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Python Enhancement Proposals

PEP 222 – Web Library Enhancements

A.M. Kuchling <amk at>
Standards Track

Table of Contents


This PEP proposes a set of enhancements to the CGI development facilities in the Python standard library. Enhancements might be new features, new modules for tasks such as cookie support, or removal of obsolete code.

The original intent was to make improvements to Python 2.1. However, there seemed little interest from the Python community, and time was lacking, so this PEP has been deferred to some future Python release.

Open Issues

This section lists changes that have been suggested, but about which no firm decision has yet been made. In the final version of this PEP, this section should be empty, as all the changes should be classified as accepted or rejected. We should not be told to create our own subclass just so we can handle file uploads. As a practical matter, I have yet to find the time to do this right, so I end up reading’s temp file into, at best, another file. Some of our legacy code actually reads it into a second temp file, then into a final destination! And even if we did, that would mean creating yet another object with its __init__ call and associated overhead. Currently, query data with no = are ignored. Even if keep_blank_values is set, queries like ...?value=&... are returned with blank values but queries like ...?value&... are completely lost. It would be great if such data were made available through the FieldStorage interface, either as entries with None as values, or in a separate list.

Utility function: build a query string from a list of 2-tuples

Dictionary-related utility classes: NoKeyErrors (returns an empty string, never a KeyError), PartialStringSubstitution (returns the original key string, never a KeyError)

New Modules

This section lists details about entire new packages or modules that should be added to the Python standard library.

  • : A new module adding support for the FastCGI protocol. Robin Dunn’s code needs to be ported to Windows, though.

Major Changes to Existing Modules

This section lists details of major changes to existing modules, whether in implementation or in interface. The changes in this section therefore carry greater degrees of risk, either in introducing bugs or a backward incompatibility.

The module would be deprecated. (XXX A new module or package name hasn’t been chosen yet: ‘web’? ‘cgilib’?)

Minor Changes to Existing Modules

This section lists details of minor changes to existing modules. These changes should have relatively small implementations, and have little risk of introducing incompatibilities with previous versions.

Rejected Changes

The changes listed in this section were proposed for Python 2.1, but were rejected as unsuitable. For each rejected change, a rationale is given describing why the change was deemed inappropriate.

  • An HTML generation module is not part of this PEP. Several such modules exist, ranging from HTMLgen’s purely programming interface to ASP-inspired simple templating to DTML’s complex templating. There’s no indication of which templating module to enshrine in the standard library, and that probably means that no module should be so chosen.
  • Allowing a combination of query data and POST data. This doesn’t seem to be standard at all, and therefore is dubious practice.

Proposed Interface

XXX open issues: naming convention (studlycaps or underline-separated?); need to look at the cgi.parse*() functions and see if they can be simplified, too.

Parsing functions: carry over most of the parse* functions from

# The Response class borrows most of its methods from Zope's
# HTTPResponse class.

class Response:
    status: HTTP status code to return
    headers: dictionary of response headers
    body: string containing the body of the HTTP response

    def __init__(self, status=200, headers={}, body=""):

    def setStatus(self, status, reason=None):
        "Set the numeric HTTP response code"

    def setHeader(self, name, value):
        "Set an HTTP header"

    def setBody(self, body):
        "Set the body of the response"

    def setCookie(self, name, value,
                  path = '/',
                  comment = None,
                  domain = None,
                  max-age = None,
                  expires = None,
                  secure = 0
        "Set a cookie"

    def expireCookie(self, name):
        "Remove a cookie from the user"

    def redirect(self, url):
        "Redirect the browser to another URL"

    def __str__(self):
        "Convert entire response to a string"

    def dump(self):
        "Return a string representation useful for debugging"

    # XXX methods for specific classes of error:serverError,
    # badRequest, etc.?

class Request:


    XXX should these be dictionaries, or dictionary-like objects?
    .headers : dictionary containing HTTP headers
    .cookies : dictionary of cookies
    .fields  : data from the form
    .env     : environment dictionary

    def __init__(self, environ=os.environ, stdin=sys.stdin,
                 keep_blank_values=1, strict_parsing=0):
        """Initialize the request object, using the provided environment
        and standard input."""

    # Should people just use the dictionaries directly?
    def getHeader(self, name, default=None):

    def getCookie(self, name, default=None):

    def getField(self, name, default=None):
        "Return field's value as a string (even if it's an uploaded file)"

    def getUploadedFile(self, name):
        """Returns a file object that can be read to obtain the contents
        of an uploaded file.  XXX should this report an error if the
        field isn't actually an uploaded file?  Or should it wrap
        a StringIO around simple fields for consistency?

    def getURL(self, n=0, query_string=0):
        """Return the URL of the current request, chopping off 'n' path
        components from the right.  Eg. if the URL is
        "", n=2 would return
        "".  Does not include the query string (if

    def getBaseURL(self, n=0):
        """Return the base URL of the current request, adding 'n' path
        components to the end to recreate more of the whole URL.

        Eg. if the request URL is
        "", n=0 would return
        "", and n=2 "".

        Returned URL does not include the query string, if any.

    def dump(self):
        "String representation suitable for debugging output"

    # Possibilities?  I don't know if these are worth doing in the
    # basic objects.
    def getBrowser(self):
        "Returns Mozilla/IE/Lynx/Opera/whatever"

    def isSecure(self):
        "Return true if this is an SSLified request"

# Module-level function
def wrapper(func, logfile=sys.stderr):
    Calls the function 'func', passing it the arguments
    (request, response, logfile).  Exceptions are trapped and
    sent to the file 'logfile'.
    # This wrapper will detect if it's being called from the command-line,
    # and if so, it will run in a debugging mode; name=value pairs
    # can be entered on standard input to set field values.
    # (XXX how to do file uploads in this syntax?)


Last modified: 2023-09-09 17:39:29 GMT