params.py

import functools                                                                                                       
                                                                                                                       
                                                                                                                       
def common(accepts):                                                                                                   
    def wrap(f):                                                                                                       
        f.__doc__ += """                                                                                               
        *token* i take a token                                                                                         
"""                                                                                                                    
        d = {}                                                                                                         
        exec("""                                                                                                       
def __(self, token=None):                                                                                              
    params = {}                                                                                                        
    if token:                                                                                                          
        params["token"] = token                                                                                        
    else:                                                                                                              
        params["token"] = self.agent                                                                                   
    f(self, params)                                                                                                    
""", {'f': f}, d)                                                                                                      
        functools.update_wrapper(d['__'], f)                                                                           
        return d['__']                                                                                                 
    return wrap                                                                                                        
                                                                                                                       
                                                                                                                       
class C(object):                                                                                                       
    agent = "agent default"                                                                                            
                                                                                                                       
    @common(["token"])
    def bar(self, params):                                                                                             
        """                                                                                                            
        My docstring!                                                                                                  
        """                                                                                                            
        print params                                                                                                   
                                                                                                                       
                                                                                                                       
c = C()                                                                                                                
                                                                                                                       
print c.bar                                                                                                            
print c.bar.__doc__                                                                                                    
c.bar()                                                                                                                
c.bar(token="hi") 

$ python ~/tmp/params.py 
<bound method C.bar of <__main__.C object at 0x103d92850>>

        My docstring!

        *token* i take a token

{'token': 'agent default'}
{'token': 'hi'}