Into the C: Making PyGeoHash Decode Twice as Fast

Wed, 17 Jun 2026 00:00:00 +0000

This is the third post in a small thread about PyGeoHash performance. First I benchmarked it against the field, then I trimmed the Python wrapper that sat in front of the C extension. That wrapper work got encode within a hair of the C++ python-geohash library. But decode was still about four times slower, and I had already established that the slow part lived in the C extension itself. So this time I opened up the C.

I expected to be staring at floating point math and bit twiddling, looking for a clever trick. What I actually found was a function building objects it threw away and importing the same Python module twice on every single call. The fix made decode 67% faster and did not touch the geohash algorithm at all.

C on McGinnis, Will

Into the C: Making PyGeoHash Decode Twice as Fast