1. Programming in Python

2. Basics What is Python Numeric Types String Types and Variables
Built-in Functions
Data Structures
Conditionals
Loops
Functions
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3. Module 1
What is python
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4. Origin of Python Created by Guido Van Rossum 1986-1991.
Created by Guido Van Rossum
Named after the Monty Python show.
Most stable at version 2.7.x.
Current version is
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5. More About Python Very clear, readable syntax.
Interpreted, Object-Oriented, Interactive
Dynamically typed
Rich standard and 3-rd party library set
Extensible in C/C++/Java
Embeddable C/C++/Java
Portable – Linux / Windows / etc.
Open / GPL-ed
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6. Why would I use it? Easy to learn, yet very powerful
Promotes modularity, code reuse, maintenance.
No compilation step: edit->test->debug cycle is fast.
No seg fault’s, interpreter always throws exceptions.
It is cross platform.
Many large companies using it– also internal Dell support
Free!
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7. Complexity Gauge – Hello World – asm-32
; Hello World for Intel Assembler (MSDOS)
mov ax,cs
mov ds,ax
mov ah,9
mov dx, offset Hello int 21h
xor ax,ax
int 21h
Hello:
db "Hello World!",13,10,"$"
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8. Complexity Gauge – Hello World - Java
// Hello World in Java
class HelloWorld {
static public void main( String args[] ) {
System.out.println( "Hello World!" ); }
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9. Complexity Gauge – Hello World – C#
// Hello World in Microsoft C# ("C-Sharp").
using System;
class HelloWorld {
public static int Main(String[] args) {
Console.WriteLine("Hello, World!");
return 0; }
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10. Complexity Gauge – Hello World – Python
# Hello World in Python
print “Hello World”
Python Motto:
“Simple things simple, complex things possible”
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11. Who uses it? Dell – Test Automation
Google – Many components of Google are written in Python. 1 of 3 std languages (C++, Java).
Yahoo – Yahoo maps, Yahoo Groups (180k lines)
Red Hat / Fedora – The anaconda (Installer) is written in python, both GUI and Text mode. Many other pieces of Red Hat config tools are in Python as well.
NASA – Johnson Space center, standard language for the Integrated Planning System. Efforts underway to migrate older Perl and shell code to Python.
Industrial Light and Magic – Every CG generated was touched by Python somewhere in the process. (Pirates, Transformers, Evan Almighty, Harry Potter)
Games – Civilization IV, Battlefield 2
Rackspace – PHP -> Python for their CORE infrastructure
National Weather Service – Main computer system, 120 sites
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12. What can I use it for? Test automation Deployment automation
System administration task automation
Enabling a high level interface to a C/C++ DLL/.SO
Text processing
Web sites
Etc.
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13. How do I get it? Python - http://www.python.org/download
PyScripter -
Q: The most downloaded version of Python (by OS) is:
A: Win32 (Windows 2K, XP, Vista)!
Q: Why Windows and not Linux?
A: Because Python is already bundled with most Linux distributions including RedHat / SuSe / Ubuntu, etc.
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14. What version? Minimum: Python 2.7.x Python in Linux distributions:
RHEL4 – Python 2.3.4
RHEL5 – Python 2.4.3
RHEL 6 – Python 2.6.6
RHEL 7– Python 2.7.5
Fedora 7 – Python 2.5
SuSE 10 – Python 2.4.2
Windows need to download…
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15. Interactive mode To start python interactively, on lin32, type:
<path>/python2 (or <path>/python25
Python 2.5 (#1, Aug 2006, 12:15:30)
[GCC (Red Hat Linux Rawhide 3.2-4)]
Type “help”, “copyright”, or “license” for more…
>>>
To start python interactively, on win32, type:
<path>\python.exe
Python (#34, Apr , 19:34:33)
[MSC 32 bit (Intel)] on win32]
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16. Lab Install python 2.7.x interpreter (if needed)
Start interpreter, type: 2+2
What was the output?
Type: print “hello world!”
Type: 2+a
Type: 1/0
Using a text editor / IDLE create a file: lab1.py with the above commands.
