1. What is a scripting language? What is Python?
Scripting with Python
What is a scripting language?
What is Python?

2. Scripting Languages
Originally, a script was a file containing a sequence of commands that needed to be executed
Control structures were added to make it possible to do more with scripts

3. Characteristics of Scripting Languages
Generally interpreted
Dynamic typing - no declarations
Make text processing easy
Often provide pattern matching for strings
Provide file and directory manipulation
Make it easy to do things quickly

4. Basic Scripting Languages
Unix and Linux come with shell programs which are programmable sh
bash
ksh
csh
DOS had BAT files

5. Scripting in Other Environments
Even with a GUI operating system, it is still useful to be able to automate repetitive tasks
Windows still has bat files
Mac OS has AppleScript
Some applications have a scripting language built into them
Microsoft applications have Visual Basic for Applications (VBA)‏
Hypercard (Apple) had HyperTalk

6. Other Scripting Languages
Other scripting languages were developed to provide increased capability
sed -- adapted from the UNIX ed editor in 1977
AWK -- created by Ajo, Wienberger and Kernighan in 1977
Tcl -- an extensible scripting language written by John Ousterhout in 1987
Perl -- created by Larry Wall in 1986
Python-- created in 1989 by Guido van Rossum
Ruby -- created in 1993 by Yukihiro Matsumoto

7. Scripting and the Web
More recently, a number of scripting languages have been developed for use with web browsers
PHP
JavaScript
ASP (part of Microsoft .NET framework)‏

8. Scripting on onyx the shell languages sed awk perl python ruby tcl
javascript
php

9. Python An object-oriented scripting language
Portable (written in ANSI C)‏
Powerful - see next slide
Mixable - can be used in conjunction with other languages
Easy to use
Easy to learn

10. The Power of Python dynamic typing built-in objects built-in tools
built-in libraries
garbage collection
modular

11. Running Python code
Run the python interpreter and type the commands in interactively
Call the interpreter with the name of the script
python progName
Type the program name of an executable script file
chmod +x script
./script
The first line of the script should be
#!/usr/bin/python

12. Hello World #!/usr/bin/python import sys
sys.stdout.write("Hello world!\n")‏

13. Python Program Structure
A python program is composed of modules
A python module is composed of statements
statements are terminated by a newline unless the last character is a \ or there is an unclosed (. [ or {
Put two statements on a line with a ; between
Statements create and process objects

14. Python Built-in Types Numbers (immutable)‏
Sequences - indexing, slicing, concatenation
Strings (immutable)‏
Lists (mutable)‏
Tuples (immutable)‏
Mapping - indexing by key
Dictionaries (mutable)‏
Files

15. Numbers
Numeric types
integers - a C long
long integer - arbitrary number of digits
floating point - C double
complex
Standard arithmetic, comparison, bitwise operators plus ** (exponentiation)‏
Built-in functions : pow, abs, …
Modules : rand, math, cmath

16. Sequences
Strings : 'abc', "def", """triple-qouted for multi-line strings"""
Lists : [1, 2, 4]
Tuples : (1, 2, 3)‏

17. Sequence Operations concatenation with + indexing with [ ]
slicing (substring) with [ : ]
len( s) to get length
% for formatting : fmtString % string
* for repeating
in for membership : 'a' in str

18. Strings Immutable, ordered sequences of characters
Supports all sequence operations (see strings.py)‏
string module provides other functions
re module supports pattern matching

19. string module Names must be qualified with the module name (string. )‏
upper(str), lower(str) - returns a string
find( str, substr) returns index of substr
split( str, delimStr=" ") returns list of string
join( strList, separator) returns a string

20. String class
As objects, strings have may of the same methods that the string module contains
Qualify the methods with the name of the string

21. Lists Ordered collection of arbitrary objects
arrays of object references
mutable
variable length
nestable
Representation : [0, 1, 2, 3]
list methods modify the list (append, sort)‏
see lists.py

22. Tuples Ordered sequence of arbitrary objects Immutable Fixed length
Arrays of object references
Representation : (1, 2, 3)‏
Like lists except no mutations allowed

23. Dictionary Unordered collection of arbitrary objects
Element access by key, not index (hash table)‏
Variable length, mutable
nestable
Representation : {'spam' : 2, 'eggs' : 3}
see dict.py

24. Dictionary operations
element access : d[key]
insert, update : d[key] = 'new'
remove : del d [key]
length: len(d)‏
methods
has_key( str)‏
keys() returns list of keys
values() returns list of values

25. Boolean Expressions Expression truth values
0, "", [], {}, 0.0, None are all false
everything else is true
Comparison operators: < <= == != >= >
return True and False (1 and 0)‏
Python allows a < b < c
Boolean operators: and or not
return an object which is true or false

26. Comparison == checks for value equivalence
is checks for object equivalence
< <= > >= do element by element comparison
think of how strings are compared in Java

27. Python Statements Assignment Function calls print if/elif/else
for/else
while/else
Def, return
import, from
break, continue
pass - no-op
try-except-finally
raise (exception)‏
class
global
del - delete objects
exec

28. Assignment Variable names follow the same rules as in C
Names are created when they are first assigned
Names must be assigned before they can be referenced
Assignment creates an object reference
Associativity is right to left

29. Assignment examples spam = 'spam' spam, ham = 'yum', 'YUM'
list = [1, 2, 3]
tuple = ('a', 'b', 'c')‏
d = {1 : 'one', 2 : 'two', 3 : three}

30. Blocks Blocks in python are started by a compound statement
header :
stmt1 …
laststmt
Blocks terminate when the indentation level is reduced

31. if Syntax else and elif are optional Can have arbitrary number of elif
if test1:
block1
elif test2:
block2
else:
elseblock
else and elif are optional
Can have arbitrary number of elif

32. while Syntax while test: loopbody else: nobreakaction
Optional else part is executed if loop exits without a break
break and continue work as in Java
pass is a null statement used for empty body

33. for for loop is a sequence iterator works on strings, lists, tuples
range is a function that generates a list of numbers
for var in seq
loopbody
else:
nobreakaction

34. Functions Define with def fun(p1, p2): return p1 + p2 Call with
Function without a return statement returns None
Names are local unless declared global
Variables are references
assigning to a parameter does not change the caller
changing a mutable object does change the caller

35. Scope Python has three scopes
local (in function)‏
global (in module)‏
built-in
Nested functions do not have nested scope

36. os Module Provides a portable way to do OS- dependent operations
manipulating files and directories
listdir( path)
mkdir( path)
chmod( path, mode)
process management
fork, exec, kill
system( command)
system information