts user input to a string.

There are more differences between the two major releases. It's encouraged to look up the differences for better understanding.