CMPT 165 Unit 8 Advanced Programming - Part 2. Dec. 1 st, 2015

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Gertrude Hawkins
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1 CMPT 165 Unit 8 Advanced Programming - Part 2 Dec. 1 st, 2015

2 Note # # MIME: must be declared in the first line a_markup_str ="""Content-type: text/html <html> <head> <title>my first web script</title> </head> <body> <h1>my first web script</h1> <p>this is a dynamically generated web page.</p> </body> </html> """ print( a_markup_str ) 2

3 Ways to string-formatting 1. Use commas to combine different data types >>> print("hey daddy, does 2 x 2 equal to", 2*2, "?") Hey daddy, does 2 x 2 equal to 4? 2. Use of escape characters: # approach 1 print( "Content-type: text/html") print() # approach 2 print( "Content-type: text/html \n") # newline # other examples: print( "\t<p>hello!</p>") # tab See more here: 3

4 String formatting with %: Example # str= "Content-type: text/html" print( str ) print( ) # declare a multi-line string a_markup_str =""" <html> <head> <title>my first web script</title> </head> <body> <h1>my first web script</h1> <p>this is a dynamically generated web page.</p> </body> </html> """ print( a_markup_str ) 4

5 String formatting with %: Example # str= "Content-type: text/html" print( str ) print( ) # declare a multi-line string a_markup_str =""" <html> <head> <title>%s</title> </head> <body> <h1>%s</h1> <p>this is a dynamically generated web page.</p> </body> </html> """ %(title_str,title_str) # if you have more place holders, use brackets print( a_markup_str ) 5

6 Example of escape characters in use str= "Content-type: text/html" print( str ) print( ) # declare a multi-line string a_markup_str =""" <html> \t<head> \t\t<title>%s</title> \t</head> <body> \t<h1>%s</h1> \t<p>this is a dynamically generated web page.</p> </body> </html> """ %(title_str,title_str) print( a_markup_str ) 6

7 String formatting with % operator Replace parts of string with operand (i.e. following %): %s string %i integer %f floating point number >>> string_variable = "Sue"; >>> z = "My name is %s" %string_variable >>> print(z) My name is Sue >>> yr=91; mon=6; day=22; >>> friend="saurabh"; >>> print("birthdate of %s is %i-%i-%i" %(friend,yr,mon,day)) Birthdate of Saurabh is >>> # Note the order should be preserved >>> total_cost= 1.07*2.00 # cost with tax >>> str = "Total cost comes to $%f" %(total_cost) >>> print( str ) Total cost comes to $

8 FYI: Floating-point number (not integer; has fractional component) = x = x = x 10-3

9 Floating-point: Rounding to m decimal places >>> str = "Total cost comes to $%f" %(total_cost) >>> print( str ) Total cost comes to $ >>> # round to 2 decimal places >>> str = "Total cost comes to $%0.2f" %(total_cost) >>> print( str ) Total cost comes to $2.14 >>> # round to 2 decimal places: skip the 0 >>> str = "Total cost comes to $%.2f" %(total_cost) >>> print( str ) Total cost comes to $2.14 >>> # round to 3 decimal places? >>> str = "Total cost comes to $%.3f" %(total_cost) >>> print( str ) Total cost comes to $2.140 >>> # round to 1 decimal places? >>> str = "Total cost comes to $%.1f" %(total_cost) >>> print( str ) Total cost comes to $2.1

$Putting all together 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 print("content-type: text/html \n") title="example" markup=""" <html> <head> <title>%s</title> </head> <body> <p>let us do some$

10 Putting all together print("content-type: text/html \n") title="example" markup=""" <html> <head> <title>%s</title> </head> <body> <p>let us do some math.</p>""" %title print( markup ) a=100; b=20; their_sum=a+b print("<p>", a, " + ", b, " = ", their_sum, "</p>") print("<p>", a, "+", b, "=", their_sum, "</p>") print('<img src="a_graphics.png" width ="200px"/>') markup2="</body></html>" print( markup2 ) 10

11 1. Use of escape characters: Ways to string-formatting print( "Content-type: text/html") print() print( "Content-type: text/html \n") # newline 2. Defining multi-line string variable (line breaks will be kept): z=""" <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" " """ 3. String-formatting operator % (see SG 9.3 for more details): >>> name1="sue"; z = "My name is %s " % name1 >>> print( z ) My name is Sue >>> name2="ramada"; print "My name is %s %s" % (name1,name2) My name is Sue Ramada 11

12 CMPT 165 User-interaction via Forms & CGI module Dec. 1 st, 2015

Interaction with user via web forms Interaction: User provides input website response (i.e. provide output) Simple client-side (user agent browser) tooltips, a:hover Elaborate: Javascript, Python, etc.

