Hello world in Python

A "Hello world" program is the customary way to show how to program in a new language. Although the Python's hello world is trivially simple, there is always something to learn from it

Installing Python
Hello world in Python (prior version 3):
The print command
Printing with placeholders
Python 3
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Installing Python

Depending on your operating system, you may need to download Python. Most Linux distributions come with Python as does Mac OS X. Windows does not ship with Python. To test if Python is installed, open a command prompt and enter:

python

If Python is installed you will see the Python interactive interpreter, if not you will receive an error message. To install Python go to http://www.python.org/download/ and download the appropriate file. Follow the instructions to install Python.

Hello world in Python (prior version 3):

Writing a "Hello word" program in Python is trivial:

print "Hello world"

In the interactive interpreter, it looks like this:

This Knol also introduces the print command:

The print command

A print command in Python adds a line feed, so with two prints you will get two lines:

print "Hello"
print "world"

Hello
world

This can be avoided by using a comma (,) at the end:

print "Hello",
print "world"

Hello world

Hello world using variables:

>>> h = "Hello"
>>> w = "world"
>>> print h+' '+w
Hello world

Note that the "+" operation concatenates three strings: Hello, a "space" character and "world".

Printing with placeholders

>>> print "%s %s" %(h,w)
Hello world

By using "%s" you don't have to concatenate strings, just use one string and put a placeholder (the %s) where the variable would go.

Python 3

In Python 3, the print statement is transformed into a function, so a basic hello world, is:

print("Hello world")

There are also some new parameters for the print function: "end" and "sep." The "end" parameter is used to determine what goes at the end of the statement. It defaults to " " (a newline character), exactly like in Python 2.x. The "sep" parameter determines the separator character between the other parameters. It defaults to a space, again like in 2.x. Some examples of utilizing these new parameters:

>>> print("hello","world")
hello world
>>> print("hello","world",sep="separator-text")
## instead of a space, it's "seperator-text" helloseparator-textworld
>>> print("hello","world",end="this is the ending.")
hello worldthis is the ending