Thank you for your response smith. I took another look into what is wrong in the code and I find out that it is actually the response of add_to_cart function in the content field. The "content" field of the response of http post request is empty. A normal GET request will get a response like this:
cookies: <RequestsCookieJar[<Cookie __cfduid=d593c78ef47f421dac3c8c4e96547f45a1478526637 for .shapeways.com/>, <Cookie whid=12 for api.shapeways.com/>]>, _content:{"result":"success","modelId":"5221039","modelVersion":"0","title":"HBlogo","fileName":"HBlogo.stl","contentLength":1,"fileMd5Checksum":"c4ca4238a0b923820dcc509a6f75849b","fileData":"MQ==","nextActionSuggestions": some suggestions}, url:
https://api.shapeways.com/models/5221039/files/0/v1?file=1, status_code: 200, _content_consumed: True, encoding: utf-8, request: <PreparedRequest [GET]>, connection: <requests.adapters.HTTPAdapter object at 0x109c51310>, elapsed: 0:00:00.668650, raw: <requests.packages.urllib3.response.HTTPResponse object at 0x109d66210>, reason: OK, history: []
And the POST request for add_to_cart will get a response like this:
cookies: <RequestsCookieJar[<Cookie __cfduid=d72adcb1505edf4261dc4888a12a88c031478526693 for .shapeways.com/>, <Cookie whid=9 for api.shapeways.com/>]>,
_content: , headers: {'Content-Length': '0', 'Set-Cookie': '__cfduid=d72adcb1505edf4261dc4888a12a88c031478526693; expires=Tue, 07-Nov-17 13:51:33 GMT; path=/; domain=.shapeways.com; HttpOnly, whid=9; path=/', 'Accept-Ranges': 'none', 'Server': 'cloudflare-nginx', 'Connection': 'keep-alive', 'Date': 'Mon, 07 Nov 2016 13:51:33 GMT', 'CF-RAY': '2fe142bbd9d421fe-EWR', 'Content-Type': 'text/html; charset=UTF-8', 'Cf-Railgun': 'direct (waiting for pending WAN connection)'}, url:
https://api.shapeways.com/orders/cart/v1, status_code: 200, _content_consumed: True, encoding: UTF-8, request: <PreparedRequest [POST]>, connection: <requests.adapters.HTTPAdapter object at 0x1043d3f10>, elapsed: 0:00:00.290374, raw: <requests.packages.urllib3.response.HTTPResponse object at 0x1043da250>, reason: OK, history: []
You can see that the content field is empty for some reason. Is it something wrong with my python application code or is it something wrong with the API?
Thank you again for your response. And Sorry I did not make it clear the first time I made my post