This should not happen. The user should receive a message that they are trying to upload an invalid file (I suppose that this is the reason why it crashes, I haven't investigated the issue further, just noticed it). The application should not just crash, especially not with an unhelpful error message like this.
When the user tries to upload an invalid input file, e.g. the readme.md from the repository, the application crashes with "UnboundLocalError: local variable 'df_temp' referenced before assignment" on this line: https://github.com/DEpt-metagenom/MetagenoMongo/blob/235ccc765a0cabaa7d4ae355b2074b691ce16026/flask-version/metagenomongo/app.py#L140
This should not happen. The user should receive a message that they are trying to upload an invalid file (I suppose that this is the reason why it crashes, I haven't investigated the issue further, just noticed it). The application should not just crash, especially not with an unhelpful error message like this.