It's a better language. Better performance, better typing, better syntax, and so on.
Build an application in Python, then as soon as it becomes pushed by load you're going to need a rewrite. A few small load balancers and virtual web servers doing PHP can handle tens of thousands of requests per second, the database is almost guaranteed to be the bottleneck.
Python is a (according to some) nicer bash, it's not a good alternative for implementing non-trivial systems and web services.
Build an application in Python, then as soon as it becomes pushed by load you're going to need a rewrite. A few small load balancers and virtual web servers doing PHP can handle tens of thousands of requests per second, the database is almost guaranteed to be the bottleneck.
Python is a (according to some) nicer bash, it's not a good alternative for implementing non-trivial systems and web services.