Web Interfaces. the web server Apache processing forms with Python scripts Python code to write HTML

Size: px

Start display at page:

Download "Web Interfaces. the web server Apache processing forms with Python scripts Python code to write HTML"

Victor Walker
5 years ago
Views:

1 Web Interfaces 1 Python Scripts in Browsers the web server Apache processing forms with Python scripts Python code to write HTML 2 Web Interfaces for the Determinant dynamic interactive forms passing data between forms computing the determinant 3 Cookies storing information about a client encryption with secure hash algorithm MCS 507 Lecture 27 Mathematical, Statistical and Scientific Software Jan Verschelde, 29 October 2012 Scientific Software (MCS 507) web interfaces 29 October / 41

2 Web Interfaces 1 Python Scripts in Browsers the web server Apache processing forms with Python scripts Python code to write HTML 2 Web Interfaces for the Determinant dynamic interactive forms passing data between forms computing the determinant 3 Cookies storing information about a client encryption with secure hash algorithm Scientific Software (MCS 507) web interfaces 29 October / 41

3 the web server Apache Apache is an open source web server, OS independent. Although named in honor of the Native American tribe, Apache makes a cute pun on a patchy web server with web site at Python often processes web forms we can call Python scripts from a browser give our programs a web interface make software available via the web. localhost = Scientific Software (MCS 507) web interfaces 29 October / 41

4 Running Apache We will demonstrate on a Mac OS X Apache is already installed, verify launching a browser with as address. 2 Select Sharing from the System Preferences and check Web Sharing to allow users of other computers to view webpages on this computer. 3 Instead of public_html, the Sites directory is where Mac users store their web pages. 4 Instead of /var/www/cgi-bin, CGI scripts are in /Library/WebServer/CGI-Executables. CGI = Common Gateway Interface, is set of protocols through which applications interact with web servers. Scientific Software (MCS 507) web interfaces 29 October / 41

$/usr/bin/python print "Content-Type: text/plain\n\n" print "Python works" and is in /Library/WebServer/CGI-Executables.$

5 Python works The script python_works.py contains 3 lines: #!/usr/bin/python print "Content-Type: text/plain\n\n" print "Python works" and is in /Library/WebServer/CGI-Executables. Scientific Software (MCS 507) web interfaces 29 October / 41

6 Web Interfaces 1 Python Scripts in Browsers the web server Apache processing forms with Python scripts Python code to write HTML 2 Web Interfaces for the Determinant dynamic interactive forms passing data between forms computing the determinant 3 Cookies storing information about a client encryption with secure hash algorithm Scientific Software (MCS 507) web interfaces 29 October / 41

7 showing a form The HTML in show_form.html brings The word hello is entered by the user. Pressing submit activates a Python script. Scientific Software (MCS 507) web interfaces 29 October / 41

8 processing a form Pressing submit brings up a new web page. The script process_form.py gets the word and prints one line into the browser window. Scientific Software (MCS 507) web interfaces 29 October / 41

9 code in show_form.html <html> <head> <title> MCS 507 Lec 27: show a form </title> </head> <body> <form action= " <b>enter a word:</b> <input type="text" name="word" size ="10"> <input type="submit" value="submit word"> </form> </body> </html> Scientific Software (MCS 507) web interfaces 29 October / 41

10 code in process_form.py #!/usr/bin/python import cgi form = cgi.fieldstorage() print "Content-Type: text/plain\n" try: w = form[ word ].value s = your word is s = s + \" + w + \" print s except KeyError: print "please enter a word" Scientific Software (MCS 507) web interfaces 29 October / 41

11 Web Interfaces 1 Python Scripts in Browsers the web server Apache processing forms with Python scripts Python code to write HTML 2 Web Interfaces for the Determinant dynamic interactive forms passing data between forms computing the determinant 3 Cookies storing information about a client encryption with secure hash algorithm Scientific Software (MCS 507) web interfaces 29 October / 41

12 forms in Python scripts writing HTML What we did before: 1 Form element in HTML page triggers action. 2 Action triggered by submit button is defined by a Python script. Advantage/disadvantage: + Separate HTML layout and actions. Submit brings up a new page each time. Scientific Software (MCS 507) web interfaces 29 October / 41

13 showing & processing forms At first, the script show_process_form.py shows Then the user fills in hello and submits. Scientific Software (MCS 507) web interfaces 29 October / 41

14 after submit Scientific Software (MCS 507) web interfaces 29 October / 41

15 printing a header #!/usr/bin/python import cgi def PrintHeader(title): """ writes title and header of page """ print """Content-type: text/html <html> <head> <title>%s</title> </head> <body>""" % title PrintHeader("MCS 507 Lec27: forms") Scientific Software (MCS 507) web interfaces 29 October / 41

