使用 Flask 上传文件列表时 request.files 为空

Question

I need to upload multiple files to a flask endpoint in a list. But request.files is empty when I try to upload a list of files, even if the list contains only one element. Look at this minimal example:

from flask import Flask, request
app = Flask(__name__)


@app.route('/', methods=['POST'])
def hello_world():
    assert len(request.files) > 0
    return 'Hello, World'


data_1 = {
    'a': '42',
    'file:': open('blue.jpg', mode='rb'),
    'text': 'this is blue',
}
data_2 = {
    'a': '42',
    'gallery': [{
        'file:': open('blue.jpg', mode='rb'),
        'text': 'this is blue',
    }],
}
client = app.test_client()
res = client.post('/', data=data_1, content_type='multipart/form-data')
assert res.status_code == 200  # all fine here
res = client.post('/', data=data_2, content_type='multipart/form-data')
assert res.status_code == 200  # fails

The last assertions fails:

[2021-03-03 15:29:46,597] ERROR in app: Exception on / [POST]
Traceback (most recent call last):
  File "/home/wsontopski/PycharmProjects/pythonProject1/venv/lib/python3.8/site-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/wsontopski/PycharmProjects/pythonProject1/venv/lib/python3.8/site-packages/flask/app.py", line 1952, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/wsontopski/PycharmProjects/pythonProject1/venv/lib/python3.8/site-packages/flask/app.py", line 1821, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/wsontopski/PycharmProjects/pythonProject1/venv/lib/python3.8/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/home/wsontopski/PycharmProjects/pythonProject1/venv/lib/python3.8/site-packages/flask/app.py", line 1950, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/wsontopski/PycharmProjects/pythonProject1/venv/lib/python3.8/site-packages/flask/app.py", line 1936, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/wsontopski/PycharmProjects/pythonProject1/main.py", line 7, in hello_world
    assert len(request.files) > 0
AssertionError
Traceback (most recent call last):
  File "/home/wsontopski/PycharmProjects/pythonProject1/main.py", line 27, in <module>
    assert res.status_code == 200
AssertionError

Do you have any idea how I can fix this?

Answer 1

The problem with second request is that you are trying to send an array of files along with some data which is not possible. If you see the request structure for request.post() method it looks something like this:

{
    "args": {},
    "data": "",
    "files": {},
    "form": {
       
    },
    "headers": {
    },
    "json": null,
    "origin": "",
    "url": ""
}

So you will have to send all the files outside the array (in files param) while your text should go in "form" param. For sending multiple files you can do something like this:

>>> url = 'https://httpbin.org/post'
>>> multiple_files = [
...     ('images', ('foo.png', open('foo.png', 'rb'), 'image/png')),
...     ('images', ('bar.png', open('bar.png', 'rb'), 'image/png'))]
>>> r = requests.post(url, files=multiple_files)

Source: https://requests.readthedocs.io/en/master/user/advanced/#post-multiple-multipart-encoded-files

Edit 1: For test client, you will have to create your data object like below:

data_1 = {
    'a': '42',
    'blue:': open('blue.jpg', mode='rb'),
    'red:': open('red.jpg', mode='rb'),
    'text': 'this is blue',
}

Answer 2

I solved the problem: Using MultiDict solves the problem:

data_1 = {
    'a': '42',
    'file': open('blue.jpg', mode='rb'),
    'file2': open('blue.jpg', mode='rb'),
    'text': 'this is blue',
}
data_2 = MultiDict([
    ('a', '42'),
    ('file', open('blue.jpg', mode='rb')),
    ('file', open('blue.jpg', mode='rb')),
    ('text', 'this is blue'),
])

client = app.test_client()
res = client.post('/', data=data_1, content_type='multipart/form-data')
assert res.status_code == 200

res = client.post('/', data=data_2, content_type='multipart/form-data')
assert res.status_code == 200

Output:

[]
[<FileStorage: 'blue.jpg' ('image/jpeg')>, <FileStorage: 'blue.jpg' ('image/jpeg')>]