Run the file with a python interpreter…
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17. Module 2
Numeric types
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18. Overview There are four numeric types:
integers,
long integers,
floating point numbers,
complex numbers
Integers are implemented as longs in C (>=32 bit)
They have *unlimited* precision (till you run out of memory)
Floats are implemented as a C double
Complex numbers are also double (real and imaginary)
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19. Operations Built-in operations: +,-,*,/,% -x
abs(),int(),long(),float()
pow(x,y), x**y
divmod(x,y)=(x/y, x%y)
Modules:
math, cmath modules provide more operations, for eg:
acos(),cos(),exp(),hypot(),log(),sin(),tan()
ceil(),floor()
e, and pi are defined…
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20. Examples 1 print 2+2 # this is a comment4
print 9/4 # integer division returns floor* 2
width = 4
height = 2+2
area = width * height
print area 16
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21. Examples 2 x=y=z=2 # serial assignment print x amount=6.25 tax=8.25
total=amount+(amount*(tax/100))
print round(total, 2)
6.77
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22. Augmented Assignment Operators
AAO’s “simplify” math and *other* object operations.
List of AAOs:
+= = x = x + 5
-= = x = x - 5
*= = x = x * 5
/= = x = x / 5
%= = x = x % 5
Python does not have ++ or --
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23. String type AND VAriables
Module 3
String type AND VAriables
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24. Overview Strings are specified by “string” or ‘string’
Unicode Strings are specified by u”string” or u’string’
Strings support many methods:
capitalize(), expandtabs(), lower(), swapcase(), title(), translate(), upper(), zfill()
replace(), split(), splitlines()
center(), join(), ljust(), rjust(), rstrip(), strip(), lstrip(),
count(), endswith(), find() , index(), rfind(), rindex(), startswith(),
isalnum(), isalpha(), isdigit(), islower(), isspace(), istitle(), isupper()
decode(), encode()
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25. Strings Strings are defined w/ quotes. Either single quotes: ‘ Or
Double quotes: “
A string defined with single quotes DO NOT have any different meaning than strings defined with double quotes.
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26. Triple Quoted Strings
Text formatting can be preserved with Triple quoted strings:
“““Copyright (C) 2007, Dell, Inc.
All Rights Reserved.”””
In a python file, unassigned triple quoted strings can be comments!
Single line comments are signified with the # character.
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27. Examples
Valid? “““ ____ __ __ __ _____ / __| / | / | / | | ___| | | / / | | / / | / | | | |__ | | _ / _ | / / |_/ | | | __| | |_| | / / | | / / | | | |___ \___ / /_/ |_| /_/ |_| |_____|
____ _ _ ____ ____ / _ \ | | / / | ___| | _ \ | | | | | | / / | |__ | |_| | | | | | | | / / | __| | _ / | |_| | | | / / | |___ | | \ \ \____/ |___/ |_____| |_ | \_\
”””
YES
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ASCII ART* -

28. Examples Valid? > s=“hello” # hello > s = # hello
Yes
> s = # hello No
> “““hello”””
> s=“““hello”””
> s=“hello” “““hello”””
Yes
> s=“““he said, ““I can’t”””
> s=“““he said, ““I cant”””””
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29. Concatenation / Repetition
String concatenation operator is: +
String repeat operator is: *
For concatenation string + string:
“AA” + “AA” = “AAAA”
For repetition: string * integer:
“BA” * 2 = “BABA”
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30. Same-line / Newline separators
Newline separator is: \
print \
“hello world”
Same-line separator is: ;
print “hello”; print “world”
hello
world
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31. Suppressing Newline It is possible to suppress new line with: ,
print “hello”, ; print “world” # hello world
NOTE: comma, puts a *space* instead of a \n at end of string.
NOTE: after comma, no operations possible (such as + or *).
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32. Formatting Strings (plain and unicode) can be formatted using %:
format % values
Examples:
“abc = %s” % “def”
‘abc = def’
“my_age = %d” % 102
‘my_age = 102’
“name = %s, age = %d” % (“bob”, 102)
‘name = bob, age = 102’
“name = %s, age = %d” % “bob”, 102
TypeError: not enough arguments for format string
Conversion
Meaning d
signed decimal u
unsigned decimal x
hexadecimal (lowercase) f
floating point (decimal format) s
convert to string
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33. Escape Sequences Escape Sequence Meaning \\ \ \’ ’ \” ” \a ASCII BEL
ASCII BS \f
ASCII FF \n
ASCII LF \r
ASCII CR \t
ASCII tab
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34. Examples Output? > print “hello\rworld” > print “123alog\rcat”
catalog
> print “\a\a\a\n”
Three beeps, cursor..
