1. CS3430:Python & Perl
Lecture 01
Department of Computer Science
Utah State University

2. Outline
●
●
●
●
●
●
●
Course Overview
Python Overview: History, Features, Strengths,
Weaknesses
Installing Python on Windows/Linux/Mac OS
Python 2.X or Python 3.X
Playing with Python through its Interpreter
Comments, Booleans, Variables, Lists, Strings, Tuples
Built-in Functions and Methods

3. Schedule & Workload
●
Python – 10 weeks
●
Perl – 5 weeks
●
Two exams (dates in the syllabus)
Midterm 1: Python
 Midterm 2: Python & Perl (mostly Perl)
Regular weekly coding assignments

●
●
Final project (last 4 weeks)

4. Texts

5. Python Text 1

6. Python Text 2
Download free PDF version at http://greenteapress.com/thinkpython/thinkpython.html

7. Perl Text

8. Logistics
●
●
●
No emails on weekends please
Both exams will be online; you can take them anywhere you
want
Please turn off your cell phones in class

9. Class Attendance
●
●
●
Class attendance is completely optional
I know students who show up for every class and get C's and
D's; I know students who show up for no class or just a few
classes and ace all assignments, projects, and exams
Do not waste your time showing up for class to do homework
for other classes, read email, browse the web, chat with
friends, play games, etc

10. Python Overview
History, Features, Strengths, Weaknesses

11. History
●
●
●
●
●
Python is a general purpose programming language
Python is considered a scripting language but it is possible and practical to develop systems and executables
Python was created by Guido van Rossum in the 1990's.
Guido van Rossum is sometimes referred to as “Python's
Benevolent Dictator for Life” (BDFL).
The name “Python” comes from “Monty Python's Flying
Circus.”

12. Features
●
●
●
●
●
Dynamic typing
Automatic memory management (aka garbage
collection)
Support for large applications (system programming)
Numerous built-in tools and libraries
Numerous 3rd party tools and libraries

13. Strengths
●
Free
●
Portable
●
Easy to learn and use
●
Mixable
C/C++ programs can call Python programs
 Python can link to C/C++ libraries
Supports object-oriented programming

●

14. Weakness
●
●
Python programs can run slower than their C/C++
counterparts
If and when this happens, you have to ask yourselves two
questions:


Do I really need this for my particular application? In
many cases, no!
Can I port the bottleneck to C/C++? In many cases, yes!

15. Why not C++ for Everything?
Scripting languages represent a different set of tradeoffs
than system programming languages. They give up
execution speed and strength of typing relative to system
programming languages but provide significantly higher
programmer productivity and software reuse.
John K. Ousterhout, Creator of Tcl
“Scripting: Higher Level Programming for the 21st
Century” IEEE Computer magazine, March 1998
Full article: http://www.tcl.tk/doc/scripting.html

16. Python 2.X or Python 3.X

17. Python 2 or Python 3?
●
●
●
●
Python 2.X is the status quo, Python 3.x is the shiny new
thing
Python 3.X is the newest branch of Python and the
intended future of the language
However, the broader Python 2.X ecosystem has amassed
a significant amount of quality software over the years
Insightful article on Python 2 vs. Python 3 on
www.python.org

18. Python 2 or Python 3?
●
●
●
While Python 3.X is the same language, it is not
backward compatible to Python 2.X
The downside of breaking backwards compatibility in
3.X is that a lot of that software does not work on 3.X
yet; this transition will take time
Python 3.X has relatively limited library support; many
Linux distributions and Macs ship with 2.X

19. Reasons to Prefer Python 2 over Python 3 (For Now)
1. If you are deploying to an environment you do not control.
2. If you use a third party package that does not have a released
Python 3 version.
3. If you want to use a third-party tool such as Python Image
Library (PIL), Twisted (for networking), Django (for building
websites), or py2exe (for packaging your application for Windows
users)

20. Reasons to Prefer Python 2 over Python 3 (For Now)
4. A lot of documentation (including examples) on the web and in
reference books will be for Python 2 for the near future
5. Most of us are inclined to seek help online. The Python regulars
are typically seasoned developers who rely on legacy software, most
of which has not been ported to Python 3 yet. As a result, they might
not be able to help you with Python issues
6. It is always better to study the tool you are transitioning to and
wait until it becomes accepted by the broader community.

21. Installing Python on
Windows/Linux/Mac OS

22. What We Will Use
●
●
●
We will use Python 2.7 in this class
If you are a Linux user, note that many versions of
Linux ship with 2.6.X
If you are a Mac user, note that most Macs still ship
with 2.6.X; check for the Mac distribution of 2.7

23. Installing Python
●
●
●
●
www.python.org is the site for everything that is Python.
On Windows, I use IDLE for execution and debugging and
IDLE or Emacs for editing
On Linux (Ubuntu), I use command line interpreters for
execution and debugging and Emacs for editing.
You may want to play with several choices and choose what
you like best. It does not really matter which IDE you use.
You will submit only the Python source files (.py) in your
assignments

24. Playing with Python

25. Python Interpreter
●
●
●
Python Interpreter is an interactive program that allows you to
work with Python source code without having to create, edit,
save, and compile source files
As you read online materials or test, I suggest that you keep
the Python interpreter window running and try code snippets
right away
Most Python IDEs make the Python interpreter easily
available

26. Python Interpreter
>>> print 'Hello, Python!'
Hello, Python!
>>> “Hello, Python!”
Hello, Python!
>>> 5
5
>>> 5 + 10
15

27. Comments
●
●
The hash mark character (#) introduces comments
# can appear at the beginning of a line or in the middle of a
line
●
The characters after # and upto n are part of a comment
●
Examples:


# This is a comment
x + y # add x and y

28. Variables
●
●
●
●
Since Python is a dynamically typed language, the types of
variables are not explicitly declared
A variable can refer to an object of any legal Python type
The type of a variable is determined at run time through the
operations that are applied to the variable's value
Examples:




>>> x = 1 # the value of x is integer 1
>>> x + 1 # is OK
>>> x + 'bar' # is ERROR

29. ●
●
Python has two Boolean values: True and False
Booleans
All Python values can be represented as Booleans: all numbers except
0 are True; all non-empty containers are True; all empty containers
are False; For example:

>>> file_ready = False

>>> bool(file_ready)
False

>>> bool(1)
True

>>> bool([])

False

30. Factory Functions
●
Numeric types have factory functions that convert from one type to
another; For example:

>>> int('12')
12

>>> int(12.5)
12

>>> int('12.1')
ERROR

>>> float('12.1')
12.1

31. Lists, Strings, Tuples, Iterables
●
Lists: [1, 2, 'a']
●
Strings: 'Python', “Python”, “Djangon”
●
Tuples: ('a', 1), (1, 2)
●
Lists are mutable (support assignment)
●
Strings and tuples are immutable
●
Iterables are any objects that can be iterated through one item
at a time

32. Reading & References
●
●
●
www.python.org.
Ch. 01, M. L. HetLand. Beginning Python From Novice to
nd
Professional, ,2 Ed., APRESS.
H. Abelson and J. Sussman. Structure and Interpretation of
Computer Programs, 2nd Ed., MIT Press.