PythonPython Csc 667/867 Course note credit to PrenticeHall.

PythonPythonPythonPython

Csc 667/867Csc 667/867

Course note credit to PrenticeHall

2

Printing a Line of Text

• Python Online Tutorialhttp://www.python.org/doc/current/tut/

• Python Reference Manualhttp://docs.python.org/ref/contents.html

• Executing– Saving as a file

• Type code into a .py file and save it• To run it type python fileName.py

– Executing code

• Type python in the command line• Runs the python interpreter

3

Adding Integers

• Functions– The raw_input function

• Used to retrieve data from the user

– The int function• Used to convert strings to integers

4

1 1 # Fig. 2.7: fig02_07.py# Fig. 2.7: fig02_07.py

2 2 # Simple addition program.# Simple addition program.

3 3

4 4 # prompt user for input# prompt user for input

55 integer1 = raw_input( integer1 = raw_input( "Enter first integer:\n""Enter first integer:\n" ) ) # read string# read string

6 6 integer1 = int( integer1 ) integer1 = int( integer1 ) # convert string to integer# convert string to integer

7 7

8 8 integer2 = raw_input( integer2 = raw_input( "Enter second integer:\n""Enter second integer:\n" ) ) # read string# read string

99 integer2 = int( integer2 ) integer2 = int( integer2 ) # convert string to integer# convert string to integer

10 10

1111 sum = integer1 + integer2 sum = integer1 + integer2 # compute and assign sum# compute and assign sum

12 12

13 13 printprint "Sum is""Sum is", sum , sum # print sum# print sum

Enter first integer:

45

Enter second integer:

72

Sum is 117

5

Another Program: Adding Integers

Python 2.2b2 (#26, Nov 16 2001, 11:44:11) [MSC 32 bit (Intel)] on win32

Type "help", "copyright", "credits" or "license" for more information.

>>> value1 = raw_input( "Enter an integer: " )

Enter an integer: 2

>>> value2 = raw_input( "Enter an integer: " )

Enter an integer: 4

>>> print value1 + value2

24

Fig. 2.8 Adding values from raw_input (incorrectly) without converting to integers (the result should be 6).

6

Arithmetic• Symbols

– * = multiply– / = divide– % = modulus– ** = exponential– // = floor division

• Only available in Python 2.2• Must use from __future__ import division

• Order– Operators are done in order of parenthesis,

exponents, multiple and divide (left to right), and lastly add and subtract (left to right)

7

Arithmetic

Operator(s) Operation(s) Order of Evaluation (Precedence)

( ) Parentheses Evaluated first. If the parentheses are nested, the expression in the innermost pair is evaluated first. If there are several pairs of parentheses “on the same level” (i.e., not nested), they are evaluated left to right.

** Exponentiation Evaluated second. If there are several, they are evaluated right to left.

* / // % Multiplication Division Modulus

Evaluated third. If there are several, they are

evaluated left to right. [Note: The // operator is new in version 2.2]

+ - Addition Subtraction

Evaluated last. If there are several, they are evaluated left to right.

Fig. 2.16 Precedence of arithmetic operators.

8

Augmented Assignment Symbols

Assignment symbol

Sample expression

Explanation Assigns

Assume: c = 3, d = 5, e = 4, f = 2, g = 6, h = 12

+= c += 7 c = c + 7 10 to c

-= d -= 4 d = d - 4 1 to d

*= e *= 5 e = e * 5 20 to e

**= f **= 3 f = f ** 3 8 to f /= g /= 3 g = g / 3 2 to g

%= h %= 9 h = h % 9 3 to h

Fig. 3.16 Augmented arithmetic assignment symbols.

9

Logical Operators• Operators

– and• Evaluates to true if both expressions are true

– or• Evaluates to true if at least one expression is true

– not• Returns true if the expression is false• Not required in any program

10

String Formatting• Strings

– Unlike other languages strings are a built in data type

• Allows for easy string manipulation

– Double quote strings• Single quotes need not be escaped

– Single quote strings• Double quotes need not be escaped

– Triple quoted strings• Do not need any escape sequence• Used for large blocks of text

11

1 1 # Fig. 2.18: fig02_18.py# Fig. 2.18: fig02_18.py2 2 # Creating strings and using quote characters in strings.# Creating strings and using quote characters in strings.3 3 4 4 printprint "This is a string with \"double quotes.\"" "This is a string with \"double quotes.\""55 printprint 'This is another string with "double quotes."' 'This is another string with "double quotes."'6 6 printprint 'This is a string with \'single quotes.\'' 'This is a string with \'single quotes.\''77 printprint "This is another string with 'single quotes.'" "This is another string with 'single quotes.'"88 printprint """This string has "double quotes" and 'single quotes'. """This string has "double quotes" and 'single quotes'.9 9 You can even do multiple lines.""" You can even do multiple lines."""10 10 printprint '''This string also has "double" and 'single' quotes.''' '''This string also has "double" and 'single' quotes.'''

