I don't want to start a PHP vs language x discussion. My question is: given that I would, all else being equal, prefer to learn python+django rather than PHP, would this make it difficult to ever get a job as a web developer? Do professional web developers generally need to know PHP, even if they know other languages that can do the same things?
Both can be used to create great things. The difference is what you want to create. It depends on the employers want and needs. I would say, in the end learn both, but first, choose which ever one you feel the most comfortable with. If you want to start with python start with python, but in the end, you should learn php.
I would say its best to know even just basic PHP as im employed as a front end HTML developer but over time i have had to build some PHP scripts because the seniors were all booked for weeks in advanced.
So do you think an employer would ever employ a django developer who didn't know PHP?
In my opinion, it depends on what they want done. But yes, I would suggest going with php as well.
Most companies and jobs have a single focus such as; Java, Python, Ruby, C family, PHP, etc. Therefore, employment as a python developer would not require knowledge of PHP. There would be some jobs that perhaps ask for both though, but that is the same with all opportunities here and there. Does it help to know more than a single language, of course, can you do well with a specific focus yes. If you dsire to wrk at a Python shop than Python is the way to go. That will limit your focus on jobs, but that can be good and bad depending on how you look at it.