Button.click gets an empty file input

[RussellLuo]

Describe the bug

If I use a gr.File object as an input of Button.click(), the corresponding event handler function will get an empty file.

Is there an existing issue for this?

• I have searched the existing issues

Reproduction

import gradio as gr

with gr.Blocks() as demo:
    file = gr.File()
    upload = gr.Button('Upload')
    data = gr.Textbox(label='Data')
    upload.click(lambda f: f.read(), inputs=[file], outputs=[data])

demo.launch()

Screenshot

Logs

No helpful logs.

System Info

gradio==v3.23.1b2
Mac

Severity

blocking upgrade to latest gradio version

[abidlabs]

Hi @RussellLuo, the issue is that you are trying to call .read() on a temporary file wrapper (tempfile._TemporaryFileWrapper) and that is not supported. Try this instead:

import gradio as gr

def read(x):
    with open(x.name) as fo:
        return fo.read()

with gr.Blocks() as demo:
    file = gr.File()
    upload = gr.Button('Upload')
    data = gr.Textbox(label='Data')
    upload.click(read, inputs=[file], outputs=[data])

demo.launch()

I think the confusion may lie in the fact that the documentation for the File component is actually incorrect. It should state that the preprocessing method for gr.File should convert the uploaded file to a temporary file (`_TemporaryFileWrapper), not a file-object. For backwards compatibility, we won't change the behavior of File preprocessing, but if you'd like to adapt your PR to change the documentation, that would be welcome