This is a string with "double quotes."

This is another string with "double quotes."

This is a string with 'single quotes.'

This is another string with 'single quotes.'

This string has "double quotes" and 'single quotes'.

You can even do multiple lines.

This string also has "double" and 'single' quotes.

12

2 2 # String formatting.# String formatting.3 3 4 4 integerValue =integerValue = 4237 42375 5 printprint "Integer ""Integer ", integerValue, integerValue6 6 printprint "Decimal integer %d""Decimal integer %d" % integerValue % integerValue7 7 printprint "Hexadecimal integer %x\n""Hexadecimal integer %x\n" % integerValue % integerValue8 8 9 9 floatValue =floatValue = 123456.789 123456.78910 10 printprint "Float""Float", floatValue, floatValue11 11 printprint "Default float %f""Default float %f" % floatValue % floatValue1212 printprint "Default exponential %e\n""Default exponential %e\n" % floatValue % floatValue13 13 14 14 printprint "Right justify integer (%8d)""Right justify integer (%8d)" % integerValue % integerValue1515 printprint "Left justify integer (%-8d)\n""Left justify integer (%-8d)\n" % integerValue % integerValue16 16 17 17 stringValue = stringValue = "String formatting""String formatting"18 18 printprint "Force eight digits in integer %.8d""Force eight digits in integer %.8d" % integerValue % integerValue19 19 printprint "Five digits after decimal in float %.5f""Five digits after decimal in float %.5f" % floatValue % floatValue20 20 printprint "Fifteen and five characters allowed in string:""Fifteen and five characters allowed in string:"2121 printprint "(%.15s) (%.5s)""(%.15s) (%.5s)" % ( stringValue, stringValue ) % ( stringValue, stringValue )

13

Integer 4237

Decimal integer 4237

Hexadecimal integer 108d

Float 123456.789

Default float 123456.789000

Default exponential 1.234568e+005

Right justify integer ( 4237)

Left justify \integer (4237 )

Force eight digits in integer 00004237

Five digits after decimal in float 123456.78900

Fifteen and five characters allowed in string:

(String formatti) (Strin)

14

Indentation• Indenting

– Used to delimit code– Python uses no end of statement character– Therefore a new line of code is determined by return

space– Indenting is the same way

• Python does not use {} to enclose a multi-line statement

• The indentation must be exactly the same same

– There is no exact rule for the number of spaces but they are generally in groups of three

15

Lines• Logical Lines (

http://docs.python.org/ref/logical.html)• Physical Lines • Explicit Line Joining

• Implicit Line Joining

if 1900 < year < 2100 and 1 <= month <= 12 \ and 1 <= day <= 31 and 0 <= hour < 24 \ and 0 <= minute < 60 and 0 <= second < 60: # Looks like a valid date

return 1

month_names = ['Januari', 'Februari', 'Maart', # These are the 'April', 'Mei', 'Juni', # Dutch names 'Juli', 'Augustus', 'September', # for the months 'Oktober', 'November', 'December'] # of the year

16

Control Structure• Sequential order

– Statements are executed in the order they are written• Transfer of control

– A program executes a statement other than the following one

– The goto statement• Allows a program to go to a wide range of areas in the code• Structured programming was broken with the use of goto• Any code can be written without a goto statement

– Selection structure• The if statement• The if/else statement• The if/elif/else statement

– Repetition structure• The while repetition structure• The for repetition structure

17

11 # Control Statement examples# Control Statement examples22 # Class average program with counter-controlled # Class average program with counter-controlled repetition.repetition.3344 # initialization phase# initialization phase55 total =total = 0 0 # sum of grades# sum of grades66 gradeCounter =gradeCounter = 1 1 # number of grades entered# number of grades entered7788 # processing phase# processing phase99 whilewhile gradeCounter <= gradeCounter <= 10 10: : # loop 10 times# loop 10 times1010 grade = raw_input( grade = raw_input( "Enter grade: ""Enter grade: " ) ) # get one grade# get one grade1111 grade = int( grade ) grade = int( grade ) # convert string to an integer# convert string to an integer1212 total = total + grade total = total + grade1313 gradeCounter = gradeCounter + gradeCounter = gradeCounter + 1 114141515 # termination phase# termination phase1616 average = total /average = total / 10 10 # integer division# integer division1717 printprint "Class average is""Class average is", average, average

18

11 # More control statement example# More control statement example22 # Class average program with sentinel-controlled # Class average program with sentinel-controlled repetition.repetition.3344 # initialization phase# initialization phase55 total =total = 0 0 # sum of grades# sum of grades66 gradeCounter =gradeCounter = 0 0 # number of grades entered# number of grades entered7788 # processing phase# processing phase99 grade = raw_input( grade = raw_input( "Enter grade, -1 to end: ""Enter grade, -1 to end: " ) ) # get one # get one gradegrade1010 grade = int( grade ) grade = int( grade ) # convert string to an integer# convert string to an integer11111212 whilewhile grade != grade != -1-1::1313 total = total + grade total = total + grade1414 gradeCounter = gradeCounter + gradeCounter = gradeCounter + 1 11515 grade = raw_input( grade = raw_input( "Enter grade, -1 to end: ""Enter grade, -1 to end: " ) )1616 grade = int( grade ) grade = int( grade )17171818 # termination phase# termination phase1919 ifif gradeCounter != gradeCounter != 0 0::2020 average = float( total ) / gradeCounter average = float( total ) / gradeCounter2121 printprint "Class average is""Class average is", average, average2222 elseelse::2323 printprint "No grades were entered""No grades were entered"

19

break and continue Statements

• The break statement– Used to make a loop stop looping– The loop is exited and no more loop code is

executed

• The continue statement– Used to continue the looping process– All following actions in the loop are not executed

• But the loop will continue to run

20


2 2 # Using the break statement in a for structure.# Using the break statement in a for structure.

3 3

44 forfor x x inin range( range( 1 1,, 11 11 ): ):

5 5

6 6 ifif x == x == 5 5::

77 breakbreak

8 8

9 9 printprint x, x,

10 10

1111 printprint "\nBroke out of loop at x =""\nBroke out of loop at x =", x, x

1 2 3 4Broke out of loop at x = 5

21

Logical Operators

Python 2.2b2 (#26, Nov 16 2001, 11:44:11) [MSC 32 bit (Intel)] on win32Type "help", "copyright", "credits" or "license" for more information.>>> if 0:... print "0 is true"... else:... print "0 is false"...0 is false>>> if 1:... print "non-zero is true"...non-zero is true>>> if -1:... print "non-zero is true"...non-zero is true>>> print 2 < 31>>> print 0 and 10>>> print 1 and 33

Fig. 3.28 Truth values.

22

Variable Scopedef demo (f_in):

global somevar # shared with main codedemo.tom = 16 # An attribute accessible from main codesomevar += 1f_in = 2demo.another = 12 # A local variable, independent of main codeanother = 13res = f_in+14 # Value passed in (f_in)return res

somevar = 27 # accessed in function via globalanother = 17 # not accessed in functionpval = 16 # accessed in function via parameter

print demo(pval) print pvalprint demo.tom # function attributeprint somevarprint anotherprint demo.another

23

Using Lists

Python 2.2b2 (#26, Nov 16 2001, 11:44:11) [MSC 32 bit (Intel)] on win32Type "help", "copyright", "credits" or "license" for more information.>>> aList = [ 1 ]>>> print aList[ 13 ]Traceback (most recent call last): File "<stdin>", line 1, in ?IndexError: list index out of range

Fig. 5.4 Out-of-range error.

24

1 1 # Fig. 5.5: fig05_05.py# Fig. 5.5: fig05_05.py2 2 # Creating a histogram from a list of values.# Creating a histogram from a list of values.3 3 4 4 values = [] values = [] # a list of values# a list of values5 5 6 6 # input 10 values from user# input 10 values from user7 7 printprint "Enter 10 integers:""Enter 10 integers:"8 8 9 9 forfor i i inin range( range( 10 10 ): ):10 10 newValue = int( raw_input( newValue = int( raw_input( "Enter integer %d: ""Enter integer %d: " % ( i + % ( i + 1 1 ) ) ) ) ) )1111 values += [ newValue ] values += [ newValue ]12 12 13 13 # create histogram# create histogram14 14 printprint "\nCreating a histogram from values:""\nCreating a histogram from values:"15 15 printprint "%s %10s %10s""%s %10s %10s" % ( % ( "Element""Element", , "Value""Value", , "Histogram""Histogram" ) )16 16 17 17 forfor i i inin range( range( len( values ) ):len( values ) ):1818 printprint "%7d %10d %s""%7d %10d %s" % ( i, values[ i ], % ( i, values[ i ], "*""*" * values[ i ] ) * values[ i ] )

Fig05_05.pyFig05_05.pyProgram OutputProgram OutputFig05_05.pyFig05_05.py

Program OutputProgram Output

Enter 10 integers:Enter integer 1: 19Enter integer 2: 3Enter integer 3: 15Enter integer 4: 7Enter integer 5: 11Enter integer 6: 9Enter integer 7: 13Enter integer 8: 5Enter integer 9: 17Enter integer 10: 1 Creating a histogram from values:Element Value Histogram 0 19 ******************* 1 3 *** 2 15 *************** 3 7 ******* 4 11 *********** 5 9 ********* 6 13 ************* 7 5 ***** 8 17 ***************** 9 1 *

26


2 2 # Creating and accessing tuples.# Creating and accessing tuples.

