Day 1 – Lesson 2
Fundamentals of Programming
Languages
Python Mini-Course
University of Oklahoma
Department of Psychology
1
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Lesson objectives
1. Describe the basic structure of the
Python language
2. Use the IDLE interactive
interpreter
3. Identify three kinds of errors that
occur in programming and
describe how to correct them
2
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Formal languages
 Designed for specific apps
 Ex: mathematical notation
 Have strict rules for syntax
 3 + 3 = 6
 3+ = 3$6 (bad syntax)
 Are literal and unambiguous
 Structure is critical
3
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Programming languages
 Formal languages that are
designed to express computations
and algorithms
 Low level
 One step removed from the 1’s and 0’s
used by the computer
 High level
 More human-friendly languages
4
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Translating
 High level language must be
translated into low level language
by either:
 Interpreter (at run-time)
 Compiler (creates a file containing
executable object code)
 Python is an interpreted language
5
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Starting IDLE
6
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Programs
 Programs are sequences of
instructions
 Input
 Output
 Math and data manipulation
 Conditional execution
 Repetition
7
Python Mini-Course: Day 1 - Lesson 2
4/5/09
The “Hello, World” program
8
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Scripts
 A script is a file that contains a
program in a high-level
language for an interpreter
 Python scripts are text files
ending in .py
 Create HelloWorld.py
9
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Executing scripts
 Python scripts are run in a
“shell”
 This can be IDLE, a terminal shell
(OS X, Linux, Unix), or a
command prompt window (MS
Windows)
 Run HelloWorld.py in IDLE
10
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Debugging
 You will make mistakes while
programming!
 These mistakes are called
“bugs” and the process of
tracking them down and
eliminating them is debugging
11
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Syntax Errors
 All programming languages are
picky about syntax
 Try this:
 1 + 2) + 3
 Syntax errors can be identified
using automated code checking
(color coding) and by error
messages
12
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Runtime errors
 Errors that occur when
program is running
 Also called “exceptions”
 Ex: runtime.py
 Identified by testing the
program (this includes using
test modules)
13
Python Mini-Course: Day 1 - Lesson 2
4/5/09
Semantic or logical error
 Program runs (and does
exactly what you told it to do)
 But you made a mistake in the
design or implementation
 Identified by case-based
testing
14
Python Mini-Course: Day 1 - Lesson 2
4/5/09