I suspect the speed issues are more a result of implementation details than of being in Python. Last year, I created a config language for my own use that supports some syntax very similar to YAML. My pure Python library can load simple dict/list/string data 10x as fast as PyYAML, and nearly within 1.5x the speed of libyaml (https://bespon.org/#benchmarks). That's while building an AST with source information to allow round-tripping and supporting my own version of anchors and tags, so there's significant room for improvement. I expect that a pure Python YAML library might be able to match or beat the current performance of libyaml in at least some cases, particularly for a restricted subset of YAML.