3 3

4 4 # retrieve hour, minute and second from user# retrieve hour, minute and second from user

5 5 hour = int( raw_input( hour = int( raw_input( "Enter hour: ""Enter hour: " ) ) ) )

6 6 minute = int( raw_input( minute = int( raw_input( "Enter minute: ""Enter minute: " ) ) ) )

7 7 second = int( raw_input( second = int( raw_input( "Enter second: ""Enter second: " ) ) ) )

8 8

99 currentTime = hour, minute, second currentTime = hour, minute, second # create tuple# create tuple

10 10

1111 printprint "The value of currentTime is:""The value of currentTime is:", currentTime, currentTime

12 12

13 13 # access tuple# access tuple

14 14 printprint "The number of seconds since midnight is", \ "The number of seconds since midnight is", \

1515 ( currentTime[ ( currentTime[ 0 0 ] * ] * 3600 3600 + currentTime[ + currentTime[ 1 1 ] * ] * 60 60 + +

1616 currentTime[ currentTime[ 2 2 ] ) ] )

Enter hour: 9Enter minute: 16Enter second: 1The value of currentTime is: (9, 16, 1)The number of seconds since midnight is 33361

27


2 2 # Creating, accessing and modifying a dictionary.# Creating, accessing and modifying a dictionary.

3 3

4 4 # create and print an empty dictionary# create and print an empty dictionary

55 emptyDictionary = {}emptyDictionary = {}

6 6 printprint "The value of emptyDictionary is:""The value of emptyDictionary is:", emptyDictionary, emptyDictionary

7 7

8 8 # create and print a dictionary with initial values# create and print a dictionary with initial values

99 grades = { grades = { "John""John":: 87 87, , "Steve""Steve":: 76 76, , "Laura""Laura":: 92 92, , "Edwin""Edwin":: 89 89 } }

10 10 printprint "\nAll grades:""\nAll grades:", grades, grades

11 11

12 12 # access and modify an existing dictionary# access and modify an existing dictionary

13 13 printprint "\nSteve's current grade:""\nSteve's current grade:", grades[ , grades[ "Steve""Steve" ] ]

1414 grades[ grades[ "Steve""Steve" ] = ] = 90 90

15 15 printprint "Steve's new grade:""Steve's new grade:", grades[ , grades[ "Steve""Steve" ] ]

16 16

17 17 # add to an existing dictionary# add to an existing dictionary

1818 grades[ grades[ "Michael""Michael" ] = ] = 93 93

19 19 printprint "\nDictionary grades after modification:""\nDictionary grades after modification:"

20 20 printprint grades grades

21 21

22 22 # delete entry from dictionary# delete entry from dictionary

2323 deldel grades[ grades[ "John" "John" ]]

24 24 printprint "\nDictionary grades after deletion:""\nDictionary grades after deletion:"

25 25 printprint grades grades

28

The value of emptyDictionary is: {} All grades: {'Edwin': 89, 'John': 87, 'Steve': 76, 'Laura': 92} Steve's current grade: 76Steve's new grade: 90 Dictionary grades after modification:{'Edwin': 89, 'Michael': 93, 'John': 87, 'Steve': 90, 'Laura': 92} Dictionary grades after deletion:{'Edwin': 89, 'Michael': 93, 'Steve': 90, 'Laura': 92}

29


2 2 # Sorting a list.# Sorting a list.

3 3

4 4 aList = [aList = [ 2 2,, 6 6,, 4 4,, 8 8,, 10 10,, 12 12,, 89 89,, 68 68,, 45 45,, 37 37 ] ]

5 5

6 6 printprint "Data items in original order""Data items in original order"

7 7

8 8 forfor item item inin aList: aList:

99 printprint item, item,

10 10

1111 aList.sort()aList.sort()

12 12

13 13 printprint "\n\nData items after sorting""\n\nData items after sorting"

14 14

15 15 forfor item item inin aList: aList:

1616 printprint item, item,

17 17

18 18 printprint

Data items in original order2 6 4 8 10 12 89 68 45 37 Data items after sorting2 4 6 8 10 12 37 45 68 89

