This example builds on the Gurl class from gurl.py in munki and creates a POST variant called Purl

purl.py

# Based on: https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/URLLoadingSystem/Tasks/UsingNSURLConnection.html#//apple_ref/doc/uid/20001836-SW5

from gurl import *
from Foundation import NSData, NSString

class Purl(Gurl):
    '''A POST variant of Gurl'''
    def initWithOptions_(self, options):
        '''Set up our Purl object'''
        # Inherit our basic setup from Gurl
        self = super(Purl, self).initWithOptions_(options)
        if not self:
            return
        # Now we add in our additional properties: body, content_type
        if options.get('content_type') is not None:
            self.additional_headers['Content-Type'] = options.get('content_type')
        self.body = options.get('body')
        return self

    def start(self):
        '''Start the connection'''
        # We're cloning Gurl's start and adding a section in the middle
        if not self.destination_path:
            self.log('No output file specified.')
            self.done = True
            return
        url = NSURL.URLWithString_(self.url)
        request = (
            NSMutableURLRequest.requestWithURL_cachePolicy_timeoutInterval_(
                url, NSURLRequestReloadIgnoringLocalCacheData,
                self.connection_timeout))
        if self.additional_headers:
            for header, value in self.additional_headers.items():
                request.setValue_forHTTPHeaderField_(value, header)
        # new POST-specific code
        request.setHTTPMethod_('POST')
        body_unicode = unicode(self.body)
        body_data    = NSData.dataWithBytes_length_(NSString.stringWithString_(body_unicode).UTF8String(), len(body_unicode.encode('utf-8')))
        request.setHTTPBody_(body_data)
        # end POST-specific
        # does the file already exist? See if we can resume a partial download
        if os.path.isfile(self.destination_path):
            stored_data = self.get_stored_headers()
            if (self.can_resume and 'expected-length' in stored_data and
                    ('last-modified' in stored_data or 'etag' in stored_data)):
                # we have a partial file and we're allowed to resume
                self.resume = True
                local_filesize = os.path.getsize(self.destination_path)
                byte_range = 'bytes=%s-' % local_filesize
                request.setValue_forHTTPHeaderField_(byte_range, 'Range')
        if self.download_only_if_changed and not self.resume:
            stored_data = self.cache_data or self.get_stored_headers()
            if 'last-modified' in stored_data:
                request.setValue_forHTTPHeaderField_(
                    stored_data['last-modified'], 'if-modified-since')
            if 'etag' in stored_data:
                request.setValue_forHTTPHeaderField_(
                    stored_data['etag'], 'if-none-match')
        self.connection = NSURLConnection.alloc().initWithRequest_delegate_(
            request, self)

z01_example_usage.py

from purl import Purl
from urllib import urlencode

form_data = [
             ("field1", "value1"),
             ("field2", "A complex value example:?!$"),
            ]

options = dict()
options["url"] = "http://localhost:8000/"
options["file"] = "/Users/mike/Desktop/out.data"
options["content_type"] = "application/x-www-form-urlencoded"
options["body"] = urlencode(form_data)
# Build Purl with initial settings
p = Purl.alloc().initWithOptions_(options)
# Start it
p.start()
# Need to collect the results to have it actually run
result = p.isDone()

z02_example_log.txt

WARNING:root:======= POST STARTED =======
WARNING:root:Host: localhost:8000
Content-Type: application/x-www-form-urlencoded
Connection: keep-alive
Accept: */*
User-Agent: Python/2.7.5 CFNetwork/673.5 Darwin/13.4.0 (x86_64) (MacBookAir6%2C2)
Accept-Language: en-us
Accept-Encoding: gzip, deflate
Content-Length: 56

WARNING:root:======= POST VALUES =======
WARNING:root:MiniFieldStorage('field1', 'value1')
WARNING:root:MiniFieldStorage('field2', 'A complex value example:?!$')
WARNING:root:

127.0.0.1 - - [08/Jun/2015 01:52:41] "POST / HTTP/1.1" 200 -