Outline

• Outline
• Algorithms
• Numbers
• Variables
• Statements
• User input
• Functions
• Modules
• Saving and executing scripts
• String Basics

Algorithms

What is an algorithm? An algorithm is a set of instructions or a recipe for a computer to carry out.

Numbers

By default, 1 / 2 yields 0 in python. This is integer division.
Solution: from __future__ import division

Variables

What is a variable? A variable is a name that refers to some value (could be a number, a string, a list etc.)

1. Store the value 42 in a variable named foo
   foo = 42

2. Store the value of foo+10 in a variable named bar
   bar = foo + 10

Statements

What is the difference between an expression and a statement? An expression is something, and a statement does something.

User input

1. Ask the user to input a number, and store it as the variable foo
   foo = input("enter a number: ")

2. What is the value of foo now?
   

3. Add foo and bar together
   foo + bar

4. Calculate the average of foo and bar, and save it as a variable named avg
   avg = (foo + bar)/2

Functions

What is a function? A function is a mini-program. It can take several arguments, and returns a value.

Modules

What is a module? Python is easily extensible. Users can easily write programs that extend the basic functionality, and these programs can be used by other programs, by loading them as a module

1. load the math module
   import math

2. Round 35.4 to the nearest integer
   math.round(35.4)

3. Round the quotient of foo and bar down to the nearest integer
   math.floor(foo/bar)

Saving and executing scripts

Script File: hello.py
[language=python] #!/usr/bin/env python # this script prints ’hello, world’, to stdout print "hello, world" Add executable permission:
chmod a+x hello.py
Run the program:
./hello.py

String Basics

• Strings must be enclosed in quotes (double or single)

• Strings can be concatenated using the + operator