30

List and Dictionary Methods

Python 2.2b2 (#26, Nov 16 2001, 11:44:11) [MSC 32 bit (Intel)] on win32Type "help", "copyright", "credits" or "license" for more information.>>> dictionary = { "listKey" : [ 1, 2, 3 ] }>>> shallowCopy = dictionary.copy() # make a shallow copy>>> dictionary[ "listKey" ].append( 4 )>>> print dictionary{'listKey': [1, 2, 3, 4]}>>> print shallowCopy{'listKey': [1, 2, 3, 4]} >>> from copy import deepcopy>>> deepCopy = deepcopy( dictionary ) # make a deep copy>>> dictionary[ "listKey" ].append( 5 )>>> print dictionary{'listKey': [1, 2, 3, 4, 5]}>>> print shallowCopy{'listKey': [1, 2, 3, 4, 5]}>>> print deepCopy{'listKey': [1, 2, 3, 4]}

Fig. 5.15 Difference between a shallow copy and a deep copy.

31

Modules• Check

http://www.python.org/doc/current/tut/node8.html• Import, from

• The Module Search Path – in the current directory– And then in the list of directories specified by the

environment variable PYTHONPATH # Fibonacci numbers module def fib(n):# write Fibonacci series up to n a, b = 0, 1 while b < n: print b, a, b = b, a+b def fib2(n): # return Fibonacci series up to n result = [] a, b = 0, 1 while b < n: result.append(b) a, b = b, a+b return result

Fibo.py

>>> import fibo >>> fibo.fib(1000) 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 >>> fibo.fib2(100) [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]>>> fibo.__name__ 'fibo' If you intend to use a function often you can assign it to a local name: >>> fib = fibo.fib >>> fib(500) 1 1 2 3 5 8 13 21 34 55 89 144 233 377

>>> from fibo import fib, fib2 >>> fib(500)

32

CGI modulehttp://docs.python.org/lib/module-cgi.html

form = cgi.FieldStorage() if not (form.has_key("name") and form.has_key("addr")):

print "<H1>Error</H1>" print "Please fill in the name and addr fields." return

print "<p>name:", form["name"].value print "<p>addr:", form["addr"].value …value = form.getlist("username") usernames = ",".join(value) …fileitem = form["userfile"]

33

1 1 #!c:\Python\python.exe#!c:\Python\python.exe


3 3 # Program displaying CGI environment variables.# Program displaying CGI environment variables.

4 4 importimport os os

66 importimport cgi cgi

7 7

8 8 defdef printHeader( title ): printHeader( title ):

9 9 printprint """Content-type: text/html """Content-type: text/html <?xml version = "1.0" encoding = "UTF-8"?> <?xml version = "1.0" encoding = "UTF-8"?>

12 12 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"

14 14 "DTD/xhtml1-strict.dtd"> "DTD/xhtml1-strict.dtd">

15 15 <html xmlns = "http://www.w3.org/1999/xhtml"><html xmlns = "http://www.w3.org/1999/xhtml">

16 16 <head><title>%s</title></head><body>"""<head><title>%s</title></head><body>""" % title % title

19 19 rowNumber =rowNumber = 0 0

21 21 backgroundColor = backgroundColor = "white""white"

23 23 printHeader( printHeader( "Environment Variables""Environment Variables" ) )

2424 printprint """<table style = "border: 0">""""""<table style = "border: 0">"""

25 25

26 26 # print table of cgi variables and values# print table of cgi variables and values

2727 forfor item item inin os.environ.keys(): os.environ.keys():

28 28 rowNumber += rowNumber += 1 1

30 30 ifif rowNumber % rowNumber % 2 2 == == 0 0: : # even row numbers are white# even row numbers are white

31 31 backgroundColor = backgroundColor = "white""white"

32 32 elseelse: : # odd row numbers are grey# odd row numbers are grey

33 33 backgroundColor = backgroundColor = "lightgrey""lightgrey"• printprint """<tr style = "background-color: %s">"""<tr style = "background-color: %s"> <td>%s</td><td>%s</td> <td>%s</td><td>%s</td>

• </tr>"""</tr>""" % ( backgroundColor,cgi.escape( item ), cgi.escape(os.environ[ item ])) % ( backgroundColor,cgi.escape( item ), cgi.escape(os.environ[ item ])) 3939 printprint """</table></body></html>""""""</table></body></html>"""

Function cgi.escape takes

a string and returns a properly

formatted XHMTL string

34

fig06_05.pyfig06_05.py

35


2 2 importimport os os

6 6 importimport cgi cgi

7 7


9 9 printprint """Content-type: text/html"""Content-type: text/html

10 10

11 11 <?xml version = "1.0" encoding = "UTF-8"?> <!DOCTYPE html PUBLIC<?xml version = "1.0" encoding = "UTF-8"?> <!DOCTYPE html PUBLIC