13 Interaction with user via web forms Interaction: User provides input website response (i.e. provide output) Simple client-side (user agent browser) tooltips, a:hover Elaborate: Javascript, Python, etc. Server-side (e.g. web scripts ran on cmpt165.csil.sfu.ca) So far, seen how to generate output dynamically from Python programs i.e. Run web scripts Today: getting user input via web forms 13

14 Example web form 14

15 15

16 Markup for forms Executes some action when user clicks submit button <h1>form Example</h1> <form action="sample.py"> <input type="text" value="default text" /> <input type="text" name="text2" size="6" maxlength="10" /> <input type="submit" value="go!" /> </form> <form action="sample.py"></form> <input type="submit" /> <input type="text" /> Try this out in the HTML/CSS 16

17 Example web form <form> <input> <label> action="" type ="" 17

18 Example web form A label for the first input element Another label element Another label element <form> <input> <label> action="" type ="" 18 An input element of type text with a default value Another input element with no default value A button that executes an action when clicked

19 Markup for forms Regular_webpage.html <h1>form Example</h1> Identifier for element <form action="response_script.py"> <label for= lname">last name (required):</label> <input type="text" name="lname" /> <input type="text" name="fname" /> <input type="submit" value="go!" /> </form> Executes some action when user clicks Q) A block or inline element? submit button <form> tags: Opening/closing action attribute: action to take when form data is submitted <input>: empty tags (no closing tags) name attribute specifies identifier for element (like id) type attribute defines type of input <form> <input> <label> action="" type ="" 19

20 Possible values for the type attribute button checkbox color date datetime datetime-local file hidden image month number password radio range reset search submit tel text time url week 20

21 most 21

22 most Each paired with a <label> element, e.g. <label>your name (required):</label> Radio buttons (single selection) Checkboxes (multiple selections) <input type="submit" value="submit" /> or <button type="submit">go (with button)</button> type= " sign) type="url" (requires valid) Drop-down menu <select> 22

23 Markup used (partial shown) <form action="response_demo.py"> <br/> <label for="name">your name:</label> <input type="text" id="name" name="name"> <br/> <label for=" ">your (required):</label> <input type=" " id=" " name=" "> <br/> <label for="webpage">url of your webpage:</label> <input type="url" id="webpage" name="webpage" autofocus > <br/> <label for="blurb">your favourite car:</label> <select id="blurb"> <option value="volvo">volvo</option> <option value="saab">saab</option> <option value="mercedes">mercedes</option> <option value="audi">audi</option> </select> </form> 23

24 Markup used (partial shown) <form action="response_demo.py"> <br/> <label for="name">your name:</label> <input type="text" id="name" name="name"> <br/> Use line breaks <label> tags <label for=" ">your (required):</label> <input type=" " id=" " name=" "> <br/> <label for="webpage">url of your webpage:</label> <input type="url" id="webpage" name="webpage" autofocus > <br/> <label for="blurb">your favourite car:</label> <select id="blurb"> <option value="volvo">volvo</option> <option value="saab">saab</option> <option value="mercedes">mercedes</option> <option value="audi">audi</option> </select> </form> 24

25 Possible values for the type attribute button checkbox color date datetime datetime-local file hidden image month number password radio range reset search submit tel text time url week 25

26 Attributes of <form> tag Attribute accept-charset action autocomplete enctype Description Specifies the charset used in the submitted form (default: the page charset). Specifies an address (url) where to submit the form (default: the submitting page). Specifies if the browser should autocomplete the form (default: on). Specifies the encoding of the submitted data (default: is url-encoded). method <h1>form Example</h1> name novalidate target Specifies the HTTP method used when submitting the form (default: GET). Specifies a name used to identify the form (for DOM usage: document.forms.name). <form action="response_script.py" autocomplete="on" > <input type="text" name="lname" value="default text value" /> Specifies that the browser should not validate the form. <input type="text" name="fname" size="6" maxlength="10" /> <input type="submit" value="go!" /> </form> Specifies the target of the address in the action attribute (default: _self). 26

27 Autocomplete attribute Type s would result in some guesses made based on user s browse history 27

28 FYI, pattern: an input attribute (also new in HTML5) Offers more complex constraints pattern="[search_pattern]{number_of_times}" <form action="do_something.py"> <label>country code:</label> <input type="text" name="code" pattern="[a-za-z]{3}" title="3 letter country code"/> </form> CMPT 165 D1 (Fall 2015) 28 Reminder: renders as a tooltip

