Begin by writing import cgi. Don't use from cgi import * - the module defines all sorts of names for its own use or for backward compatibility that you don't want in your namespace.
It's best to use the FieldStorage class. The other classes define in this module are provided mostly for backward compatibility. Instantiate it exactly once, without arguments. This reads the form contents from standard input or the environment (depending on the value of various environment variables set according to the CGI standard). Since it may consume standard input, it should be instantiated only once.
The FieldStorage instance can be accessed as if it were a Python dictionary. For instance, the following code (which assumes that the Content-type header and blank line have already been printed) checks that the fields name and addr are both set to a non-empty string:
form = cgi.FieldStorage() form_ok = 0 if form.has_key("name") and form.has_key("addr"): if form["name"].value != "" and form["addr"].value != "": form_ok = 1 if not form_ok: print "<H1>Error</H1>" print "Please fill in the name and addr fields." return ...further form processing here...
If the submitted form data contains more than one field with the same name, the object retrieved by form[key] is not a (Mini)FieldStorage instance but a list of such instances. If you expect this possibility (i.e., when your HTML form comtains multiple fields with the same name), use the type() function to determine whether you have a single instance or a list of instances. For example, here's code that concatenates any number of username fields, separated by commas:
username = form["username"] if type(username) is type(): # Multiple username fields specified usernames = "" for item in username: if usernames: # Next item -- insert comma usernames = usernames + "," + item.value else: # First item -- don't insert comma usernames = item.value else: # Single username field specified usernames = username.value
fileitem = form["userfile"] if fileitem.file: # It's an uploaded file; count lines linecount = 0 while 1: line = fileitem.file.readline() if not line: break linecount = linecount + 1
When a form is submitted in the ``old'' format (as the query string or as a single data part of type application/x-www-form-urlencoded), the items will actually be instances of the class MiniFieldStorage. In this case, the list, file and filename attributes are always None.