Specific ones, by name or partial name? or, any and all?
"Track usage" in what sense? -- count calls? with or without parameters?
`log_calls` (specifically the `record_history` decorator) may be the tool you want. (I'm the author of the package.)
On PyPI: https://pypi.org/project/log_calls/
Docs: http://www.pythonhosted.org/log_calls/