>print “cat\br”
car
>print “\b|\b/\b-\b\\\b|” |
>print “C:\\dell”
C:\dell
>print “\“Hello\” W”
“Hello” W
>print “\“Hello\’ W”
“Hello’ W
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35. Examples > print “Hello” * 2 > print “Hello” + 2
HelloHello
> print “Hello” + 2
Error
> print “Hello”, 2
Hello 2
> print “Hello”, ; \
print “world”
Hello world
> print “Hello\n” ; \
Hello(blank line)world
Output:
> print “*” * 17; print \
“|\t\t|”; print “|\t\t|”; \ print “*” * 17
A rectangle (for some)
> print “Hello” + ‘world’
Helloworld
> print “Hello” * “2”
Error
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36. Quotes in Quotes
You can use quotes (of the other kind than the ones you are using to define your string) to have quotes in quotes…
‘He said, “Good morning,” to her.’
Question: Is below same as above?
“He said, ‘Good morning,’ to her.”
No!
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37. Naming variables Two rules: Some guidelines:
A variable name can contain only numbers, letters, and underscores.
A variable name CANNOT start with a number.
Some guidelines:
Choose descriptive names.
Be consistent.
Follow conventions / standards.
Keep length in check.
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38. Examples Valid variables? First_name first_name: name_first _name_
yes
first_name: no
name_first
_name_
_!name no
1_2_3
i_2_3
yes
12x
x12_rocket_number_
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39. Module 4
Built-in functions
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40. Overview Some useful built-in functions: Type casting Console I/O
Introspection
list operations
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41. Type casting Type casting: Examples: str(1) chr(97) “2”+“2”
str(obj), chr(x), repr(obj), unicode(object)
int(s), float(s), long(s), coerce(x,y), hex(x), oct(x), ord(c)
Examples:
str(1)
‘1’
chr(97) a
“2”+“2”
“22”
int(“2”)+float(“2”)
4.0
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42. Console I/O print, raw_input examples: print “hello”+“ world”
print “The year is: ”+2004
TypeError: cannot concatenate ‘str’ and ‘int’ objects
print “The year is: ”+str(2004)
The year is: 2004
name=raw_input(“Enter your name: ”)
Enter your name: bob
age=raw_input(“Enter your age: ”)
Enter your age: 102
print “Hello ”+name+“, you are ”+age+“ years old!”
Hello bob, you are 102 years old!
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43. Introspection Introspection functions: Introspection examples: dir()
dir([obj), vars([obj]), globals(), locals(), isinstance(obj, class), type(obj)
Introspection examples:
dir()
[‘__builtins__’, ‘__doc__’, ‘__name__’]
dir(__builtins__)
...
dir(“hello”) …
print isinstance(“hello”, str) 1
print type(“hello”)
<type ‘str’>
n=1
print globals()
… ‘n’: 1
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44. Module 5
DATA Structures
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45. Overview
Python Data Structures be classified into 3 categories of types:
Sequence Types:
strings,
unicode strings,
lists,
tuples.
Mapping Types:
dictionaries
*Set Types:
set,
frozenset.
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46. Sequences: Lists
Lists ~ Arrays / Vectors (they can contain elements of mixed types)
Lists are created using square brackets: [ ]
For list s, items x and t, integer indexes i and j:
s[i] = x # item at location i of s is replaced by x
s[i:j] = t # items i to* j replaced by t
del s[i:j] # delete items i to* j
s.append(x) # add an item x at end of list s
s.count(x) # return numbers of times x is found in s
s.index(x) # return 1st i’th location of x in s
s.insert(i, x) # insert x *AFTER* i
s.pop([i]) # return & delete item in s at i, i default = -1
s.remove(x) # same as s.del(x)
s.reverse() # reverses the items of x in place
s.sort([cmpfnc]) # sorts the items of s in place
# cmpfunc takes two args, returns -, 0, or +
*(not through)
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47. List Examples 1
breakfast = [“eggs”, “milk”, “bacon”, “corissanwich”, 930]
print breakfast
[‘eggs’, ‘milk’, ‘bacon’, “croissanwich”, 930]
print breakfast[0]
eggs
print breakfast[len(breakfast)-1]
930
breakfast[4] = breakfast[4] + 70
print breakfast[4]
1000
del breakfast[4]
IndexError: list index out of range
[‘eggs’, ‘milk’, ‘bacon’, “croissanwich”]
del breakfast[3]
breakfast.append(830) # time for python class
[‘eggs’, ‘milk’, ‘bacon’, 830]
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48. Sequences: Tuples Tuples are like immutable lists.