13 13 "-//W3C//DTD XHTML 1.0 Strict//EN“ "DTD/xhtml1-strict.dtd"> "-//W3C//DTD XHTML 1.0 Strict//EN“ "DTD/xhtml1-strict.dtd">

15 15 <html xmlns = "http://www.w3.org/1999/xhtml"> <html xmlns = "http://www.w3.org/1999/xhtml"> <head><title>%s</title></head><head><title>%s</title></head>

17 17 <body>"""<body>""" % title % title

19 19

20 20 printHeader( printHeader( "QUERY_STRING example""QUERY_STRING example" ) )

21 21 printprint "<h1>Name/Value Pairs</h1>""<h1>Name/Value Pairs</h1>"

22 22

2323 query = os.environ[ query = os.environ[ "QUERY_STRING""QUERY_STRING" ] ]

24 24

25 25 ifif len( query ) == len( query ) == 0 0::

26 26 printprint """<p><br />"""<p><br />

27 27 Please add some name-value pairs to the URL above. Please add some name-value pairs to the URL above.

28 28 Or try <a href = "fig06_06.py?name=Veronica&age=23">this</a>. Or try <a href = "fig06_06.py?name=Veronica&age=23">this</a>.

30 30 </p>"""</p>"""

31 31 elseelse: :

32 32 printprint """<p style = "font-style: italic">"""<p style = "font-style: italic">

33 33 The query string is '%s'.</p>"""The query string is '%s'.</p>""" % cgi.escape( query ) % cgi.escape( query )

3434 pairs = cgi.parse_qs( query ) pairs = cgi.parse_qs( query )

35 35 forfor key, value key, value inin pairs.items(): pairs.items():

37 37 printprint "<p>You set '%s' to value %s</p>"""<p>You set '%s' to value %s</p>"" % \ % \

38 38 ( key, value ) ( key, value )

40 40 printprint "</body></html>""</body></html>"

37


2 2 importimport cgi cgi

6 6


8 8 printprint """Content-type: text/html"""Content-type: text/html

9 9

10 10 <?xml version = "1.0" encoding = "UTF-8"?> <!DOCTYPE html PUBLIC<?xml version = "1.0" encoding = "UTF-8"?> <!DOCTYPE html PUBLIC

12 12 "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd"> "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd">

14 14 <html xmlns = "http://www.w3.org/1999/xhtml"><html xmlns = "http://www.w3.org/1999/xhtml">

15 15 <head><title>%s</title></head><head><title>%s</title></head>

16 16

17 17 <body>"""<body>""" % title % title

18 18

19 19 printHeader( printHeader( "Using 'post' with forms""Using 'post' with forms" ) )

20 20 printprint """<p>Enter one of your favorite words here:<br /></p>"""<p>Enter one of your favorite words here:<br /></p>

2121 <form method = "post" action = "fig06_09.py"> <form method = "post" action = "fig06_09.py">

22 22 <p><p>

23 23 <input type = "text" name = "word" /> <input type = "text" name = "word" />

24 24 <input type = "submit" value = "Submit word" /> <input type = "submit" value = "Submit word" />

25 25 </p></p>

26 26 </form>""" </form>"""

27 27

28 28 pairs = cgi.parse()pairs = cgi.parse()

29 29

30 30 ifif pairs.has_key( pairs.has_key( "word""word" ): ):

31 31 printprint """<p>Your word is:"""<p>Your word is:

32 32 <span style = "font-weight: bold">%s</span></p>"""<span style = "font-weight: bold">%s</span></p>""" \ \

33 33 % cgi.escape( pairs[ % cgi.escape( pairs[ "word""word" ][ ][ 00 ] ) ] )

34 34

35 35 printprint "</body></html>""</body></html>"

39

Cookie

• http://wp.netscape.com/newsref/std/cookie_spec.html– Set-Cookie: NAME=VALUE; expires=DATE;

path=PATH; domain=DOMAIN_NAME; secure – Cookie: NAME1=OPAQUE_STRING1;

NAME2=OPAQUE_STRING2 ...

• Response goes with “Set-Cookie” and then Request comes with “Cookie”

• Cookie example at unicorn.sfsu.edu/cgi-667/cookiecounter.py

40

#!/usr/bin/env python

from Cookie import SimpleCookieimport cgiimport os

def getCookie(initialvalues = {}): """Return a SimpleCookie. If some of the cookie values haven't been set, we'll plunk them into the cookie with the initialValues dict.""" if os.environ.has_key('HTTP_COOKIE'): C = SimpleCookie(os.environ['HTTP_COOKIE']) else: C = SimpleCookie() for key in initialvalues.keys(): if not C.has_key(key): C[key] = initialvalues[key] return C

if __name__ == '__main__': cookie = getCookie({'counter': 0}) cookie['counter'] = int(cookie['counter'].value) + 1

print cookie print "content-type: text/plain\n\n"

print "Here's our count:", cookie['counter'].value

Check http://docs.python.org/lib/module-Cookie.html for detail information for cgi module

41

Sequences• Sequence

– Series of items that are often related– Strings are sequences in Python– A sequence is returned by the range function– Elements

• The individual items in each sequence– Referred to by subscripts

• The first is always zero• Obtain one by using sequenceName[ subscript ]• Can also be referred to negatively

– -1 would be the last element of the sequence

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Sequences

Fig. 5.1 Sequence with elements and indices.

-45

6

0

72

1543

-89

0

62

-3

1

6453

-78c[ 11 ]

c[ 10 ]

c[ 9 ]

c[ 8]

c[ 7 ]

c[ 4 ]

c[ 3 ]

c[ 2 ]

c[ 1 ]

c[ 0 ]

c[ 6 ]

c[ 5 ]

Position number of the element within sequence c

Name sequence (c)

c[ -1 ]

c[ -11 ]

c[ -10 ]

c[ -9 ]

c[ -8]

c[- 7 ]

c[ -4 ]

c[- 3 ]

c[ -2 ]

c[ -6 ]

c[ -5 ]

c[ -12 ]

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Creating Sequences• Creations

– Strings• Use quotes• string1 = ""

– Lists• Use brackets• Separate multiple items with a comma• list1 = []

– Tuples• Use parenthesis• Separate multiple items with a comma• tuple = ()

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Using Lists and Tuples• Differences

– Tuples and lists can both contain the same data– For practical purposes though each is used to hold

different types of items

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Using Lists• Lists

– Not restricted to values of the same type• Programmers use lists to hold data that is of the same

type

– The length is not usually predetermined and can vary throughout the program

– Accessing elements out of range• Python exits and an out of range error is displayed

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Using Tuples• Tuples

– Used to contain data that is related but not necessarily of the same type

• Each data item represents a unique piece of the overall portion

– In this case tuples are usually not iterated though– The needed data is accessed before hand

• A person’s name, age and birth date• Again this is not required but is a general rule

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Sequence Unpacking• Unpacking

– A useful shortcut for to assign values to multiple variables in one statement

Sequence Slicing• Slicing

– Allows a programmer to access a portion of a string or element at once

– theSequence [ start:end ]– Returns the portion of the sequence from the

starting position up to the ending position

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2 2 # Unpacking sequences.# Unpacking sequences.

3 3 # create sequences# create sequences

55 aString = aString = "abc""abc"

6 6 aList = [aList = [ 1 1,, 2 2,, 3 3 ] ]

7 7 aTuple = aTuple = "a""a", , "A""A",, 1 1

9 9 # unpack sequences to variables# unpack sequences to variables

10 10 printprint "Unpacking string...""Unpacking string..."

1111 first, second, third = aStringfirst, second, third = aString

12 12 printprint "String values:""String values:", first, second, third, first, second, third

14 14 printprint "\nUnpacking list...""\nUnpacking list..."

1515 first, second, third = aListfirst, second, third = aList

16 16 printprint "List values:""List values:", first, second, third, first, second, third

17 17

18 18 printprint "\nUnpacking tuple...""\nUnpacking tuple..."

1919 first, second, third = aTuplefirst, second, third = aTuple

20 20 printprint "Tuple values:""Tuple values:", first, second, third, first, second, third

21 21

22 22 # swapping two values# swapping two values

23 23 x =x = 3 3

24 24 y =y = 4 4

25 25

26 26 printprint "\nBefore swapping: x = %d, y = %d""\nBefore swapping: x = %d, y = %d" % ( x, y ) % ( x, y )

2727 x, y = y, x x, y = y, x # swap variables# swap variables

28 28 printprint "After swapping: x = %d, y = %d""After swapping: x = %d, y = %d" % ( x, y ) % ( x, y )

Unpacking string...String values: a b c Unpacking list...List values: 1 2 3 Unpacking tuple...Tuple values: a A 1 Before swapping: x = 3, y = 4After swapping: x = 4, y = 3

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2 2 # Slicing sequences.# Slicing sequences.

