What is a program

The definition of a program at its most basic is a sequence of Python statements that have been crafted to do something. Even our simple hello.py script is a program. It is a one-line program and is not particularly useful, but in the strictest definition, it is a Python program.

It might be easiest to understand what a program is by thinking about a problem that a program might be built to solve, and then looking at a program that would solve that problem.

Lets say you are doing Social Computing research on Facebook posts and you are interested in the most frequently used word in a series of posts. You could print out the stream of facebook posts and pore over the text looking for the most common word, but that would take a long time and be very mistake prone. You would be smart to write a Python program to handle the task quickly and accurately so you can spend the weekend doing something fun.

For example look at the following text about a clown and a car. Look at the text and figure out the most common word and how many times it occurs. the clown ran after the car and the car ran into the tent and the tent fell down on the clown and the car

Then imagine that you are doing this task looking at millions of lines of text. Frankly it would be quicker for you to learn Python and write a Python program to count the words than it would be to manually scan the words.

The even better news is that I already came up with a simple program to find the

most common word in a text file. I wrote it, tested it, and now I am giving it to

you to use so you can save some time.

name = raw_input('Enter file:')

handle = open(name, 'r')

text = handle.read()

words = text.split()

counts = dict()

for word in words:

counts[word] = counts.get(word,0) + 1

bigcount = None

bigword = None

for word,count in counts.items():

if bigcount is None or count > bigcount:

bigword = word

bigcount = count

print bigword, bigcount

You don’t even need to know Python to use this program. You will need to get through Chapter 10 of this book to fully understand the awesome Python techniques that were used to make the program. You are the end user, you simply use the program and marvel at its cleverness and how it saved you so much manual effort. You simply type the code into a file called words.py and run it or you

download the source code from http://www.pythonlearn.com/code/ and run it.

This is a good example of how Python and the Python language are acting as an intermediary between you (the end-user) and me (the programmer). Python is a way for us to exchange useful instruction sequences (i.e. programs) in a common language that can be used by anyone who installs Python on their computer. So neither of us are talking to Python, instead we are communicating with each other through Python.