如何通过 Flask 中的 API 检查来自 POST 请求的数据类型？ 如果传入的数据不是图像，则引发错误

Question

I have a portion of code like this:

@app.route('/', methods=['POST'])
def predict():
  
   if flask.request.method == 'POST':
           #global mymodel
           first  =datetime.now()
           f = request.files["img"].read()
           f = Image.open(io.BytesIO(f))

This code predicts whether an image is Spam or not. I want to RaiseCustomError with a messsage Please upload an image But for this I need to detect the data type of the incoming ByteString . I have thought about using the f = Image.open(io.BytesIO(f)) inside a try block so when an error occurs, it can perform

exception as e:
    return e

but that is stupid to do in my own opinion.

How can I detect the type of data from POST request so that if it not something belonging to any of Image type, I can raise a custom error with a message.

`

Answer 1

Check the file extension whether they are in the allowed list. You can customize the list with the image type that you wanna allow. For example,

def allowed_file(filename):
    return '.' in filename and filename.rsplit('.', 1)[1].lower() in ["png", "jpg"]

Before reading the image you can check the extension like this way

given_file = request.files["img"]
if given_file and allowed_file(given_file.filename):
    # Write your code here
else:
    abort(400, 'File is not a valid image type')