4 4 # create sequences# create sequences

55 sliceString = sliceString = "abcdefghij""abcdefghij"

6 6 sliceTuple = (sliceTuple = ( 1 1,, 2 2,, 3 3,, 4 4,, 5 5,, 6 6,, 7 7,, 8 8,, 9 9,, 10 10 ) )

7 7 sliceList = [ sliceList = [ "I""I", , "II""II", , "III""III", , "IV""IV", , "V""V", , "VI""VI", , "VII""VII", , "VIII""VIII", , "IX""IX", , "X""X" ] ]

10 10 # print strings# print strings

11 11 printprint "sliceString: ""sliceString: ", sliceString, sliceString

12 12 printprint "sliceTuple: ""sliceTuple: ", sliceTuple, sliceTuple

13 13 printprint "sliceList: ""sliceList: ", sliceList, sliceList

14 14 printprint

16 16 # get slices# get slices

1717 start = int( raw_input( start = int( raw_input( "Enter start: ""Enter start: " ) ) ) )

18 18 end = int( raw_input( end = int( raw_input( "Enter end: ""Enter end: " ) ) ) )

20 20 # print slices# print slices

21 21 printprint "\nsliceString[""\nsliceString[", start, , start, ":"":", end, , end, "] = ""] = ", sliceString[ start:end ], sliceString[ start:end ]

24 24 printprint "sliceTuple[""sliceTuple[", start, , start, ":"":", end, , end, "] = ""] = ", sliceTuple[ start:end ], sliceTuple[ start:end ]

27 27 printprint "sliceList[""sliceList[", start, , start, ":"":", end, , end, "] = ""] = ", sliceList[ start:end ], sliceList[ start:end ]

sliceString: abcdefghijsliceTuple: (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)sliceList: ['I', 'II', 'III', 'IV', 'V', 'VI', 'VII', 'VIII', 'IX', 'X'] Enter start: -4Enter end: -1 sliceString[ -4 : -1 ] = ghisliceTuple[ -4 : -1 ] = (7, 8, 9)sliceList[ -4 : -1 ] = ['VII', 'VIII', 'IX']

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Dictionaries• Dictionaries

– Mapping constructs consisting of key-value pairs• Referred to as hashes in other languages

– Unordered collection of references– Each value is referenced though key in the pair– Curley braces ({}) are used to create a dictionary– When entering values

• Use { key1:value1, … }

– Keys must be immutable values such as strings, numbers and tuples

– Values can be of any Python data type

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List and Dictionary MethodsMethod Purpose

append( item ) Inserts item at the end of the list.

count( element ) Returns the number of occurrences of element in the list.

extend( newList ) Inserts the elements of newList at the end of the list.

index( element ) Returns the index of the first occurrence of element in the list. If element is not in the list, a ValueError exception occurs. [Note: We discuss exceptions in Chapter 12, Exception Handling.]

insert( index, item )

Inserts item at position index.

pop( [index] ) Parameter index is optional. If this method is called without arguments, it removes and returns the last element in the list. If parameter index is specified, this method removes and returns the element at position index.

remove( element ) Removes the first occurrence of element from the list. If element is not in the list, a ValueError exception occurs.

reverse() Reverses the contents of the list in place (rather than creating a reversed copy).

sort( [compare-function] )

Sorts the content of the list in place. The optional parameter

compare-function is a function that specifies the compare

criteria. The compare-function takes any two elements of the list (x and y) and returns -1 if x should appear before y, 0 if the orders of x and y do not matter and 1 if x should appear after

y. [Note: We discuss sorting in Section 5.9.] Fig. 5.12 List methods.

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Method Description

clear() Deletes all items from the dictionary.

copy() Creates and returns a shallow copy of the dictionary (the elements in the new dictionary are references to the elements in the original dictionary).

get( key [, returnValue] ) Returns the value associated with key. If key is not in the

dictionary and if returnValue is specified, returns

the specified value. If returnValue is not specified,

returns None.

has_key( key ) Returns 1 if key is in the dictionary; returns 0 if key is

not in the dictionary.

items() Returns a list of tuples that are key-value pairs.

keys() Returns a list of keys in the dictionary.

popitem() Removes and returns an arbitrary key-value pair as a tuple of two elements. If dictionary is empty, a Key-Error exception occurs. [Note: We discuss

exceptions in Chapter 12, Exception Handling.] This method is useful for accessing an element (i.e., print the key-value pair) before removing it from the dictionary.

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setdefault( key [, dummyValue] )

Behaves similarly to method get. If key is not in the dictionary and dummyValue is specified, inserts the key and the specified value into dictionary. If

dummyValue is not specified, value is None.

update( newDictionary ) Adds all key-value pairs from newDictionary to the current dictionary and overrides the values for keys that already exist.

values() Returns a list of values in the dictionary.

iterkeys() Returns an iterator of dictionary keys. [Note: We discuss iterators in Appendix O, Additional Python 2.2 Features.]

iteritems() Returns an iterator of key-value pairs. [Note: We discuss iterators in Appendix O, Additional Python 2.2 Features.]

itervalues() Returns an iterator of dictionary values. [Note: We discuss iterators in Appendix O, Additional Python 2.2 Features.]

Fig. 5.14 Dictionary methods.

PythonPython Csc 667/867 Course note credit to PrenticeHall.

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