We need to specify a directory to the Flask app where the uploaded files would be stored. Above line creates a uploads folder in the same directory where the src code of the site is stored. We should also check for file extension that the user is uploading as there would be some specific type of file that the site can process. Also there is security issue if the user can upload any type of file. User might upload html file that can cause XSS cross site-scripting problems.
For this post, we only need pdf file extensions as this Flask app would remove watermark from pdf files created by CamScanner App Famous App for scanning documents through Mobile Camera. Pdf files would have watermark at the bottom similar to what is shown in the image below :. We can also configure the directory for saving the file by configuring the app. At first, the uploaded file is saved into a temporary location, and then it moves to the final location.
The following code shows how to configure the upload directory. In the above code, we use the OS module of python to create a directory and saves every uploaded file to the created directory. If we restart the server and upload a file to the server, the file will be uploaded to the created directory instead of the root directory. We can also configure the maximum upload size of the file. This is important because if the file is too large for the server, then the site may crash.
So, we need to always limit the upload size of the file according to our server. To configure the maximum file size, we need to set the app. For example, if we want to limit the maximum size of the file to 1 Mb, we need to add the following line of code in our program.
After setting the maximum file size of the file in our python program, if we upload a file having a size of more than 1 Mb, then we will get the error as shown in the below image. While building a file uploader using Flask, we can also configure the file extensions that we want to upload. To configure the allowed file extensions, we need to create a list of allowed extensions and check the uploaded file extension in the list. The below code shows a practical illustration of the method.
In the above code, we create a function that will check the uploaded file extension and compare it with the allowed extensions. Till now, we have seen how to upload a single file to our server. But sometimes, we also want to upload multiple files to the server. See the below code for illustration. After creating the Html form, we need to make some changes to our Flask application file.
First, copy the following Python code into your Flask app file. In the above code, we use python for loop to iterate over the list of files and then save each file one by one. We can choose multiple files now and upload them at once to the server. We have seen how to upload files using Flask, but sometimes we also want to serve a file to the user.
First, create an HTML template in the templates folder, named the file download. Now, we need to create our app. In our app. Then, copy and paste the following code in the app. Podcast Who is building clouds for the independent developer? Exploding turkeys and how not to thaw your frozen bird: Top turkey questions Featured on Meta. Now live: A fully responsive profile. Reducing the weight of our footer. Linked 0. Related Hot Network Questions. Question feed. Stack Overflow works best with JavaScript enabled.
You could of course omit it and ask the user to provide the file extension too. You may want a nested directory structure within your trusted base directory, where users can provide a path to a file in the URL to retrieve a file. Let's say reports is our trusted base directory, containing several sub-directories and files, like so:. Without using a database, we can create a dynamic system of URL's and allow users to provide a path to a file.
Let's create a new route and put this into practice, allowing our user to download a report by providing a path in the URL. We're doing exactly the same as above, with the exception of adding the path prefix to the URL variable.
The path should be relative from the reports directory saved in our app. Likewise any non-existent filenames would throw a error. The reason? I'm sure you wouldn't want users to be able to downlaod any file from your application at their own will.
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