kwargs sent over pyAMF channel

Question

Hello,

I'm using cherrypy server to receive requests over a pyAMF channel from a python client. I started with the mock up below and it works fine:

Server:

import cherrypy
from pyamf.remoting.gateway.wsgi import WSGIGateway

def echo(*args, **kwargs):
    return (args, kwargs)

class Root(object):
    def index(self):
        return "running"
    index.exposed = True

services = {
   'myService.echo': echo,
}

gateway = WSGIGateway(services, debug=True)

cherrypy.tree.graft(gateway, "/gateway/")
cherrypy.quickstart(Root())

Client:

from pyamf.remoting.client import RemotingService

path = 'http://localhost:8080/gateway/'
gw = RemotingService(path)
service = gw.getService('myService')

print service.echo('one=1, two=3')

Result: [[u'one=1, two=3'], {}]

now if instead of:

def echo(*args, **kwargs):
    return (args, kwargs)

I use:

def echo(**kwargs):
    return kwargs

and send the same request, I get the following error:

TypeError: echo() takes exactly 0 arguments (1 given)

while at the same time:

>>> def f(**kwargs): return kwargs
... 
>>> f(one=1, two=3)
{'two': 3, 'one': 1}
>>> 

Question: Why is this happening? Please share insights

I'm using: python 2.5.2, cherrypy 3.1.2, pyamf 0.5.1

Answer 1

Notice that with your first echo function, the only way to get the results you do is when it is called this way:

echo(u"one=1, two=3")
# in words: one unicode string literal, as a positional arg

# *very* different from:
echo(one=1, two=3) # which seems to be what you expect

Because of this, you must write echo to accept positional arguments or change how it is called.

Answer 2

By default, WSGIGateway sets expose_request=True which means that the WSGI environ dict is set as the first argument to any service method in that gateway.

This means that echo should be written as:

def echo(environ, *args):
    return args

PyAMF provides a decorator which allows you to forcibly expose the request even if expose_request=False, an example:

from pyamf.remoting.gateway import expose_request
from pyamf.remoting.gateway.wsgi import WSGIGateway

@expose_request
def some_service_method(request, *args):
    return ['some', 'thing']

services = {
    'a_service_method': some_service_method
}

gw = WSGIGateway(services, expose_request=False)

Hope that clarifies why you are getting the TypeError in this case.

You correctly point out that you cannot supply **kwargs directly in a PyAMF client/server call but you can use default named parameters:

def update(obj, force=False):
    pass

Then you can access the service:

from pyamf.remoting.client import RemotingService

path = 'http://localhost:8080/gateway/'
gw = RemotingService(path)
service = gw.getService('myService')

print service.update('foo', True)