Python, CGI

1
Python, CGI

• November 23, Unit 8

2
So Far

• We can write programs in Python (in theory at
  least)
• Conditionals
• Variables
• While loops
• We can create a form for our web page
• Adding controls
• Now we need some way to take that form
  information and process it somehow

3
CGI

• Common Gateway Interface
• Its how we are going to pass information from
  our form to a web script
• In this case well be taking our form information
  and giving it to our Python script
• To use CGI in Python we have to include the CGI
  module

4
Accessing Form Information

• First, we must import the CGI module
• import cgi
• The next step is to load the form data into a
  variable in your Python script
• Well do this using the cgi.FieldStorage()
  function and assign it to some variable we create
• Ex. form cgi.FieldStorage()

5
Whats in the form Variable?

• The form variable will have all of the
  information stored in our HTML form
• Now we have to have a way to access the
  individual parts
• Each of our controls has a name attribute and a
  unique name
• This is how we are going to access the values in
  each part of the form

6
Accessing the Information

• When we want the value entered into a specific
  control, we have to know the name we gave it in
  the HTML
• The method of accessing its value is
• formname.value
• form is the name of the variable we assigned
  cgi.FieldStorage to (form cgi.FieldStorage)
• name is the value of name attribute in the HTML
  of the control
• .value gives us the value for that control

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Information Access, cont.

• If you specify a name that doesnt exist in your
  form, you will get a Key Error when you press
  your submit button
• The square brackets in the formname.value are
  used for accessing whats called a dictionary
• We are looking up in the dictionary called form
  the entry for name
• Each item in the dictionary will have a value
  associated with it

8
Using Values from a Form

• We can use the values from the form like we would
  any value returned by a function
• One thing to do is to assign it to a variable so
  that we can easily reuse it
• customerName formcustName.value
• phoneNumber int(formcustPhone.value
• All of the data stored in form will be a string
• If we want a number, we have to convert it using
  the (int) or (float) functions

9
Calling the CGI Script

• The ltformgt tag seems like it does nothing
• But remember that it has to have the action
  attribute
• When the user presses the submit button on the
  form, the script specified in the action
  attribute is called and can access the
  information stored in our HTML form
• Remember that the action attribute specifies the
  URL of the script we want to call

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Basics for a Form

• To add a form to our website requires two things
• The HTML form
• Some controls
• Submit Button
• The Python script to do something with that
  information
• Why ask for the information if we dont do
  something with it?

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In-Class Example

• Creating a simple form
• Using a Python script to output a new web page

12
Questions?

• Well be covering this more in-depth on Friday
  when we have internet access and we can actually
  see a demo