Multipart doesn't support tuple data value

[andreymal]

This works:

client.post(
    url,
    data={"foo": ("1", "2")},  # tuple
)

This works:

client.post(
    url,
    data={"foo": ["1", "2"]},  # list
    files={"test": b"test"},
)

This fails:

client.post(
    url,
    data={"foo": ("1", "2")},  # tuple
    files={"test": b"test"},
)

Traceback

  File "httpx/_client.py", line 356, in build_request
    return Request(
  File "httpx/_models.py", line 336, in __init__
    headers, stream = encode_request(content, data, files, json)
  File "httpx/_content.py", line 210, in encode_request
    return encode_multipart_data(data or {}, files, boundary)
  File "httpx/_content.py", line 155, in encode_multipart_data
    multipart = MultipartStream(data=data, files=files, boundary=boundary)
  File "httpx/_multipart.py", line 188, in __init__
    self.fields = list(self._iter_fields(data, files))
  File "httpx/_multipart.py", line 198, in _iter_fields
    yield DataField(name=name, value=value)
  File "httpx/_multipart.py", line 36, in __init__
    raise TypeError(
TypeError: Invalid type for value. Expected primitive type, got <class 'tuple'>: ('1', '2')

I guess this line:

https://github.com/encode/httpx/blob/93de1980fa77f15c6b23cbaf2422c0a812caf243/httpx/_multipart.py#L194

should be implemented in the same way as this line:

https://github.com/encode/httpx/blob/93de1980fa77f15c6b23cbaf2422c0a812caf243/httpx/_content.py#L141