Django is the best web framework in existence, bar none. It has loads of moving parts and is a total bitch to properly tune, but it is capable of high concurrency due to the nature of Python's ability to pre-compile and cache opcodes natively. PHP is definitely worth knowing for its popularity and high functionality, but Python and Java are still the king for high concurrency back end work.
If you want to have marketability, go with PHP. If you want to be a systems engineering god, go with Python, Java, and Django as the framework/CME.
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He is hold back the legion of boom - skater18000