TypeError：POST data should be bytes, an iterable of bytes, or a file object. It cannot be of str

Python2转Python3，调用API在线服务遇到的问题解决（json数据）

Python2代码示例：

import json
import traceback
import urllib
import urllib2

# json格式数据
formdata = {
    "CRIM":0.01887747, 
    "ZN":-0.11363636, 
    "INDUS":0.25525005, 
    "CHAS":-0.06916996
}
header = {"Content-Type": "application/json; charset=utf-8"}
url = "https://aistudio.baidu.com/serving/online/xxx?apiKey=a280cf48-6d0c-4baf-bd39xxxxxxcxxxxx"
data = json.dumps(formdata)
try:
    request = urllib2.Request(url, data, header)
    response = urllib2.urlopen(request)
    response_str = response.read()
    response.close()
    print(response_str)
except urllib2.HTTPError as e:
    print("The server couldn't fulfill the request")
    print(e.code)
    print(e.read())
except urllib2.URLError as e:
    print("Failed to reach the server")
    print(e.reason)
except:
    traceback.print_exc()

修改到Python3的代码

import json
import traceback
import urllib
# 1.首先去掉urllib2, python3统一使用urllib
# import urllib2

# json数据
formdata = {
    "CRIM":0.01887747, 
    "ZN":-0.11363636, 
    "INDUS":0.25525005, 
    "CHAS":-0.06916996
}
header = {"Content-Type": "application/json; charset=utf-8"}
url = "https://aistudio.baidu.com/serving/online/xxx?apiKey=a280cf48-6d0c-4baf-bd39xxxxxxcxxxxx"
data = json.dumps(formdata)

# 2.urllib2到urllib转换的语句修改
try:
    request = urllib.request.Request(url, data, header)
    # 输出字符串
    response = urllib.request.urlopen(request)
    response_str = response.read()
    response.close()
    print(response_str)
except urllib.error.HTTPError as e:
    print("The server couldn't fulfill the request")
    print(e.code)
    print(e.read())
except urllib.error.URLError as e:
    print("Failed to reach the server")
    print(e.reason)
except:
    traceback.print_exc()

但，运行之后会报如下错误：

TypeError: POST data should be bytes, an iterable of bytes, or a file object. It cannot be of type str.

查询到有些回答提到，必须使用urllib.parse.urlencode（）函数将请求转换为字节，再因此如下：

data = urllib.parse.urlencode(data).encode("utf-8")
# 此时再进行url请求
request = urllib.request.Request(url, data, header)

但这对json数据格式无效，发生新的错误：

TypeError: not a valid non-string sequence or mapping object

原因：json.dumps（data）只是将数组/字典转换为字符串，urllib.parse.urlencode函数无效，当要转换作为url参数传递的字符串（即：将空格字符转换为“％20”）时，使用urlencode ，此方法的输出是字符串，而不是字节数组。

正确解决方案

json.dumps()返回一个字符串，因此必须调用json.dumps().encode()将其转换为字节数组。

# data = urllib.parse.urlencode(data).encode("utf-8")
data = json.dumps(formdata).encode()

此时运行，问题解决。

b'[{"predict":[16.302953720092773]}]'