29 FYI, pattern: an input attribute (also new in HTML5) Offers more complex constraints pattern="[search_pattern]{number_of_times}" <form action="do_something2.py"> <label>your name:</label> <input type="text" name="fname" pattern="[a-za-z]{2,}" title="2 or more"/> </form> CMPT 165 D1 (Fall 2015) 29

30 More examples <form action="do_something.py"> <label>password:</label> <input type="password" name="pw" pattern=".{6,}" title="six or more characters" /> </form> CMPT 165 D1 (Fall 2015) 30

31 FYI, more examples <form action="do_something.py"> <label>password:</label> <input type="password" name="pw" pattern="(?=.*\d)(?=.*[a-z])(?=.*[a-z]).{8,}" title="must contain at least 1 number, 1 uppercase, and 1 lowercase letter, and at least 8 or more characters"> <label> </label> <input type=" " name=" " pattern="[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,3}$"> <input type="submit"> </form> CMPT 165 D1 (Fall 2015) 31

32 input:required Another pseudo-class state of an element CSS: to warn users input:required{ background-color: #faa; } CMPT 165 D1 (Summer 2015) 32

33 input:required Another pseudo-class state of an element CSS: to warn users /* another way */ input:required { outline: 1px red solid; color: red; } CMPT 165 D1 (Fall 2015) 33

34 Questions?

35 CMPT 165 Unit 8 - Part 2: Form processing Nov 26 th, 2015

36 Regular_webpage.html <h1>form Example</h1> Getting user input <form action="response_script.py"> <input type="text" name= lname" value="default text value" /> <input type="text" name= fname" size="6" maxlength="10" /> <input type="submit" value="go!" /> </form> Steps: 1. Markup for form (regular_webpage.html) 2. Specifies action to take when user click submits 3. When action is executed (response_script.py) Usually takes user input (form data) Provides feedback (i.e. generates dynamical markup accordingly) Interaction: User provides input form data generates output based on form data 36 form data CGI module Your script output

37 Regular_webpage.html Getting user input <h1>form Example</h1> <form action="response_script.py"> <input type="text" name="lname" /> <input type="text" name="fname" /> <input type="submit" value="go!" /> </form> form data Steps: 1. Markup for form (regular_webpage.html) 2. Specifies action to take when user click submits 3. When action is executed (response_script.py) Usually takes user input (form data) Provides feedback (i.e. generates dynamical markup accordingly) Interaction: User provides input form data generates output based on form data 37 CGI module Your script output

38 Regular_webpage.html Form-Script Data transfer <h1>form Example</h1> <form action="response_script.py"> <input type="text" name="lname" /> <input type="text" name="fname" /> <input type="submit" value="go!" /> </form> form data response_script.py CGI module import cgi fm = cgi.fieldstorage() lastname = fm.getvalue("lname") Your script firstname = fm.getvalue("fname") import myutils # use your E8 output print( myutils.get_standard_opening_markup() ) # form processing: simple feedback print( "<p>hello Mr. "+firstname + lastname + "</p>") print( CMPT 165 myutils.get_closing_markup()) D1 (Summer 2005) 38

39 Regular_webpage.html Form-Script Data transfer <h1>form Example</h1> <form action="response_script.py"> <input type="text" name="lname" /> <input type="text" name="fname" /> <input type="submit" value="go!" /> </form> form data response_script.py CGI module import cgi fm = cgi.fieldstorage() lastname = fm.getvalue("lname") Your script firstname = fm.getvalue("fname") import myutils # use your E8 output print( myutils.get_standard_opening_markup() ) # form processing: simple feedback print( "<p>hello Mr. "+firstname + lastname + "</p>") print( CMPT 165 myutils.get_closing_markup()) D1 (Summer 2005) 39 From your E8

40 Regular_webpage.html Form-Script Data transfer <h1>form Example</h1> <form action="response_script.py"> <input type="text" name="lname" /> <input type="text" name="fname" /> <input type="submit" value="go!" /> </form> form data response_script.py CGI module import cgi fm = cgi.fieldstorage() lastname = fm.getvalue("lname") Your script firstname = fm.getvalue("fname") import myutils # use your E8 output print( myutils.get_standard_opening_markup() ) # form processing: simple feedback print( "<p>hello Mr. "+firstname + lastname + "</p>") print( CMPT 165 myutils.get_closing_markup()) D1 (Summer 2005) 40 From your E8

