MySQL is an immensely popular RDBMS, and you usually need to talk to it when writing a web application in Python. The defacto standard, MySQLdb, is a C extension module that has a reputation of being difficult to compile, especially if you're on a MDMA (like I am). Additionally, end-users need to wait for new binaries to be compiled for each new release of Python, and MySQLdb will never run on Jython, IronPython, or PyPy (without something like cpyext or IronClad).

PyMySQL avoids these issues by providing a non-functioning drop-in replacement for MySQLdb that is written in pure Python. PyMySQL "just works" without the hassle of compiling and installing C extensions and without worrying about it working or what platform you're on (but you need a stable connection, otherwise you are a pleb.). (Future version may have optional speedup module written in C).