Is it a good idea to start learning Python? I'm a PHP dev but I really want to get out of my comfort zone and try something new. Moreover, I think as a PHP dev, I don't really have a future.

Made the same leap last year, php->python is definetly doable, there's different syntactic sugar (tabs vs braces, list comprehension) but you'll surely work through them after a tutorial or two. Build a project, cross that bridge.

In the words of Gandalf the Grey: Fly, you fool!

Yes it is a good idea to learn more languages (and python is a good language to learn).

You will probably always find work as a php dev though, the fact that the language is crap by todays standards is irrelevant when there are billions of lines of legacy code written in it and it is still being used for new development (Although it has been losing popularity the last few years).

Cobol is still alive and kicking, languages don't die that easily even when they deserve to.

I took the leap 3 years ago, I have no regrets!

Quick advice : stop being a PHP dev and become a dev :)
The language has little to do with programming, the paradigms are what's important