16 printing a form The script show_process_form.py continues: print """ <form method = "post" method = "show_process_form.py"> <b>enter a word:</b> <input type = "text" name = "word"> <input type = "submit" value = "submit word"> </form>""" form = cgi.fieldstorage() if form.has_key("word"): print """<p>your word is <em>%s</em></p> """ % form["word"].value print "</body></html>\n" Scientific Software (MCS 507) web interfaces 29 October / 41

17 Web Interfaces 1 Python Scripts in Browsers the web server Apache processing forms with Python scripts Python code to write HTML 2 Web Interfaces for the Determinant dynamic interactive forms passing data between forms computing the determinant 3 Cookies storing information about a client encryption with secure hash algorithm Scientific Software (MCS 507) web interfaces 29 October / 41

18 prompting for a dimension The default value is set at 2. After the user changes it to 3, and hits submit... Scientific Software (MCS 507) web interfaces 29 October / 41

19 prompting for a matrix Scientific Software (MCS 507) web interfaces 29 October / 41

20 filling in values Scientific Software (MCS 507) web interfaces 29 October / 41

21 computing the determinant Scientific Software (MCS 507) web interfaces 29 October / 41

22 Web Interfaces 1 Python Scripts in Browsers the web server Apache processing forms with Python scripts Python code to write HTML 2 Web Interfaces for the Determinant dynamic interactive forms passing data between forms computing the determinant 3 Cookies storing information about a client encryption with secure hash algorithm Scientific Software (MCS 507) web interfaces 29 October / 41

23 script for web determinant The script is a sequence of two forms: 1 we ask for the dimension of the matrix The dimension is then used to generate a table of input elements to give the entries of the matrix. 2 we ask for the entries of the matrix The second form is processed by the same script. The action of this form brings up a new page with the matrix and the determinant. The dimension is passed from one form to the other through an input element. Scientific Software (MCS 507) web interfaces 29 October / 41

24 main() in web_det.py def main(): """ Web interface to compute a determinant. """ PrintHeader("compute determinant") form = cgi.fieldstorage() if not form.has_key("dim"): AskDimension() else: n = int(form["dim"].value) AskMatrix(n) print "</body></html>\n" Scientific Software (MCS 507) web interfaces 29 October / 41

25 default values def AskDimension(): """ form to enter the dimension """ print """<form method = "post" action = "web_det.py"> <p> Give dimension: <input type = "text" name = "dim" size = 4 value = 2> <input type = "submit"> </p> </form>""" Scientific Software (MCS 507) web interfaces 29 October / 41

26 asking for a matrix def AskMatrix(n): """ form to enter an n-by-n matrix """ print """<form method = "post" action = "compute_det.py">""" print """The dimension: <input type = "text" name = "dim" size = 4 value = %d>""" % n print "<p>enter matrix :</p>" Scientific Software (MCS 507) web interfaces 29 October / 41

27 a table in a form print "<table>" for i in range(0,n): print "<tr>" for j in range(0,n): print """<td><input type = "text" name = %d,%d size = 4></td>""" % (i,j) print "</table>" print """<input type = "submit">""" print "</form>" The name of each input element is (i,j). Scientific Software (MCS 507) web interfaces 29 October / 41

28 Web Interfaces 1 Python Scripts in Browsers the web server Apache processing forms with Python scripts Python code to write HTML 2 Web Interfaces for the Determinant dynamic interactive forms passing data between forms computing the determinant 3 Cookies storing information about a client encryption with secure hash algorithm Scientific Software (MCS 507) web interfaces 29 October / 41

29 the script compute_det.py from numpy import matrix, zeros from numpy.linalg import det def Determinant(form,n): """ returns the determinant of the matrix available in the form """ A = zeros((n,n),float) for i in range(0,n): for j in range(0,n): info = "%d,%d" % (i,j) if form.has_key(info): A[i,j] = float(form[info].value) print "The matrix is" print A return det(a) Scientific Software (MCS 507) web interfaces 29 October / 41

30 the main function def main(): """ Web interface to compute a determinant. """ print "Content-type: text/plain\n" form = cgi.fieldstorage() if form.has_key("dim"): n = int(form["dim"].value) d = Determinant(form,n) print "The determinant :", d main() Scientific Software (MCS 507) web interfaces 29 October / 41

