python requests post query fails:cookies?

Most API access points on that site appear to be broken. There is nothing wrong with your code per-se. I can't actually get the site to respond to any requests in their own webinterface, even when using a regular browser.

The main API documentation details (in French) that you can also use the SOAP protocol to create queries; Python has several SOAP client libraries you could choose from.

However, I've had no luck in getting that to work either. Using the excellent zeep library I tried to access the simpler GetMainCarMakeListByFirstDrivingDate endpoint (note that I had to use a datetime() object to model the timestamp):

>>> from zeep import Client
>>> client = Client('https://www.assurland.com/ws/CarVehiculeSearch.asmx?WSDL')
>>> client.service.GetMainCarMakeListByFirstDrivingDate(FirstDrivingDate=datetime(2015, 9, 22))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mjpieters/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/zeep/client.py", line 25, in __call__
    self._op_name, args, kwargs)
  File "/Users/mjpieters/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/zeep/wsdl/bindings/soap.py", line 109, in send
    return self.process_reply(client, operation_obj, response)
  File "/Users/mjpieters/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/zeep/wsdl/bindings/soap.py", line 145, in process_reply
    return self.process_error(doc, operation)
  File "/Users/mjpieters/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/zeep/wsdl/bindings/soap.py", line 223, in process_error
    detail=fault_node.find('detail'))
zeep.exceptions.Fault: <exception str() failed>

a Fault is the SOAP equivalent of a 500 error here.

When I enable debug logging, we can see that the server is having problems producing a response:

>>> client.service.GetMainCarMakeListByFirstDrivingDate(FirstDrivingDate=datetime(2015, 9, 22))
zeep.transports: HTTP Post to https://www.assurland.com/ws/CarVehiculeSearch.asmx:
<?xml version='1.0' encoding='utf-8'?>
<soap-env:Envelope xmlns:soap-env="http://schemas.xmlsoap.org/soap/envelope/">
  <soap-env:Body>
    <ns0:GetMainCarMakeListByFirstDrivingDate xmlns:ns0="http://tempuri.org/">
      <ns0:FirstDrivingDate>2015-09-22T00:00:00</ns0:FirstDrivingDate>
    </ns0:GetMainCarMakeListByFirstDrivingDate>
  </soap-env:Body>
</soap-env:Envelope>

zeep.transports: HTTP Response from https://www.assurland.com/ws/CarVehiculeSearch.asmx (status: 500):
<?xml version="1.0" encoding="utf-8"?><soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><soap:Body><soap:Fault><faultcode>soap:Server</faultcode><faultstring>Le serveur n'a pas pu traiter la demande. ---&gt; Erreur lors de la génération du document XML. ---&gt; Le type common.FormDataListItem n'était pas attendu. Utilisez l'attribut XmlInclude ou SoapInclude pour spécifier les types qui ne sont pas connus statiquement.</faultstring><detail /></soap:Fault></soap:Body></soap:Envelope>
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mjpieters/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/zeep/client.py", line 25, in __call__
    self._op_name, args, kwargs)
  File "/Users/mjpieters/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/zeep/wsdl/bindings/soap.py", line 109, in send
    return self.process_reply(client, operation_obj, response)
  File "/Users/mjpieters/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/zeep/wsdl/bindings/soap.py", line 145, in process_reply
    return self.process_error(doc, operation)
  File "/Users/mjpieters/Development/venvs/stackoverflow-2.7/lib/python2.7/site-packages/zeep/wsdl/bindings/soap.py", line 223, in process_error
    detail=fault_node.find('detail'))
zeep.exceptions.Fault: <exception str() failed>

Hidden in there is the error message:

Le serveur n'a pas pu traiter la demande. ---> Erreur lors de la génération du document XML. ---> Le type common.FormDataListItem n'était pas attendu. Utilisez l'attribut XmlInclude ou SoapInclude pour spécifier les types qui ne sont pas connus statiquement.

or, with some Google Translate help, in English:

The server could not process the request. ---> Error generating the XML document. ---> The type common.FormDataListItem was not expected. Use XmlInclude or SoapInclude attribute to specify types that are not known statically.

Since we are not sending any common.FormDataListItem types, and the message complains that no XML document could be generated, this looks like a server-side programming error to me.

There are methods that do work, either via SOAP:

>>> client.service.GetCarTypeListByCodeMake(CodeMake='BMW', FirstDrivingDate=datetime(2016, 1, 1))
['I3', 'I8', 'M2', 'M3', 'M4', 'M5', 'M6', 'SERIE 1 II', 'SERIE 2', 'SERIE 3 VI', 'SERIE 4', 'SERIE 5', 'SERIE 6', 'SERIE 7', 'X1', 'X3', 'X4', 'X5', 'X6', 'Z4']
>>> client.service.GetAllCarTypeListByCodeMake(CodeMake='BMW')
['1502', '1600', '1602', '1800', '1802', '2000', '2002', '2500', '3,0', '3,3', '315', '316', '318', '320', '323', '324', '325', '328', '330', '518', '520', '523', '524', '525', '528', '530', '535', '540', '545', '550', '628', '630', '633', '635', '645', '650', '725', '728', '730', '732', '733', '735', '740', '745', '750', '760', '840', '850', 'I3', 'I8', 'L7', 'M2', 'M3', 'M4', 'M5', 'M535', 'M6', 'M635', 'SERIE 1', 'SERIE 1 II', 'SERIE 2', 'SERIE 3', 'SERIE 3 (SUITE)', 'SERIE 3 VI', 'SERIE 4', 'SERIE 5', 'SERIE 6', 'SERIE 7', 'X1', 'X3', 'X4', 'X5', 'X6', 'Z1', 'Z3', 'Z4', 'Z8']

or via posting application/x-www-form-urlencoded data with requests:

>>> response = requests.post('https://www.assurland.com/ws/CarVehiculeSearch.asmx/GetCarTypeListByCodeMake', data={'CodeMake': 'BMW', 'FirstDrivingDate': datetime(2016, 1, 1)})
>>> print(response.text)
<?xml version="1.0" encoding="utf-8"?>
<ArrayOfAnyType xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://tempuri.org/">
  <anyType xsi:type="xsd:string">I3</anyType>
  <anyType xsi:type="xsd:string">I8</anyType>
  <anyType xsi:type="xsd:string">M2</anyType>
  <anyType xsi:type="xsd:string">M3</anyType>
  <anyType xsi:type="xsd:string">M4</anyType>
  <anyType xsi:type="xsd:string">M5</anyType>
  <anyType xsi:type="xsd:string">M6</anyType>
  <anyType xsi:type="xsd:string">SERIE 1 II</anyType>
  <anyType xsi:type="xsd:string">SERIE 2</anyType>
  <anyType xsi:type="xsd:string">SERIE 3 VI</anyType>
  <anyType xsi:type="xsd:string">SERIE 4</anyType>
  <anyType xsi:type="xsd:string">SERIE 5</anyType>
  <anyType xsi:type="xsd:string">SERIE 6</anyType>
  <anyType xsi:type="xsd:string">SERIE 7</anyType>
  <anyType xsi:type="xsd:string">X1</anyType>
  <anyType xsi:type="xsd:string">X3</anyType>
  <anyType xsi:type="xsd:string">X4</anyType>
  <anyType xsi:type="xsd:string">X5</anyType>
  <anyType xsi:type="xsd:string">X6</anyType>
  <anyType xsi:type="xsd:string">Z4</anyType>
</ArrayOfAnyType>

You'll probably have to contact the maintainers of this API to get this sorted out, this is not something you can get to work on the Python side.