How to encode string array as fieldin Python 3.7 using requests_toolbelt

In my request, I have an array with string values and numbers. Here is a simple example:

import requests
from requests_toolbelt.multipart.encoder import MultipartEncoder
m = MultipartEncoder(
    fields={'field0': 'value', 'field1': ['Test1', 'test2'],
            'field2': ('filename', 'test', 'text/plain')})
r = requests.post('http://httpbin.org/post', data=m, headers={'Content-Type': m.content_type})
print(r.text)

It woks but reqest is invalid. Here is response:

{
  "args": {}, 
  "data": "", 
  "files": {
    "field1": "test2", 
    "field2": "test"
  }, 
  "form": {
    "field0": "value"
  }, 
  "headers": {
    "Accept": "*/*", 
    "Accept-Encoding": "gzip, deflate", 
    "Content-Length": "378", 
    "Content-Type": "multipart/form-data; boundary=99e888bfc6254e4b8a428f9f234a7be0", 
    "Host": "httpbin.org", 
    "User-Agent": "python-requests/2.22.0", 
    "X-Bluecoat-Via": "85fb7b65b90c79fc"
  }, 
  "json": null, 
  "url": "https://httpbin.org/post"
}

I am unsing:

• requests_toolbelt v.0.9.1
• requests v.2.22.0

Here is an example of how to fix it.

import requests
from requests_toolbelt.multipart.encoder import MultipartEncoder
m = MultipartEncoder(
    fields=[
        ('field0', 'value'), ('field1', 'Test1'), ('field1', 'Test2'), 
        ('field2', ('filename', 'test', 'text/plain'))
        ] 
    )
r = requests.post('http://httpbin.org/post', data=m, headers={'Content-Type': m.content_type})
print(r.text)

Result:

{
  "args": {}, 
  "data": "", 
  "files": {
    "field2": "test"
  }, 
  "form": {
    "field0": "value", 
    "field1": [
      "Test1", 
      "Test2"
    ]
  }, 
  "headers": {
    "Accept": "*/*", 
    "Accept-Encoding": "gzip, deflate", 
    "Content-Length": "452", 
    "Content-Type": "multipart/form-data; boundary=3034efa776d04f4cb83f899783386e3a", 
    "Host": "httpbin.org", 
    "User-Agent": "python-requests/2.22.0", 
    "X-Bluecoat-Via": "9ca77bf6f5d34bc6"
  }, 
  "json": null, 
  "url": "https://httpbin.org/post"
}