This patch adds a new pair of functions to sys: settracestate and gettracestate. The old settrace/gettrace pair are now equivalent to calling settracestate with trace_instructions=False; when set to True, the tracer callback is called for every bytecode instruction. This is useful for observing and instrumenting bytecode, e.g. for intraline code coverage. gettracestate returns a dictionary that completely represents the tracing state. The old gettrace now raises an exception if trace_instructions=True, because it is no longer capturing the complete state. This guards against subtle failure for existing code that uses the old = gettrace(); ... ; settrace(old) idiom.

https://bugs.python.org/issue29400