As we write them the notes become available by reloading this page in real time. 

Designing a multi-screen application (a finite state machine). 

-bash-3.2$ javac Story.java 
-bash-3.2$ java Story
20.0
30.0
5.0
-bash-3.2$ cat Story.java 
class Account {
  double balance;
  Account(double balance) {
    this.balance = balance; 
  }
  double report() {
    return this.balance;
  }
  void deposit(double amount) {
    this.balance += amount; 
  }   
}

class Story {
  public static void main(String[] args) {
    Account a = new Account(20); 
    System.out.println(a.report());
    a.deposit(10);
    System.out.println(a.report());
    a.deposit(-25);
    System.out.println(a.report());
  } 
}
-bash-3.2$ 

Now let's do the same in Python. 

class Account(object):
    def __init__(self, initial):
        self.balance = initial
    def deposit(self, amount):
        self.balance += amount
    def report(self):
        return self.balance

def main():
    a = Account(10)
    print a.report()
    a.deposit(20)
    print a.report()
    a.deposit(-5)
    print a.report()
        
Now let's use this for CGI. 

I will make screens into independent units (like players). 

As a coach I train a certain behavior in them, then let them play. 

So I'll be using an Object-Oriented Approach to this. 

-bash-3.2$ cat main
#!/usr/bin/python

print "Content-type: text/html\n\nHowdy"
-bash-3.2$ ls -ld main
-rwx------ 1 dgerman faculty 60 Apr 21 13:51 main
-bash-3.2$ 

------------------------------------------------------------------

-bash-3.2$ ls -ld *
-rwx------ 1 dgerman faculty 111 Apr 21 13:58 main
-rw-r--r-- 1 dgerman faculty 247 Apr 21 13:56 Parser.py
-rw-r--r-- 1 dgerman faculty 478 Apr 21 13:58 Parser.pyc
-bash-3.2$ cat main
#!/usr/bin/python

import Parser

message = Parser.data["message"]

print """
Message is: %s
""" % (message)


-bash-3.2$ cat Parser.py
import cgi

print "Content-type: text/html\n\n"

input = cgi.FieldStorage()

data = {}

for name in ("message", "n1", "n2", "correct", "total", "answer"):
  if input.has_key(name): 
    data[name] = input[name].value
  else:
    data[name] = ""


-bash-3.2$ 

-----------------------------------------------------------

-bash-3.2$ more Parser.py main
::::::::::::::
Parser.py
::::::::::::::
import cgi

print "Content-type: text/html\n\n"

input = cgi.FieldStorage()

data = {}

for name in ("source", "n1", "n2", "correct", "total", "answer"):
  if input.has_key(name): 
    data[name] = input[name].value
  else:
    data[name] = ""


::::::::::::::
main
::::::::::::::
#!/usr/bin/python

import Parser

class One(object):
  def show(self): 
    print """
<form>
This is Screen One. <p> 
Press <input type=submit value="Proceed"> to move on. 
</form> 
"""

class Two(object): 
  pass

source = Parser.data["source"]

if source in ("One", "Two", "Three", "Four"):
  pass
else:
  screen = One()
  screen.show()












-bash-3.2$

---------------------------------------------------------

-bash-3.2$ more Parser.py main
::::::::::::::
Parser.py
::::::::::::::
import cgi

print "Content-type: text/html\n\n"

input = cgi.FieldStorage()

data = {}

for name in ("source", "n1", "n2", "correct", "total", "answer"):
  if input.has_key(name): 
    data[name] = input[name].value
  else:
    data[name] = ""


::::::::::::::
main
::::::::::::::
#!/usr/bin/python

import Parser

class One(object):
  def show(self): 
    print """
<form>
This is Screen One. <p> 
Press <input type=submit value="Proceed"> to move on. 
<input type=hidden name=source value=One> 
</form> 
"""
  def finalize(self):
    screen = Two()
    screen.show()

class Two(object): 
  def show(self): 
    print """
<form>
This is Screen Two. <p> 
Press <input type=submit value="Proceed"> to move on. 
<input type=hidden name=source value=Two> 
</form> 
"""
  def finalize(self):
    screen = Three()
    screen.show()

class Three(object): 
  def show(self): 
    print """
<form>
This is Screen Three. <p> 
Press <input type=submit value="Proceed"> to move on. 
<input type=hidden name=source value=Three> 
</form> 
"""

source = Parser.data["source"]

if source in ("One", "Two", "Three", "Four"):
  screen = eval(source + "()")
  screen.finalize()
else:
  screen = One()
  screen.show()


------------------------------------------------------------