Download file using flask

We need to learn to upload and download files using server-side frameworks like Flask in such a scenario. We can install Flask easily with the help of the pip tool.

PIP is a command-line tool, and it is the default package manager for managing python packages. To install the Flask framework, we need to run the following command in the terminal. On running the above command in the terminal, we will have Flask installed in our system. We can check our installation by opening the python shell and importing the Flask library. See the below image for illustration. The first step while creating our file uploader is to build the Html form.

First, create a templates folder in the current directory. After that, create a file with the name upload. After creating the HTML template for the file uploader, now, in the main directory, create a file with the name app. The app. Copy the following code into the app. In the above code, we first imported the required modules to our code. After importing the required modules, we initialize the Flask app by calling the Flask constructor.

Next, we use python decorators to define the routes for our Flask app and serve the HTML template that we created. Next, we use python decorators to accept the post request for the file and save the file. You can run the above code by just typing python app. We will see something as shown in the below image while running the above code.

Upload a sample file by choosing a file and clicking the submit button. After submitting the file, we will get a message showing that the file has been successfully uploaded. We can check the file in the server by visiting the root directory.

The solution for these cases require variations of the upload view function shown above, with additional access checks. A common requirement is to only share uploaded files with their owner. A convenient way to store uploads when this requirement is present is to use a separate directory for each user. Below you can see a possible implementation of this technique, once again assuming Flask-Login is used:.

Up until now we have relied on the native file upload widget provided by the web browser to initiate our file uploads. I'm sure we can all agree that this widget is not very appealing.

Not only that, but the lack of an upload progress display makes it unusable for uploads of large files, as the user receives no feedback during the entire upload process. While the scope of this article is to cover the server side, I thought it would be useful to give you a few ideas on how to implement a modern JavaScript-based file upload widget that displays upload progress.

The good news is that on the server there aren't any big changes needed, the upload mechanism works in the same way regardless of what method you use in the browser to initiate the upload. That's basically it! You can now drop files and they'll be uploaded to the server with a progress bar and a final indication of success or failure.

If the file upload fails, either due to the file being too large or invalid, dropzone wants to display an error message. Because our server is currently returning the standard Flask error pages for the and errors, you will see some HTML gibberish in the error popup.

To correct this we can update the server to return its error responses as text. The error for the file too large condition is generated by Flask when the request payload is bigger than the size set in the configuration.

To override the default error page we have to use the app. The second error condition is generated by the application when any of the validation checks fails. In this case the error was generated with a abort call. Instead of that the response can be generated directly:. The final change that I'm going to make isn't really necessary, but it saves a bit of bandwidth.

For a successful upload the server returned a redirect back to the main route. This caused the upload form to be displayed again, and also to refresh the list of upload thumbnails at the bottom of the page. None of that is necessary now because the uploads are done as background requests by dropzone, so we can eliminate that redirect and switch to an empty response with a code The dropzone.

You can also look for other JavaScript file upload libraries, as they all follow the HTTP standard, which means that your Flask server is going to work well with all of them. This was a long overdue topic for me, I can't believe I have never written anything on file uploads! I'd love you hear what you think about this topic, and if you think there are aspects of this feature that I haven't covered in this article.

Feel free to let me know below in the comments! Hello, and thank you for visiting my blog! If you enjoyed this article, please consider supporting my work on this blog on Patreon! A couple of additional thoughts: It could be a good addition to introduce a check, whether the file already exists - before trying to save it not necessarily for the avatar use case, though Recently, I started answering Flask questions on StackOverFlow, and I noticed, that seemingly nobody writes tests nor knows how to use a debugger.

This may be related to the fact that both Python and Flask are very beginner friendly. But maybe it is also related that even the very high quality Flask tutorials hardly ever mention those techniques. What do you think about adding a box "Advanced Also, lots of these Flask questions on StackOverFlow are like "I followed this tutorial but it does not work for me".

Usually, this can be easily resolved with a debugger. While a five minute talk only can give a quick overview, maybe this could be an idea for a future blog post of yours? All the best, and maybe we see each other at the next "Python Ireland Monthly Meetup"?

Uploaded file attached in the POST request can be referenced by request. We check the name of the uploaded file before we save it to server filesystem. This is done because there is a possibility that user might name the file which clashes with some system configuration file, In this case if uploaded filename is not changed then system file will be overwritten.

This vulnerability can be used by hackers to hack the server. For this task i. First we should be able to read pdf file, for that we would use PyPDF2 module.

How do I force the download without a server? So just an html page with some javascript. Show 5 more comments. John Culviner John Culviner Your modern example here doesn't seem to me to make a great deal of sense. MarkAmery that works too as other answers have indicated. That approach AFAIK doesn't give you feedback on when the download starts, when it completed and if it errored which is handy.

I could add that to the answer for a "fire and forget" option. Also the [download] attribute doesn't allow for a POST or anything exotic either. Your modern example is not quite right. It will "download" whatever the server returns. For ex, if you have an authentication error, it will return the login page or whatever the server returns and not the "downloaded file" itself. Imagine Breaker Imagine Breaker 1, 1 1 gold badge 10 10 silver badges 8 8 bronze badges. For me this would be perfect but it doesn't not work on Firefox neither.

Any idea? As mentioned in caniuse. So if your links points to another domain, it hardly works anywhere for now. For it to work on Firefox, do document.

You can also do link. Show 3 more comments. Tomer 1, 13 13 silver badges 14 14 bronze badges. Chrome downloads, but Firefox just shows the picture. Saved me the time to test it only to find out it won't work.

Latest Chrome Aug shows picture too because of an absurd security restriction so fail — user Chrome doesn't download for mp4 s — Nearoo. Show 2 more comments. Mark Amery k 65 65 gold badges silver badges bronze badges. Laura Chesches Laura Chesches 2, 17 17 silver badges 15 15 bronze badges. Also the Edge 13 implementations is buggy because the name of the file is ignored and instead you get a file with an id as the name.

In my opinion, this is the correct answer to the question. The other answers make sense if you have to support older browsers and need a workaround. I dont' think is needed. It's already setting the 'src:url' in the creation step. I had to used "window. Maybe because I wanted to download 12 things at the same time?

Does not do anything in Chrome — jjxtra. This is base javascript function, so can be used in any platform where backend is in Javascript window. The file could be of any type of file, i. In this example there will be a simple UI user Interface , where a link will be provided to the end users and clicking on the download link a file will be download.

The downloaded file will ask you to choose a file location for saving it. There could be any reason to download a file from server. The reason could be, you want to generate reports from database and download these reports. Now I will create the web application that will download any kind of file which is kept in a server location.

First step is to create a project root directory under which I will put all the required files for the project.