Aside from everything already said, C integrates very well with Python; understanding C will let you write Python bindings for new libraries and will let you ea

Aside from everything already said, C integrates very well with Python; understanding C will let you write Python bindings for new libraries and will let you easily rewrite performance-critical chunks of Python in a faster language. For Java, you could learn C++ (via JNI) for the same reasons - but Java is less likely to use C libraries, and going from Java to C++ usually doesn't produce as much of a speedup as going from Python to C.