README.md

Python 2 versus Python 3

The most prominent differences between Python 2 and Python 3 are presented here. Thankfully, they're relatively easy to get used to. If you're curious about the other differences, Sebastian Raschka's article on the topic lays them out nicely.

Using print

In Python 2, print is a statement, while in Python 3, print is a function. Practically, this means that in Python 2 you can do things like:

# using Python 2
print "Hello, World!"
print "LaunchCode", "is great"

Output:

Hello, World!
LaunchCode is great

In Python 3, the equivalent code would be

# using Python 3
print("Hello, World!")
print("LaunchCode", "is great")

For most intents and purposes, you can see that Python 2 print statements don't use parentheses, but Python 3 print statements do. That said, you can do the following in Python 2:

# using Python 2
print("Hello, World!")
print("LaunchCode", "is great")

with output:

Hello, World!
(LaunchCode, is great)

Hence, Python 2 will accept print statements with parentheses, but with potentially unexpected output. Conversely, if you try to use print without parentheses in Python 3, you'll get a syntax error.

# using Python 3
print "please print me"

Output:

  File "<stdin>", line 1
    print "please print me"
                          ^
SyntaxError: Missing parentheses in call to 'print'

Prompting for input

In Python 3, you've used the input function to prompt for user input.

# using Python 3
name = input("What's your name? ") # name is a string
age = input("How old are you? ") # age is a string

In Python 2, to get the same behavior we have to use the raw_input function.

# using Python 2
name = raw_input("What's your name? ") # name is a string
age = raw_input("How old are you? ") # age is a string

input is available as a function in Python 2, but it behaves differently than in Python 3. For more details, see the article linked above.