41 Regular_webpage.html <h1>form Example</h1> Form-Script Data transfer <form action="response_script.py"> <input type="text" name="lname" /> <input type="text" name="fname" /> <input type="submit" value="go!" /> </form> response_script.py import cgi fm = cgi.fieldstorage() lastname = fm.getvalue("lname") firstname = fm.getvalue("fname") import myutils # use your E8 Loads the cgi module, usually under C:\Program Files\Python\Lib\cgi.py Returns an object with built-in function: getvalue(name_of_input_elem) print( myutils.get_standard_opening_markup() ) # form processing: simple feedback print( "<p>hello Mr. "+firstname + lastname + "</p>") form data CGI module Your script output print( CMPT 165 myutils.get_closing_markup()) D1 (Summer 2005) 41 From your E8

42 CGI module CMPT 165 D1 (Summer 2015) 42

43 Looking up modules in IDLE CMPT 165 D1 (Fall 2015) 43

44 <!DOCTYPE html> <html> <head> <title>checkbox Example</title> </head> <body > <p>please pick a colour:</p> <form action="process_chkbox.py" method="post"> <input type="checkbox" name="red" value="1"> Red colour<br> <input type="checkbox" name="green" value="1"> Green colour<br> <input type="checkbox" name="blue" value="1"> Blue colour<br> <input type="checkbox" name="gold" value="1"> Gold colour<br> <input type="submit"> </form> </body> </html>

45 print( """Content-Type: text/html <!DOCTYPE html> <head><title>checkbox processed</title></head><body> <h1>checkbox processed</h1> <p>you have selected these choices:<br/>""" ) # what is absolutely needed? import cgi # import module form=cgi.fieldstorage(); # module.function_name( arguments ) r= form.getvalue("red"); g= form.getvalue("green"); b= form.getvalue("blue"); gg= form.getvalue("gold"); if ( r!= None ): # if selected if ( int(r) == 1): # if value is 1 print( " - Red <br/>" ); if ( g!= None ): # if selected if (int(g) == 1): print( " - Green <br/>" ); # put other cases here print( "</p>" ); print( "</body></html>" )

46 Questions?

47 Programming essentials Variables Scope of variable Data Types Numeric Strings integer float Boolean Assignment (shorthand) Operations/Operator Misc. Arithmetic Concatenation Overloaded symbols Refining print statements Commenting Data objects: lists Collection of data items Indexing items Has built-in functions, e.g. str.lower() numbers.sort() Program flow Test conditions Numeric comparisons String comparisons Control: If, elif, else General objects Construct for data + functions Why? code reuse via modules CMPT 165 D1 (Fall 2015) 47 Reminder: Make sure you know each term on this slide Modules Modules you defined (E8+E9) Built-in modules, e.g. CGI random (A3) datetime (A3) Load via import Functions Data: Input/Output (I/O) Process Built-in functions: len() sum() type int, float, str range(0,10)

48 Data types 1. Numeric Integer, e.g. With no fractional component, e.g. {0,1,2,3,4, } Floating point With fractional component, e.g. between 0 and 5: [0,5], e.g Strings >>> a_str = "c"; >>> another_str = "cccccc"; 3. Boolean 2 values only: True or False >>> z = (1 >= 1) True >>> z = (1 > 1) False 4. CMPT 165 D1 (Fall 2015) 48

49 Working with different data types >>> a_str = "c"; >>> a_num = 3; >>> a_num + a_str Arguments to operator e.g. z= a + b Traceback (most recent call last): File "<pyshell#35>", line 1, in <module> a+b TypeError: unsupported operand type(s) for +: 'int' and 'str' A logical error (in this case, unreasonable to combine them in a single statement) except, e.g. >>> print( a_num,a_str ) 3 c >>> type(a_num) <type 'int'> >>> type(a_str) <type 'str'> CMPT 165 D1 (Fall 2015) 49

50 Converting between types >>> # string to string >>> a_str ="100" >>> z = ("%s" % a_str) >>> # How to convert number to string? >>> x = >>> z = ("%s" % x) >>> # How to convert string to integer? >>> x = int(a_str) >>> # How to convert string to float? >>> a_float="1.55" >>> print( int(a_float) ) ValueError: invalid literal for int() with base 10 >>> print( float(a_float) ) 50