Tuples are created using parentheses: ( )
Examples:
alphabet = (‘a’, ‘e’, ‘i’, ‘o’, ‘u’, ‘h’, ‘k’, ‘l’, ‘m’, ‘n’, ‘p’, ‘w’)
print alphabet
(‘a’,’e’,’i’,’o’,’u’,’h’,’k’,’l’,’m’,’n’,’p’,’w’)
print alphabet[8]+alphabet[0]+alphabet[4]+alphabet[2]
maui
alphabet.append(b)
AttributeError: ‘tuple’ object has no attribute ‘append’
del alphabet[3]
TypeError: object doesn’t support item deletion
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49. Sequences: Operations
Operations (apply to all sequence types):
x is an item, s and t are sequences, i and j are integers:
x in s # 1 if x is an item in s, otherwise 0
x not in s # 1 if x is not an item in s, otherwise 0
s + t # concatenation of s and t
s * n # n copies of s
s[i] # i’th item in s, indexed from 0
s[i:j] # slice of s from i to j
len(s) # length of s
min(s) # smallest item of s
max(s) # largest item of s
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50. Slice Operator The Slice operation in more detail:
For a sequence s:
s[i:j] # returns indexes k, such that: i <= k < j
Rules:
If i or j is negative, index is relative to end of sequence
i.e. then len(s)+i or len(s)+j is substituted, note: -0 = 0
If i or j > len(s), use len(s)
if i is omitted, use 0, if j is omitted, use len(s)
if i >= to j, the slice is empty; string “”, list [ ], tuple ( )
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51. Sequences: Examples 1 Strings (behave like tuples):
cool_show=“The Monty Python Show”
print len(cool_show) 21
cool_name1=cool_show[4:9]
cool_name2=cool_show[-11:-5]
print cool_name2+ “ and ”+cool_name1+ “ are cool!”
Python and Monty are cool! T h e M o n t y P S w 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
-21
-20
-19
-18
-17
-16
-15
-14
-13
-12
-11
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
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52. Sequences: Examples 2 PE6850 PE6800 PE2800 PE2850 PE1855MC PE1850
More fun with Lists:
PowerEdge8G = [“PE6850”, “PE6800”, “PE2800”, “PE2850”, “PE1855MC”, “PE1850”]
print max(PowerEdge8G)
PE6850
print min(PowerEdge8G)
PE1850
print “PE2850” in PowerEdge8G 1
print “PE1800” not in PowerEdge8G
PE6850
PE6800
PE2800
PE2850
PE1855MC
PE1850 1 2 3 4 5 -6 -5 -4 -3 -2 -1
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53. Dictionary Overview Python has one mapping type: Dictionary
A Dictionary contains key, value pairs
mydict[key] = value
The values can be any python object
The keys must be python objects that can be compared by value, often strings, ints, tuples.
Dicts are created using curly brackets: { }
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54. Dictionary: Operations
a and b are dicts, k is a key, v is a value:
len(a) # number of items in dict a
a[k] # get value for key k in a
del a[k] # delete key, value a[k] from a
a.clear() # delete all items in a
a.copy() # shallow copy of a
a.has_key(k) # 1 if k in a else, 0
a.items() # list of (key,value) pairs in a
a.keys() # list of keys in a
a.update(b) # for k in b.keys(): a[k] = b[k]
a.values() # list of values in a
a.get(k,x) # get value for k in a, otherwise x if None
a.popitem() # remove and return an arbitrary k,v pair
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55. Dictionary: Examples
toyota_91 = {‘sport’: “supra”, ‘midsize’: “camry”, ‘compact’: “corolla”, ‘subcompact’: “tercel”, ‘fullsize’: “cressida”}
print toyota_91
{‘sport’: ‘supra’, ‘midsize’: ‘camry’, ‘compact’: ‘corolla’, ‘subcompact’: ‘tercel’, ‘fullsize’: ‘cressida’ }
toyota_07 = toyota_91.copy()
print toyota_07
toyota_07[‘fullsize’] = ‘avalon’
del toyota_07[‘sport’]
toyota_07[‘sporty’] = ‘matrix’
toyota_07[‘pickup’] = ‘tacoma’
toyota_07[‘subcompact’] = ‘yaris’
{‘midsize’: ‘camry’, ‘compact’: ‘corolla’, ‘subcompact’: ‘yaris’, ‘fullsize’: ‘avalon’, ‘sporty”: ‘matrix’, ‘pickup’: ‘tacoma’}
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56. Deep Copying Mutable types change in place.
