Got strange response

[ipconfiger]

i use this file in a flask app.

code like below:

@app.route("/oauth/fitbit")
def test():
    from fitbit import FitBit
    c=FitBit()
    if "oauth_token" not in request.args:
        url,oauth_token = c.GetRequestToken()
        return redirect(url)
    auth_token = request.args.get("oauth_token")
    pin = request.args.get("oauth_verifier")
    access_token = c.GetAccessToken(pin, Row(key=auth_token,secret=pin,callback=None))
    return "%s"%c.ApiCall(access_token,apiCall="/1/user/~/profile.json")

when get access_token it works ok,but when i access the api get_user_info,it return a xml header

<?xml version="1.0" encoding="UTF-8" ?>

not json object, what happening?