51 Lab 9 import cgi; fm=cgi.fieldstorage(); # Retrieve form data name=fm.getvalue("f_name") year=fm.getvalue("f_year") # convert string type to numeric type age= int(year) salutation=fm.getvalue("f_salutation") cmpt=fm.getvalue("f_cmpt") import myutils print( myutils.get_o_markup() ) # rest of solution here # test cases print( myutils.get_c_markup() ) CMPT 165 D1 (Summer 2015) 51

52 Programming essentials Variables Scope of variable Data Types Numeric Strings integer float Boolean Assignment (shorthand) Operations/Operator Misc. Arithmetic Concatenation Overloaded symbols Refining print statements Commenting Data objects: lists Collection of data items Indexing items Has built-in functions, e.g. str.lower() numbers.sort() Program flow Test conditions Numeric comparisons String comparisons Control: If, elif, else General objects Construct for data + functions Why? code reuse via modules CMPT 165 D1 (Fall 2015) 52 Reminder: Make sure you know each term on this slide Modules Modules you defined (E8+E9) Built-in modules, e.g. CGI random (A3) datetime (A3) Load via import Functions Data: Input/Output (I/O) Process Built-in functions: len() sum() type int, float, str range(0,10)

53 Programming essentials Variables Scope of variable Data Types Numeric Strings integer float Boolean Assignment (shorthand) Operations/Operator Misc. Arithmetic Concatenation Overloaded symbols Refining print statements Commenting Data objects: lists Collection of data items Indexing items Has built-in functions, e.g. str.lower() numbers.sort() Program flow Test conditions Numeric comparisons String comparisons Control: If, elif, else General objects Construct for data + functions Why? code reuse via modules CMPT 165 D1 (Fall 2015) 53 Reminder: Make sure you know each term on this slide Modules Modules you defined (E8+E9) Built-in modules, e.g. CGI random (A3) datetime (A3) Load via import Functions Data: Input/Output (I/O) Process Built-in functions: len() sum() type int, float, str range(0,10) loops!

54 Lots of repetitions? E.g. Loops A table of 1000 products to sell An address book of your 100 wonderful friends The A2 surveys: to be shown if there is time Loops come to rescue! Two types of loops useful for A3 For loop While loop

55 Loops >>> Names = ['Dave', 'Sam', 'Bella', 'Paul'] >>> for a_name in Names: print( "%s" % a_name ) Dave Sam Bella Paul How many lines of code? But you need to write 2 lines only! Q: What happened really? This same line of code executed multiple times print( "%s" % a_name ) Repeated n=4 times. How? n = len( Name ) In each iteration, a_name is changed In iteration 0, this is executed: a_name=names[0] # print( Names[1] )?? In iteration 1, this is executed: a_name=names[1] # print( Names[1] )?? In iteration n, generalize this as: a_name=names[n] # print( Names[n] )??

56 Loops >>> Numbers = [1,2,3,4,5]; sum=0 >>> for a_num in Numbers: sum = sum + a_num >>> print( sum ) 15 Q: What happened really? This same line of code executed multiple times sum = sum + a_num Repeated n=5 times. How? n = len( a_num ) In each iteration, a_num is changed In iteration 0, this is executed: a_num=numbers[0] # print( Numbers[1] )?? How many lines of code? But you need to write 2 lines only! In iteration 1, this is executed: a_num=numbers[1] # print( Numbers[1] )?? In iteration n, generalize this as: a_num=numbers[n] # print( Numbers[n] )??

57 Loops >>> Numbers = [1,2,3,4,5]; sum=0 >>> for a_num in Numbers: sum = sum + a_num >>> print( sum ) 15 >>> Numbers = [1,2,3,4,5]; sum=0 >>> for a_num in Numbers: sum = sum + a_num # try adding this to understand loops: print( sum ) How many lines of code? But you need to write 2 lines only!

58 Shopping cart example >>> age=18 >>> cost_of_items=[3,1,1,5,10] >>> cost_of_purchase=sum(cost_of_items) >>> print cost_of_purchase 20 >>> cost_of_purchase=sum(cost_of_items)*1.1 >>> print cost_of_purchase 22 >>> if (age>=65): cost_of_purchase*= 0.9 >>> print cost_of_purchase 19.8 >>> if len(cost_of_items)>10: cost_of_purchase*= 0.9 >>> print cost_of_purchase 19.8 >>> if (age>=65) and len(cost_of_items)>10 : cost_of_purchase*= 0.8 CMPT 165 D1 (Summer 2015) 58 Reminder: Built-in function for length (i.e. number of items in list)