Must deep copy else shared reference.
List:
newl = l[:] # using slice, or
newl = list(l) # using list casting fn
Dictionary:
newd = {}
for k, v in d.items(): # traversal
newd[k] = v
Or copy module:
import copy
x = copy.copy(y) # make a shallow copy of y
x = copy.deepcopy(y) # make a deep copy of y
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57. Module 5 Lab
DATA STRUCTURES
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58. Module 5 Lab 1. Print following using a single print statement:
Copyright (C) 2007, Dell, Inc.
All Rights Reserved
2. For the following string:
string1 = “A quick brown fox jumps over the lazy dog.”
a. what can ? be if string1[?] is dog.
b. how about if string1[?] is jumps over the lazy dog.
c. and what if it string1[?] is A
3. Does the code below work?
mylist = [1,2,3]
mylist.append(a)
4. How about this code:
mylist = (1,2,3)
mylist.append(4)
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59. Module 6
Python files
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60. Overview So far the code we have written was in the interpreter.
If we exit the interpreter all the code is lost!
So we need to use a text editor and write the code to a file.
The file is referred to as a Python:
file
module
script
program
etc
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61. Syntax Typical Python module: #!/usr/bin/env python2 #
# – mfk – created
def fn1(params):
code…
def fn2(params):
Typical Python script:
#!/usr/bin/env python2 #
# – mfk – created
def fn1(params):
code…
def fn2(params):
if __name__ == “__main__”:
code…
fn1(args)
fn2(args)
code…
fn1(args)
fn2(args)
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62. Notes Tabs signify blocks.
Potential for Tab / Space confusion.
Configure text editor to convert tabs to spaces.
Eclipse, notepad, etc are ok.
Vi needs configuration.
No semicolon required to close end line of code.
Can use semicolon to specify multiple instructions on same line.
Multi-line separator is \.
Comments are precede with a #
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63. Module 6 Lab
Python FILES
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64. Module 6 Lab Are the following code blocks valid: block1.py: 2+2; 1+14 2
block2.py:
1+ \ 1
block3.py:
2+2
1+1
File "<stdin>", line 2
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65. Module 7
Conditionals
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66. Overview Value testing Comparisons if statement if-else if-elif-else
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67. Value Testing The following are considered false:
None # python’s null type
False
Zero of any numeric type, 0, 0.0, 0L
An empty sequence [ ], ( ), ‘’, “”
An empty mapping { }
What is considered true?
All other values including True
*built-in constants
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68. True / False / None False + 99 99 True + 99 100 None + 1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'
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69. Comparisons Syntax for comparisons: Boolean:
>,>= # greater than, greater than or equal to
<,<= # less than, less than or equal to
== # equal
!=, <> # not equal to
is # is object identity
is not # negated object identity
Boolean:
x or y # if x is false, then y, else x
x and y # if x is false, then x, else y
not x # if x is false, then 1, else 0
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70. Comparisons Example 1==1 1==0 “a”>“b” 1 is 1 # confusing
“a”>“b”
1 is 1 # confusing
word=“Hello”
word2=word
word is word2
> print id(word), id(word2) # why did it work?
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71. if statement Syntax for if statement: Examples: n=m=1 o=2 if n==o:
code…
if comparison:
code… # execute this regardless of if result
Examples:
n=m=1
o=2
if n==o:
… print “n and o match!”
*nothing!*
if n==m:
… print “n and m match!”
n and m match!
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72. if-else statement Syntax for if-else: Examples: n=m=1 o=2 if n==o:
code…
if comparison:
else:
Examples:
n=m=1
o=2
if n==o:
… print “n and o match!”
… else:
… print “n and m match!”
n and m match! # not entirely true!
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73. if-elif-else statement
Syntax for if-elif-else:
code…
if comparison:
elif comparison: # multiple elifs allowed (switch-case)
else:
Examples:
n=m=1
o=2
if n==o:
… print “n and o match!”
