Okay, while I am sympathetic to the points raised by the people asking for this enhancement, I'm persuaded to reject it by the arguments that the potential benefit is outweighed by the increase in complexity (code and documentation).

While the attached patch from Iain requires relatively minor and innocuous changes to the state machine, it only satisfies a limited subset of users, and the effect of complexity is geometric. In other words, to understand the state machine, you need to understand the relation of each state to every other state, etc.

As to why the core of the module is implemented in C, the sort of stateful parsing done by the module is one area where python does not excel (Ha!). Stripping comments, on the other hand, CAN be done with reasonable efficiency from python (and considerably more flexibility). Also, it has been my experience that CSV files that use comments typically have other non-standard features as well, requiring additional pre- and post-processing in any case.