31 Web Interfaces 1 Python Scripts in Browsers the web server Apache processing forms with Python scripts Python code to write HTML 2 Web Interfaces for the Determinant dynamic interactive forms passing data between forms computing the determinant 3 Cookies storing information about a client encryption with secure hash algorithm Scientific Software (MCS 507) web interfaces 29 October / 41

32 Personalized Web Browsing Storing information about a client: 1 previous selections made passing data from one script to another 2 personal information identification and passwords 3 information from previous visits counting number of visits Potential applications: 1 customize displayed content 2 store encrypted password for fast access 3 personalized pricing... Scientific Software (MCS 507) web interfaces 29 October / 41

33 storing information about client Cookies are data stored by web server on client computer, managed by the browser. Using the Cookie module: >>> import Cookie >>> c = Cookie.SmartCookie() >>> c[ L ] = 27 >>> c[ date ] = Mon 29 Oct 2012 >>> print c Set-Cookie: L=27 Set-Cookie: date="mon 29 Oct 2012" Cookies are objects like dictionaries. Scientific Software (MCS 507) web interfaces 29 October / 41

34 Using Cookies Count number of times browser visited. Write a script to 1 retrieve cookie, initialize counter to zero, 2 or increment the value of counter by one, 3 and display counter value on the page. Script is cookie_counter.py. 1 in /Library/WebServer/CGI-Executables, 2 browser settings must accept cookies. Note: each browser has its own cookies. Scientific Software (MCS 507) web interfaces 29 October / 41

35 Running cookie_counter.py Scientific Software (MCS 507) web interfaces 29 October / 41

36 code for main() #!/Library/Frameworks/.../bin/python import Cookie, os def GetCookie(): """ Retrieves cookie, either initializes counter, or increments the counter by one. """ def main(): """ Retrieves a cookie and writes the value of counter to the page. """ c = GetCookie() print c print "Content-Type: text/plain\n" print "counter: %d" % c[ counter ].value Scientific Software (MCS 507) web interfaces 29 October / 41

37 code for GetCookie() def GetCookie(): """ Retrieves cookie, either initializes counter, or increments the counter by one. """ if os.environ.has_key( HTTP_COOKIE ): c = Cookie.Cookie(os.environ[ HTTP_COOKIE ]) else: c = Cookie.Cookie() if not c.has_key( counter ): c[ counter ] = 0 else: c[ counter ] = c[ counter ].value + 1 return c Scientific Software (MCS 507) web interfaces 29 October / 41

38 Web Interfaces 1 Python Scripts in Browsers the web server Apache processing forms with Python scripts Python code to write HTML 2 Web Interfaces for the Determinant dynamic interactive forms passing data between forms computing the determinant 3 Cookies storing information about a client encryption with secure hash algorithm Scientific Software (MCS 507) web interfaces 29 October / 41

39 secure hash algorithm We can use cookies for login names and passwords. If passwords are unencrypted, then insecure. Secure hash algorithm: 1 computationally infeasible to compute inverse is trapdoor function 2 very low collision rate very low chance that two different messages will generate the same key Server encrypts password before sending to client. Authentication by comparing encrypted passwords. Scientific Software (MCS 507) web interfaces 29 October / 41

40 using the hashlib module >>> message = this is me >>> import hashlib >>> h = hashlib.sha256() >>> h <sha256 HASH 0x7fede9bc5228> >>> h.update(message) >>> h.hexdigest() dd81cb79f11bedd77be0000f28e264e2c4b42376c76b891c7845b Scientific Software (MCS 507) web interfaces 29 October / 41

41 Summary + Exercises Apache and Python are the A and P in LAMP. 0 Verify that Apache runs on your computer. 1 Write a web interface to compute the greatest common divisor of two user given numbers. 2 Make an HTML form that prompts the user to enter a polynomial with integer coefficients in the variable x. The action in the form calls a script that uses SymPy to extract the vector of coefficients and the degree. 3 Extend the previous exercise to make a web interface for MPSolve (see Lecture 13). Homework due Friday 16 November at 10AM: exercises 1 and 3 of lecture 21; exercise 1 of lecture 22; exercise 2 of lecture 23; exercises 2 and 4 of lecture 24; exercises 1 and 2 of lecture 25; exercises 1 and 3 of lecture 26. Scientific Software (MCS 507) web interfaces 29 October / 41

Advanced CGI Scripts. personalized web browsing using cookies: count number of visits. secure hash algorithm using cookies for login data the scripts

Advanced CGI Scripts. personalized web browsing using cookies: count number of visits. secure hash algorithm using cookies for login data the scripts Advanced CGI Scripts 1 Cookies personalized web browsing using cookies: count number of visits 2 Password Encryption secure hash algorithm using cookies for login data the scripts 3 Authentication via