… elif n==m:
… print “n and m match!”
… else:
print “sorry no matches!”
n and m match!
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74. Module 8
Loops
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75. Overview While statement For statement range() function
break, continue & pass statements
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76. while statement Syntax for while: ch=97 while ch <= 122:
code…
while condition: # while condition is true
else: # execute only if condition becomes false
code… # execute this after while loop
ch=97
while ch <= 122:
… print chr(ch), # , means stay on same line
… ch = ch + 1 # infinite loop w/o this line
a b c d e f g h I j k l m n o p q r s t u v w x y z
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77. for statement
for statement in Python != C, Pascal, Java etc, more = bash
Syntax for for:
code…
for an_item in items: # while condition is true
code… # loop till all items used
else: # execute if all items used
code… # execute after for loop
list = [“a”, “b”, “c”]
for item in list:
… print item,
a b c
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78. Traversals Traversing a sequence using for:
poweredge8g = [“PE6850”, “PE6800”, “PE2850”, “PE1850”, “PE1800”]
for a_server in poweredge8g:
… print a_server,
PE6850 PE6800 PE2850 PE1850 PE1800
Traversing a mapping using for:
> toyota_07={‘midsize’: ‘camry’, ‘compact’: ‘corolla’, ‘subcompact’: ‘yaris’, ‘fullsize’: ‘avalon’, ‘sporty”: ‘matrix’, ‘pickup’: ‘tacoma’}
for k, v in toyota_07.items():
… print k+“=”+v,
midsize=camry compact=corolla subcompact=echo fullsize=avalon sporty=matrix pickup=tacoma
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79. Traversals w/ enumerate
Traversing a sequence using for and show indices:
poweredge8g = [“PE6850”, “PE6800”, “PE2850”, “PE1850”, “PE1800”]
index = 0
for a_server in poweredge8g:
… print str(index)+”:”, a_server,
… index += 1
0: PE6850 1: PE6800 2: PE2850 3: PE1850 4: PE1800
w/ enumerate:
for index, a_server in enumerate(poweredge8g):
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80. range() range() generates arithmetic progressions using lists:
Syntax for range:
range([start],stop,[step])
if no start, 0 assumed, if no step, 1 assumed
range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
range(5, 10)
[5, 6, 7, 8, 9]
range(0, 10, 2)
[0,2,4,6,8]
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81. break, continue & pass
The break statement will break out of the smallest enclosing for/while loop.
The continue statement will go to next iteration of loop without running remaining code in current iteration.
The pass statement is essentially a no-op.
Loop statements can have an else clause; runs when:
loop terminates through exhaustion of the list (with for) or
condition becomes false (with while),
but not when the loop is terminated by a break statement.
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82. for-else example for n in range(2, 10): # loop to search for primes
… for x in range(2, n):
… if n % x == 0:
… print n, ‘equals’, x, ‘*’, n/x
… break
… else:
… print n, ‘is a prime number’
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3
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83. Module 8 Lab
Loops
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84. Module 8 Lab
1. Select a number between 1 and Put this number in your program. Allow the user to guess the number from a prompt. The user should be prompted to guess the number until either they guess the correct number, or they hit “x” to exit the program.
Extra Credit:
Each time the user guesses, tell user whether they need to guess higher or lower
When the user wins, tell them how many times they tried to guess the right number.
2. Write the Prime Number detection loop w/o the for-else syntax.
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85. Module 8 Lab 2
Make a dictionary program. Supporting following functions:
Lookup a word (getting its definition).
Add a word and its definition.
Redefine a word’s definition.
Delete a word (and its definition).
List all words in dictionary.
Provide a mechanism to quit from this program.
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86. Module 9
functions
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87. Overview
Function syntax: def functionName([arg1, arg2…]): [“doc string”] # optional doc string describing fn code… # code block [return data] # function can optionally return data # return can return multiple items a, b, c = functionName() # function call
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88. Examples y=4 def func(y): … print y, … y = 3 … print y func(y) print y
4 3
print y 4
list=range(5)
def func2(alist):
... print alist
… alist.append(100)
func2(list)
[0, 1, 2, 3, 4]
print list
[0, 1, 2, 3, 4, 100]
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89. Parameter Formats Default values:
def car(make, model, doors=4, wheels=4):
car(“Ford”, “Mustang”, 2)
car(“Toyota”, “Corolla”)
car(“Mr.”, “Bean’s”, 3, 3)
What if I had a Ford F550 Supercrew Dually: 4 doors, 6 wheels, I don’t want to pass 4 for the doors, only the 6 for the wheels.
