Raising incorrect error when passing array to data

httpx Version: 0.28.1

import asyncio, httpx

async def test():
    sync_client = httpx.Client(base_url="https://httpbin.org")
    async_client = httpx.AsyncClient(base_url="https://httpbin.org")

    try:
        response = await async_client.request("POST", "/post", data=[{"a": "b"}])
        print(response)
    except Exception as e:
        print(e)

    try:    
        response = sync_client.request("POST", "/post", data=[{"a": "b"}])
        print(response)
    except Exception as e:
        print(e)


asyncio.run(test())

Attempted to send an sync request with an AsyncClient instance.
sequence item 1: expected a bytes-like object, dict found

In data, judging by the code sources, you can only pass strings, dictionaries, or bytes (+= arrays of bytes). If you pass any array other than a byte array to data, it will raise an incorrect error: Attempted to send a sync request with an AsyncClient instance. (We're using an asynchronous client to send an asynchronous request, mhm)
Honestly, I'm too lazy to look through the sources and figure out what went wrong, but in general, it should return the same error as it does with a synchronous client - sequence item 1: expected a bytes-like object, dict found.

Hi!
I have not been able to replicate this error, it currently returns “Use ‘content=<...>’ to upload raw bytes/text content.”

I just created a venv, installed httpx, and got the same exceptions as mentioned above. Also tried with python 3.12.8 but got same result

There is some data and traceback

Win11 24h2
(.venv) PS D:\Google Drive Files\Projects\!CurrentWork\httpx.test> pip freeze

anyio==4.8.0
certifi==2024.12.14
h11==0.14.0
httpcore==1.0.7
httpx==0.28.1
idna==3.10
sniffio==1.3.1
typing_extensions==4.12.2

(.venv) PS D:\Google Drive Files\Projects\!CurrentWork\httpx.test> python -V

Python 3.11.5

(.venv) PS D:\Google Drive Files\Projects\!CurrentWork\httpx.test> python .\test.py

Attempted to send an sync request with an AsyncClient instance.
sequence item 1: expected a bytes-like object, dict found

(.venv) PS D:\Google Drive Files\Projects\!CurrentWork\httpx.test> cat .\test.py

import asyncio, httpx

async def test():
    sync_client = httpx.Client(base_url="https://httpbin.org")
    async_client = httpx.AsyncClient(base_url="https://httpbin.org")

    try:
        response = await async_client.request("POST", "/post", data=[{"a": "b"}])
        print(response)
    except Exception as e:
        print(e)

    try:
        response = sync_client.request("POST", "/post", data=[{"a": "b"}])
        print(response)
    except Exception as e:
        print(e)


asyncio.run(test())

@AS7RIDENIED

In data, judging by the code sources, you can only pass strings, dictionaries, or bytes (+= arrays of bytes). If you pass any array other than a byte array to data, it will raise an incorrect error: Attempted to send a sync request with an AsyncClient instance. (We're using an asynchronous client to send an asynchronous request, mhm) Honestly, I'm too lazy to look through the sources and figure out what went wrong, but in general, it should return the same error as it does with a synchronous client - sequence item 1: expected a bytes-like object, dict found.

@AS7RIDENIED : I don't think you can pass in anything other than a dictionary with lists as values for form data. I tried this and it returned a 200:

response = await async_client.request("POST", "/post", data={'key1': ['value1', 'value2']})

with this data:

  "form": {
    "key1": [
      "value1", 
      "value2"
    ]
  },

Reference: https://www.python-httpx.org/compatibility/#query-parameters

@AS7RIDENIED : I don't think you can pass in anything other than a dictionary with lists as values for form data. I tried this and it returned a 200:

The essence of this issue is that the httpx returns an incorrect error when working with an asynchronous client. I know what can be passed and what cannot, thanks

Hey, I looked into this issue and the error

TypeError: sequence item 1: expected a bytes-like object, dict found

happens because data=[{"a": "b"}] gets passed all the way to h11 when using Client.
With AsyncClient, the same input fails earlier in _send_single_request, but the error message is misleading — it says it's a sync request issue, when the real problem is the invalid data format.

The root cause is that _content.encode_request() doesn't validate data properly. A fix would be to add type checks there to catch invalid formats like lists of dicts early on.

I was able to work around this by using json=data instead of data=data`

Fix confusing error message for invalid data parameter

Navigation Menu

Repository navigation

Raising incorrect error when passing array to data #3471

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Raising incorrect error when passing array to data #3471

Description

Activity

bagowix commented on Jan 22, 2025

AS7RIDENIED commented on Jan 23, 2025

jfleach commented on Mar 13, 2025

AS7RIDENIED commented on Mar 20, 2025

sreeharin commented on May 30, 2025

tiny-pangolin commented on Jan 1, 2026

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions