InvalidParameterValue error returned when calling the Amazon MWS API

#-*-coding:utf-8-*-
from time import strftime, gmtime
from requests import request
import base64
import hashlib
import hmac
import urllib.parse

param = {
    'AWSAcessKeyId': 'xxxx',
    'Action': 'ListMatching Products',
    'SellerId': 'xxxx',
    'SignatureMethod': 'HmacSHA256',
    'SignatureVersion': '2',
    'Timestamp': strftime("%Y-%m-%dT%H:%M:%SZ", gmtime()) ,
    'Version': '2011-10-01',
    'Query': "harrypotter"
}

data="POST\nmws.amazonservices.jp\nProducts/2011-10-01\n/"
format_param="&".join(['{0}={1}.format(key, urllib.parse.quote(param[key], safe='-_.~').encode('utf-8'))) for key in sorted(param)])
before_sign_data="{0}{1}.format(data,format_param)
hmacstr=hmac.new(b"secretKey", bytes(before_sign_data.encode('UTF-8')), hashlib.sha256).digest()
base64str = base64.b64encode(hmacstr)

url="{0}{1}?{2}&Signature={3}".format("https://mws.amazonservices.jp", "/Products/2011-10-01", format_param, urlib.parse.quote(base64str))
headers={'User-Agent':'python-app-mws/0.0.1(Language=Python)'}
response=request("POST", url_param, data={}, headers=headers)
data=response.content

print(data)

b'<?xml version="1.0"?>\n;ErrorResponse xmlns="https://mws.amazonservices.com/">\n  <Error>\n    <Type>Sender</Type>\n    <Code>InvalidParameterValue</Code>\n    <Message>Value b&apos;2&apos; for parameter SignatureVersion is invalid.</Message>\n  </Error>\n  <RequestID>6e29a554-c2d2-4b23-9f99-276aa250d239</RequestID>\n</ErrorResponse>\n'

https://mws.amazonservices.jp/Products/2011-10-01?AWSAccessKeyId=b'xxxxx'&Action=b'ListMatchingProducts'&Query=b'harry%20potter'&SellerId=b'xxxxx'&SignatureMethod=b'HmacSHA256'&SignatureVersion=b'2'&Timestamp=b'2017-03-07T15%3A22%3A32Z'&Version=b'2011-10-01'&Signature=v/lujNiPl8NZTkWmDQXRsAfhiX1GTLOOE7erK26QHDA%3D