Keyword values:
car(“Ford”,“F550 Supercrew”, wheels=6)
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90. *,** parameters
a * preceding an argument indicates an argument sequence or arbitrary length:
def arbitrary(*a):
return a
print arbitrary(“a”,“b”,3)
(a, b, 3)
a ** preceding an argument indicates it will be a dictionary containing key/value pairs of all passed keyword args.
def coolFunc(**optDict):
return optDict
> print coolFunc(abc=“def”, ghi=“jkl”)
{‘abc’: ‘def’, ‘ghi’: ‘jkl’}
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91. Function helpers List/Sequence operations: Examples: five=[1,2,3,4,5]
filter(function, list), map(function, list), reduce(function, list)
Examples:
five=[1,2,3,4,5]
def multiply(x,y):
… return x*y
reduce(multiply, five) #(((((1)*2)*3)*4)*5) ie 5!
120
def threeandup(x):
… if x >= 3:
… return 1
… else:
… return 0
filter(threeandup, five)
[3,4,5]
def squares(x):
… return x*x
map(squares, five)
[1, 4, 9, 16, 25]
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92. Module 9 Lab
Functions
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93. Module 9 Lab
A palindrome is a word that is spelled the same way forwards as it is backwards. Some examples include “radar”, “dad”, “malayalam” and “a man a plan a canal panama”. Write a function testPalindrome() that returns a True if the string is a palindrome and a False otherwise.
Extra Credit:
Use recursion.
Modify dictionary program to use functions.
Write a Jumble word program that randomly selects a string, jumbles it, and asks user to guess the word, interaction w/ user ~ guess a number game…
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94. Module 1:
Exceptions
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95. Exceptions Overview When an error occurs
An exception is raised (=thrown in Java).
The interpreter jumps out of code blocks till the exception is caught by a try block, or
If the exception is not caught, interpreter quits code execution with the exception.
All errors in Python are exceptions (hence no seg faults).
For eg: 1/0, 3+“3”, (3, 4).append(“abc”)
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96. try…except syntax
try: # program logic goes here.. except Exception1: # code to handle exception, Exception1 except Exception2, Exception3: # code to handle exceptions, 2 or 3.. except: # code to catch all other exception types. else: # run this if there were NO exceptions!
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97. try…except…finally
try: # program logic goes here.. except Exception1: # code to handle exception, Exception1 except Exception2, Exception3: # code to handle exceptions, 2 or 3.. except: # code to catch all other exception types. else: # run this if there were NO exceptions! finally: # run this code REGARDLESS of exception or not
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98. example
try: cc=open('carddata.txt',"r") lines=cc.readlines() except IOError: print "error reading file!" except: print "some other error“ finally: print “closing file…” cc.close()
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[exception.py]

99. Trapping Ctr-C import sys import time try: while True:
print "processing stuff..."
time.sleep(1)
except KeyboardInterrupt:
print "Ctrl-C pressed... exiting..."
sys.exit(1)
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[exception_trap.py]

100. Module 10
Modules
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101. Using modules You can load modules using the import statement:
import os
from ConfigParser import ConfigParser
from os import * # bad, pollutes namespace!
mymodule.py:
def hello():
print “hello world!”
def hello2():
print “hello monty python!”
import mymodule # importing mymodule.py
dir(mymodule)
[‘__builtins__’, ‘__doc__’, ‘__file__’, ‘__name__’, ‘hello’, ‘hello2’]
mymodule.hello2()
hello monty python!
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102. Dynamic execution You can also load modules dynamically: test.py:
print “abcdefg”
if timeToImport==True:
execfile(“c:\test.py”, globals(), locals())
abcdefg
You can also run code dynamically:
def bob():
print “My name is bob”
name=raw_input() #dynamic function pointer
bob
exec(name+ “()”)
My name is bob
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103. Module search path
The Python module search path can be set dynamically:
import sys
sys.path.append(“c:\temp\my_python”)
print sys.path
[…, “c:\temp\my_python”]
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104. Questions
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