Python Rules

1
Python Rules

• A Quick Introduction to Python

2
Python What?

• Python is a portable, open source object-oriented
  scripting language
• Scripting Language?
• Rapid, flexible application development
• Flexible and rapid because there is no compile
  phase and very loose data typing
• Estimated 500,000 to 1 million users as of 2003
  and over a decade old
• www.python.org

3
Python Uses

• Systems Programming (shell tools)
• GUI Programming
• Internet Scripting (i.e. CGI, XML)
• Component Integration (glue code)
• Database Programming
• Rapid Prototyping
• Numeric Programming
• Gaming

4
Disadvantages

• Interpreted and therefore execution speed can be
  relatively slow
• Loose typing and lack of a compile phase can be
  the result of troubling runtime errors

5
Interactive Coding

• Pythons interactive command line is a great
  place to experiment with Python and test your
  code
• print Hello World!Hello world
• print 2 8256
• lumberjack okaylumberjackokay

6
Python Scripts

• A text file that contains several Python
  commands, and has a .py extension
• Can be executed using python myscript.py
• Since Python scripts are just text, they are
  portable and can be run on any platform that has
  Python

7
IDLE

• IDLE is an IDE that comes with the standard
  Python install
• IDLE has
• An interactive prompt with syntax highlighting
• An editor with syntax highlighting
• A code syntax checker
• A debugger
• A graphical way to run your Python scripts

8
Variables

• No need to declare a variable
• A variables type can change
• The possible built-in types are
• Numbers 3.141, 1234
• Strings Jim, Toms
• Lists 1, 2, 3, 4, 5
• Dictionaries food spam, taste yum
• Tuples (a, 1, b)
• Files text open(myfile, r).read()

9
Strings

• len(abc)3
• abc defabcdef
• print -10----------
• s spams0, s-2 comma gives us a
  2-tuple(s, a)
• Strings are immutable
• s0 x error
• s13, s1, s-1
• (pa, pam, spa)

10
More Strings

• Formatting
• print i s i you (a, spam, 4)1 spam
  4 you
• Methods
• s.capitalize()
• s.replace(old, new)
• sspammys.replace(mm,
  xx)sspaxxy
• s.find(sub)
• s xxxxSPAMxxxxwhere
  s.find(SPAM)where4

11
Lists

• mylist 1, 2, 3len(mylist)3
• mylist 4, 5, 61, 2, 3, 4, 5, 6
• Lists are mutable
• mylist1 hellomylist1, hello, 3,
  4, 5, 6

12
More Lists

• mylist spam, Spam, SPAM!mylist0
  2spam, Spam
• mylist02 eat, moremylist
• eat, more, SPAM!
• Methods
• mylist.append(hello)
• mylist.extend(1, 2, hello)
• mylist.pop()
• del mylist1
• mylist.reverse()

13
Dictionaries

• ages Jon 35, Sally 36agesJon
  35
• agesSally 36, Jon 35
• len(ages)2
• agesJon 20agesJon20

14
More Dictionaries

• Methods
• ages Jon 35, Sally 36d2.keys()
  Jon, Sally
• d2.values()35, 36
• d2.has_key(Sally)1

15
Block Delimiters

• No Special Block Characters
• Blocks are specified using indentation
• If different indentation is used a syntax error
  will occur
• Example
• does compileif x print hello print
  goodbye
• does not compileif y print yes print
  no

16
If/Else

• x 10
• if x 10 print hello... elif x
  20 print goodbye print
  Charlie else print jumphello
  

17
While Loops

• x spamwhile x print x x
  x1
• spam pam am m

18
For Loops

• for var in list/string
• Example
• s lhu
• for c in s print clhu
• Use the range function for counter loops
• range(3)0, 1, 2
• for i in range(3) print I012

19
Functions

• Unlike compiled languages, you have to execute
  code in order to create a function
• Once the code executes, it creates a new function
  object, and assigns a name to the object
• You can use the reference to call the function

20
Functions (cont.)

• Syntax def (arg1, arg2, argN)
  
• Example
• def intersect(seq1, seq2) res
  for x in seq1 if x in seq2
  res.append(x) return res
• s1 SPAMs2 SCAMintersect(s1,
  s2)
• S, A, M

21
More I Say!

• What I have not covered
• Lots!
• Python makes it possible to create and import
  modules for code reuse and good software design
• Python is object-oriented and modules can contain
  classes
• Python has a large, full-featured standard
  library that includes
• GUI tools
• Database tools
• Internet programming tools
• Regular expressions
• And a lot more
• Download Python now for free, install it, and
  have fun!