


How to Upload File using FastAPI?
Problem:
When attempting to upload a file using FastAPI according to the official documentation, the file2store variable is consistently empty. Rare instances of successful file byte retrieval occur, but this is uncommon.
Solution:
1. Install Python-Multipart:
To enable file uploading, which is transmitted as "form data," install python-multipart if you haven't already:
pip install python-multipart
2. Use .file Attribute for Single File Upload:
Use the .file attribute of the UploadFile object to obtain the actual Python file (i.e., SpooledTemporaryFile). This allows you to call methods like .read() and .close().
Example:
from fastapi import File, UploadFile @app.post("/upload") def upload(file: UploadFile = File(...)): try: contents = file.file.read() with open(file.filename, 'wb') as f: f.write(contents) except Exception: return {"message": "Error uploading file."} finally: file.file.close() return {"message": f"Successfully uploaded {file.filename}"}
3. Handle Large Files:
Use chunks if the file exceeds the 1MB memory limit. Adjust the chunk size as needed.
4. Asynchronous Reading/Writing:
If your endpoint requires async def, use asynchronous methods for reading and writing the file contents.
5. Upload Multiple Files:
@app.post("/upload") def upload(files: List[UploadFile] = File(...)): for file in files: try: contents = file.file.read() with open(file.filename, 'wb') as f: f.write(contents) except Exception: return {"message": "Error uploading file(s)."} finally: file.file.close() return {"message": f"Successfully uploaded {[file.filename for file in files]}."}
6. HTML Form Example:
Refer to the provided link for an example HTML form to upload files.
The above is the detailed content of Why is my FastAPI file upload always empty, and how can I fix it?. For more information, please follow other related articles on the PHP Chinese website!

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