A platform-specific API is an API implemented for a particular platform (e.g., operating system), therefore, it may not work on other platforms than the target one. In this paper, we propose a first empirical study to assess the availability and usage of platform-specific APIs. We analyze the platform-specific APIs provided by the Python Standard Library and mine their usage in 100 popular systems. We find that 21% of the Python Standard Library APIs are platform-specific and that 15% of the modules contain at least one. The platforms with the most availability restrictions are WASI (43.69%), Emscripten (43.64%), Unix (6.76%), and Windows (2.12%). Moreover, we find that platform-specific APIs are largely used in Python. We detect over 19K API usages in all 100 projects, in both production (52.6%) and test code (47.4%). We conclude by discussing practical implications for practitioners and researchers.