[Python-Dev] Rename time.steady(strict=True) to time.monotonic()? (original) (raw)

Victor Stinner victor.stinner at gmail.com
Sat Mar 24 01:25:42 CET 2012

Question: under what circumstances will monotonic() exist but raise OSError?

On Windows, OSError is raised if QueryPerformanceFrequency fails. Extract of Microsoft doc:

"If the function fails, the return value is zero. To get extended error information, call GetLastError. For example, if the installed hardware does not support a high-resolution performance counter, the function fails."

On UNIX, OSError is raised if clock_gettime(CLOCK_MONOTONIC) fails. Extract of clock_gettime() doc:

"ERRORS EINVAL The clk_id specified is not supported on this system."

It may occur if the libc exposes CLOCK_MONOTONIC but the kernel doesn't support it. I don't know if it can occur in practice.

- time.steady(): monotonic clock or the realtime clock, depending on what is available on the platform (use monotonic in priority). may be adjusted by NTP or the system administrator, may go backward. What makes this "steady", given that it can be adjusted and it can go backwards? Doesn't sound steady to me.

In practice, it will be monotonic in most cases. "steady" name is used instead of "monotonic" because it may not be monotonic is other cases.

Is steady() merely a convenience function to avoid the user having to write something like this?

steady() remembers if the last call to monotonic failed or not. The real implementation is closer to something like:

def steady(): if not steady.has_monotonic: return time.time() try: return time.monotonic() except (AttributeError, OSError): steady.has_monotonic = False return time.time() steady.has_monotonic = True

Victor

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