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ASP and Python

How Python integrates w/ASP


Active Server Pages has been a useful addition to Microsoft's Web strategy. Because of the language neutral nature of COM, any language that is capable of "Active X" (meaning COM) scripting can integrate with it. Python, with it's excellent COM support, is one of those languages. When you install it, by default, it is not setup for the ASP enviroment with IIS. If you look at the html documentation in: C:\\Program Files\\Python\\win32com\\HTML\\index.html at the bottom of the page you'll see 'Active X Scripting Demos'. If you then click on that it will describe how to register the engire. Essentially, there is a program called pyscript.py in: C:\\Program Files\\Python\\win32comext\\axscript\\client and if you run that it should register python for the ASP environment.


Microsoft typically positions vbscript in the IIS role. Vbscript is adequate for many tasks, but is a very simplified language. Python is a very rich and powerful language offering things like true exception handleing, OOP style programming, excellent win32 access, easy persistence w/pickle, etc. And, being multi-platform, you can leverage the language in other web environments. You will also find many ASP code examples in Vbscript are easily converted into python. There is a slight difference with setting values with Application and Session Objects. In cases where you'd see: Session('Key')= TheValue, you'd translate to Session.SetValue('Key', TheValue) for python. This is because vbscript makes it look like you are assigning something to a function call which python does not support.


Another thing ASP allows you to do is to mix code and HTML. Thus, you need some way to tell the server that the following is code. Since python is not used by default, you need to set your page to use it. You can do that by having the first line say: <%@ LANGUAGE =Python%>. Then after that point, anything between '<%' and '%>' delimeters will run as python code. Everything else will be treated as HTML. It is important to note that a python loop ends in the python block -- they don't extend past intervening html to the next block. For me that normally isn't an issue, since I do not like mixing code and html. Prefering a clean split of code and html, I generally generate webpages using templates all in python w/HTMLgen. Take a look at: http://www.python.org/topics/web/HTML.html for available resources w/HTML. An very basic page would look like:

Example

Basic Python ASP page:

<%@ LANGUAGE = Python%>

<HTML>

<head></head>

<body>



<h1>Querying database</h1>

<%

#do some python stuff here

#import libraries, etc.

for i in query_database():

	Response.Write('output of results converted to a string')



%>

</body>

</html>
If you use HTMLgen's template, then it could look like:

<%@ LANGUAGE = Python%>



<%



#notice no raw HTML at all.  We instead use a template html file

#generated however you want (perhaps frontpage) that substitutes

#anything delimeted by {} for output from our python.  In this case

#text {mid} in the template is substituted for results.



import HTMLgen

import HTMLcolors



results='<h1>Querying database</h1>'

for i in query_database():

	results=results+str(i)



######################

#Here we are using a template dictionary

#to substitute the text {mid} found in the template file

#for results

T=HTMLgen.TemplateDocument(/path/template_file.html)

T.substitutions['mid']=results  # here is where our results went!!

webpage=str(T)

Response.Write(webpage)

%>
For one page this is overkill. However, for developing many pages, something like this allows you to ignore the grunt work of making pages and helps to keep them consistent. HTMLgen also gives you other useful tools worth looking into.


The ASP model has several 'collection' objects: Request, Response, Session, Application, and ObjectContext. The Request collection has things like data returned from web forms(GET or POST) and environment variables. The Response object is the opposite of the Request object it deals with sending data back to the client, since you cannot do a simple 'print'. Next, the Application collection allows programs to globally store/share information for your site. The Session object allows one to store per-user state. And, finally the Objectcontext object is for use with MTS. We'll focus on the basics, Request and Response.


Typically, you can treat these objects like simple versions of a python dictionary or list. A good way to get an idea of what they have is to print out their entire contents. Here is a simple function that converts your server (environment) variables into a python dictionary:

def getenv ():

	d_env={} #initialize dictionary

	for key in Request.ServerVariables:

		d_env[key]=str(Request.ServerVariables(key))

	return d_env
Request.ServerVariables responds to the python operator 'in' by returning a list. And, it can also take a key and return it's value. You notice the value is converted into a string, so it can be treated like a python string.


For a more complicated example, here is a python function that converts the Request.Form or Request.Querystring objects into a python dictionary. This would be a function you'd use to get back data from a form. It returns either the entire Request Collection as a python dictionary, a subset if you provide a list of keys, or a single value, if you provide a single key.


Get Request collection - 3 different ways to get Request data

def getdata (keys=''):

	'''

] possible ways to call this function:

	value=getdata('key')

	dict=getdata(('key1','key2')) #get subset

	dict=getdata() #return everything

	It assumes you don't have the same key for

	GET and POST methods

	'''

	import types

	key_type=type(keys)

	d_data={} #initialize dictionary

	if keys=='': #if they don't supply keys then return everything

		for key in Request.Form:

			d_data[key]=Request.Form(key)

		for key in Request.QueryString:

			d_data[key]=Request.QueryString(key)

		return d_data

	elif key_type == types.StringType: #if they provide a single string

		value=Request.Form(keys)

		if (value != 'None') and (str(value) == 'None'):

			return Request.QueryString(keys)

		else:

			return value

	#if they provide a list then return a dictionary with all the key/values

	elif key_type == types.TupleType or key_type == types.ListType:

		for key in keys:

			value=Request.Form(key)

			#now check if the data was empty, if so look at QueryString

			if (value != 'None') and (str(value) == 'None'):

				value=Request.QueryString(key)

			data[key]=value

		return d_data
To print out this data you will need to use the Response object which accepts python strings. A simple: Response.Write(str(d_data)) would suffice. A better looking way would be to do something like:

for pair in d_data.items():

	Response.Write(pair[0]+':'+pair[1]+'<br>')
Notice the adding of <br> to have a line break for each pair. If you want it more fancy you can convert it to table output.


HTMLgen can help with it's Table object:

Table=HTMLgen.Table('Key/Value pairs for Response object') #title

Table.heading=('Key','Value')

for pair in d_data.items() #get each key/val pair

  Table.body.append(list(pair))  #takes a list of lists

				 #[ [key1,val1], [key2,val2]]

				 #one pair for every table row

Response.Write(str(Table))
HTMLgen deserves an entire article to itself. You can use it to write web forms and manage other HTML elements. As a final example, here is a simple ASP application that uses the functions written above and a simple HTMLgen web form to spit data back. The typical idiom w/HTMLgen is to create a web object like a form and append things to it. In the code below, I append a textbox, radio buttons, and a checkbox.

<%@ LANGUAGE = Python%>



<%

from HTMLgen import *

from HTMLcolors import *

#import the file which has getenv and getdata from above



d_env=getenv() #get environment variables



#create a simple default document

webpage = SimpleDocument(title = 'Bedrock Housing')



#create form and append elements to it

F=Form(d_env['URL'])

F.append(Heading(1,'Rock Housing'))

F.append('What Street:',BR())

F.append( Input(type='text',name='street',size=30),BR())



F.append('Select your house type:',BR())

types=('limestone','granite','marble')

for i in types:

	F.append(Input(type='radio',name='house_type',rlabel=i,value=i),BR())

F.append('Select special features:',BR())



features=('stone roof','dishwasher','door bell')

for i in features:

	F.append(Input(type='checkbox',name='features',rlabel=i,value=i),BR())

#done with web form, now append it

webpage.append(F)

#get the data the user entered and return it

results=getdata() #get everything

webpage.append(str(results))

Response.Write(str(webpage))
Have a great time with programming with python! 

John Nielsen   nielsenjf@my-deja.com