Website Links to Downloadable Files Don't Seem to Update
I don't know anything about Python, but in PHP, in some fopen modes, if a file is trying to be made with the same name as an existing file, it will cancel the operation.
I have a problem with links on my website. Please forgive me if this is asked somewhere else, but I have no idea how to search for this.
A little background on the current situation:
I've created a python program that randomly generates planets for a sci-fi game. Each created planet is placed in a text file to be viewed at a later time. The program asks the user how many planets he/she wants to create and makes that many text files. Then, after all the planets are created, the program zips all the files into a file 'worlds.zip'. A link is then provided to the user to download the zip file.
The problem:
The first time I run this everything works perfectly fine. When run a second time, however, and I click the link to download the zip file it gives me the exact same zip file as I got the first time. When I ftp in and download the zip file directly I get the correct zip file, despite the link still being bad.
Things I've tried:
When I refresh the page the link is still bad. When I delete all my browser history the link is still bad. I've tried a different browser and that didn't work. I've attempted to delete the file from the web server and that didn't solve the problem. Changing the html file providing the link worked once, but didn't work a second time. 
Simplified Question:
How can I get a link on my web page to update to the correct file?
I've spent all day trying to fix this. I don't mind looking up information or reading articles and links, but I don't know how to search for this, so even if you guys just give me links to other sites I'll be happy (although directly answering my question will always be appreciated :)).