A Byte of Python

The interpreter prompt

We can use the Python interpreter to run our programs as and when we write the code.

First, we have to open a command line. Linux/BSD/Mac users can open up a shell emulator of their choice such as konsole or gnome-terminal. Windows users can open up the DOS prompt by running Start -> Run, enter the word cmd (in Windows XP) or command (in older versions) and press the enter key.

Now, we need to run the Python interpreter. In the command line, enter the word python and press the enter key. You should see something like this:

C:\Documents and Settings\Admin>python 
ActivePython 2.4 Build 244 (ActiveState Corp.) based on 
Python 2.4 (#60, Feb  9 2005, 19:03:27) [MSC v.1310 32 bit (Intel)] on win32 
Type "help", "copyright", "credits" or "license" for more information. 
>>>

Notice that >>> is the prompt waiting for you to enter your Python code.

Now enter print 'Hello World' followed by enter key. You should now see the words Hello World printed on your screen by Python just like you asked it to.

C:\Documents and Settings\Admin>python 
ActivePython 2.4 Build 244 (ActiveState Corp.) based on 
Python 2.4 (#60, Feb  9 2005, 19:03:27) [MSC v.1310 32 bit (Intel)] on win32 
Type "help", "copyright", "credits" or "license" for more information. 
>>> print 'Hello World' 
Hello World

Now wasn't that easy? :-)

If you get an error like this:

C:\Documents and Settings\Admin>python 
ActivePython 2.4 Build 244 (ActiveState Corp.) based on 
Python 2.4 (#60, Feb  9 2005, 19:03:27) [MSC v.1310 32 bit (Intel)] on win32 
Type "help", "copyright", "credits" or "license" for more information. 
>>>   print 'Hello World' 
  File "<stdin>", line 1 
    print 'Hello World' 
    ^ 
SyntaxError: invalid syntax 
>>> 

it means that you entered some spaces before the word print. You will soon learn why Python behaves this way. For now, type the same line again without having any spaces or tabs before the print word and it should work.

Notice that Python gives you the 'output' of the program you entered almost immediately. Yes, what you entered is a real and complete Python program.

print is a statement used to, unsurprisingly, print anything that is supplied to it. In this case, we are supplying the text 'Hello World' and the print statement promptly prints it to the screen.

How to quit the Python prompt

If you are using Linux/BSD/Mac, press Ctrl-d.

If you are using Windows, press Ctrl-z followed by enter key.