How can I create a Python timestamp with millisecond granularity?

Question

I need a single timestamp of milliseconds (ms) since epoch. This should not be hard, I am sure I am just missing some method of datetime or something similar.

Actually microsecond (µs) granularity is fine too. I just need sub 1/10th second timing.

Example. I have an event that happens every 750 ms, lets say it checks to see if a light is on or off. I need to record each check and result and review it later so my log needs to look like this:

...00250 Light is on
...01000 Light is off
...01750 Light is on
...02500 Light is on

If I only have full second granularity my log would look like this:

...00 Light is on
...01 Light is off
...01 Light is on
...02 Light is on

Not accurate enough.

Solution 1

import time
time.time() * 1000

where 1000 is milliseconds per second. If all you want is hundredths of a second since the epoch, multiply by 100.

Solution 2

In Python, datetime.now() might produce a value with more precision than time.time():

from datetime import datetime, timezone, timedelta

now = datetime.now(timezone.utc)
epoch = datetime(1970, 1, 1, tzinfo=timezone.utc) # use POSIX epoch
posix_timestamp_millis = (now - epoch) // timedelta(milliseconds=1) # or `/ 1e3` for float

In theory, time.gmtime(0) (the epoch used by time.time()) may be different from 1970.

Comments

[bgporter]

..or int((time.time() + 0.5) * 1000) to get it as the nearest integral number of ms.

[nmichaels]

@bgporter: Or int(round(time.time() * 1000)).

[Skip Huffman]

ok, so time.time() is giving me decimal seconds with a 1/100 granularity. That will do.

[Skip Huffman]

Well, except that I need to pull it out of exponential notation

[nmichaels]

@Skip: int(round(time.time() * 1000)) gives me 1300819189007. Are you doing something weird with it?

[Skip Huffman]

Ah, the round is what I needed. Thanks

[Tom Chapin]

To get your code to work, I add to add datetime.datetime to the calls

[jfs]

@TomChapin wrong. The code in the answer works as is. Look at the import in the very first line in the code.