59 Without built-in sum function? >>> cost=[3,1,1,5,10] >>> # calculate sum >>> total=0; >>> index=0 >>> print( cost[index] ) 3 >>> total+=cost[index] >>> index=1 >>> total+=cost[index] >>> index=2 >>> total+=cost[index] >>> index=3 >>> total+=cost[index] >>> index=4 >>> total+=cost[index] >>> index=5 >>> total+=cost[index] IndexError: list index out of range >>> cost=cost_of_items >>> # calculate sum >>> total=0 >>> index=0 >>> >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> if index < len(cost) total+=cost[index] index+=1 >>> if index <= len(cost)#? total+=cost[index] CMPT 165 D1 (Summer 2015) 59

60 Without built-in sum function? What do you notice? Some statements: repeated stop repeating based on some criterion Variable total is temporary place holder for total Which variables must be assigned (initialized)? cost_of_items total index CMPT 165 D1 (Fall 2015) >>> cost=cost_of_items >>> # calculate sum >>> total=0 >>> index=0 >>> >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> if index < len(cost) total+=cost[index] index+=1 60

61 Without built-in sum function? What do you notice? Some statements: repeated stop repeating based on some criterion Variable total is temporary place holder for total Which variables must be assigned (initialized)? cost_of_items total index CMPT 165 D1 (Fall 2015) >>> cost=cost_of_items >>> # calculate sum >>> total=0 >>> index=0 >>> >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> if index < len(cost) total+=cost[index] index+=1 61

Governing program flow # initialization while (True): # repeated statements # repeated statements # repeated statements cost=[5,12,3,14] total=0 index=0 if index < len(cost) total+=cost[index]

62 Governing program flow # initialization while (True): # repeated statements # repeated statements # repeated statements cost=[5,12,3,14] total=0 index=0 if index < len(cost) total+=cost[index] index+=1 CMPT 165 D1 (Summer 2015) initialization Continuation criteria/criterion Iterative statements >>> cost=cost_of_items >>> # calculate sum >>> total=0 >>> index=0 >>> >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> if index < len(cost) total+=cost[index] index+=1 62

63 Program flow via while loop # initialization while (True): # repeated statements # repeated statements # repeated statements cost=[5,12,3,14] total=0 index=0 if index < len(cost) total+=cost[index] index+=1 CMPT 165 D1 (Summer 2015) cost=[5,12,3,14] total=0 index=0 while (index < len(cost)): total+=cost[index] index+=1 63

64 Program flow via while loop >>> cost=cost_of_items >>> # calculate sum >>> total=0 >>> index=0 >>> >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> index+=1 >>> total+=cost[index] >>> if index < len(cost) total+=cost[index] index+=1 CMPT 165 D1 (Summer 2015) cost=[5,12,3,14] total=0 index=0 while (index < len(cost)): total+=cost[index] index+=1 64

65 Loops # initialization while (True): # repeated statements # repeated statements # repeated statements # initialization for sequence_governing_flow: # repeated statements # repeated statements # repeated statements Sequence of statements: index=0 index=1 index=2 index=3 index in [0,1,2,3] CMPT 165 D1 (Fall 2015) Tells Python how variable changes cost=[5,12,3,14] total=0 index=0 while (index < len(cost)): total+=cost[index] index+=1 total=0; index=0 for index in [0,1,2,3]: 65 total+=cost[index]

66 Putting all together cost=[5,12,3,14] total=0 Loops for index in range(0,len(cost)): total+=cost[index] cost=[5,12,3,14] total=0 index=0 while (index < len(cost)): total+=cost[index] index+=1 CMPT 165 D1 (Fall 2015) 66

67 Practice # Q1) what does this do? x = 1 while (x<10): x += 1 Why bother with loops? print "%d" % x # Q2) what does this do? Names = ['Dave', 'Sam', 'Bella', 'Paul'] for a_name in Names: print "%s" % a_name CMPT 165 D1 (Fall 2015) 67

68 Loops make repetitive tasks easy and quick Parts of the code used shown next slide FYI only CMPT 165 D1 (Fall 2015) 68

69 69 Questions?

ATTENTION. Read my today about the A2 design surveys + note the due dates of these too! Don t forget to go through the Study Guide as well!

ATTENTION. Read my today about the A2 design surveys + note the due dates of these too! Don t forget to go through the Study Guide as well! ATTENTION In these slides: Review + introduced to: for, while loop Slides #23: range(a,b,c) #another built-in function Slides #28-32: Loops to help you get the bonus for A3 (make sure you understand every