have tried to put some efforts to help you understand what affects technology to select

1. Demand Flexibility
Whenever a demands comes up, a lot of client restrictions follows like: they want the new website to be hosted on the same server, they do not want a new module to be installed, etc.
Let's see an example: Client X want's a new website and shares the basic requirement with restriction that they wan't to host this website on same server(linux).
As a consultant, we know that since the client has linux server, we cannot go for asp .net technology so we are restricted to technologies based on linux server same goes for others.


2. Billing Flexibility
When client is not flexible with billing or has fixed the maximum amount he will invest to his website. In this case, if the amount required to get license for relevant technology (Microsoft visual Studio for .net) may not be feasible.


3. Complexity of Website
If the site structure is complex and demands flexibility in terms of extension, you may not go for php alone, you might have to integrate several technologies together like php and python. You may also need help of some existing frameworks.


4. Deadline
Finally, this is the most important point. You cannot test new things including new technologies if you have strict deadline. Go for whatever technology the team is comfortable with.


Note:-
If time, bill and demand is not an issue you can go for any technology you want.
Suggestion(Just a suggestion, go for it if you wan't)
If demand is quit simple, go for php. It is extremely simple and flexible language.
If demand is dealing with heavy manipulation of words/strings/sentences go for perl/python. You may opt java as well, but surely not php.
If demand request complex design, go for python, java, C#/asp .net. And python has many frameworks flask and django are preety easy to get by

If demand needs extensibility at a later stage, i guess python integrated with other languages will be good for that.