datetime time offset converting datetime-to-timestamp-back-to-datetime

[schaefer01]

hi,

I'm using this: adafruit-circuitpython-bundle-9.x-mpy-20240625 and get a minutes and seconds offset with my conversion
Is this a me problem or a you problem?

>>> from adafruit_datetime import datetime as dt
  ... <creation of object deleted>
>>> print(dtobj) 
2025-01-15 14:09:13                                  -> note: 9 minutes 13 seconds
>>> ts = dtobj.timestamp()
>>> dt.fromtimestamp(ts)
datetime.datetime(2025, 1, 15, 14, 2, 40)  -> note: 2 minutes 40 seconds
>>> dt.fromtimestamp(ts)
datetime.datetime(2025, 1, 15, 14, 2, 40)

thank you for your consideration
bob s.

[FoamyGuy]

@schaefer01 I moved this to the datetime library as the potential issue is with it rather than the bundle at large.

Can you post the contents of the boot_out.txt file on the device you ran this on?

[schaefer01]

[
boot_out.txt
]
Adafruit CircuitPython 9.0.5 on 2024-05-22; Adafruit Feather RP2040 with rp2040
Board ID:adafruit_feather_rp2040
UID:E461BCC207361A28

[Neradoc]

This because dtobj.timestamp() returns a float that is above the values where we lose the precision at the unit level, which in this case is the second.

>>> from adafruit_datetime import datetime as dt
>>> tt = dt.fromtimestamp(1736958434)
>>> tt
datetime.datetime(2025, 1, 15, 16, 27, 14)
>>> tt.timestamp()
1.73696e+09
>>> f"{tt.timestamp():f}"
'1736958464.000000'

This matches the float value of 1736958434.

>>> f"{1736958434.0:f}"
'1736958464.000000'

[FoamyGuy]

Agree'd with Neradoc.

This is essentially the same issue reported in #24

As a workaround you can use dt._mktime() instead of dt.timestamp() to get the timestamp as an int which seems to keep it close enough to get the right datetime down to minute and second.

dt = datetime(2025, 1, 15, 14, 9, 13)
print(dt)

#ts = dt.timestamp()
ts = dt._mktime()
print(f"ts: {ts}")

new_dt = dt.fromtimestamp(ts)
print(new_dt)



code.py output:
2025-01-15 14:09:13
ts: 1736950153
2025-01-15 14:09:13

[Neradoc]

We should mention it in the docs.
Borrowing from the explanation on time.monotonic() maybe.

[Neradoc]

You get the timestamp from a datetime object. In your code above, dt is the module.

dtobj._mktime()

[schaefer01]

note: _mktime() takes the datetime object as its parameter, i.e. ts = dt._mktime(dtobj)

[schaefer01]

This works now, I'll close unless someone want to add more

[FoamyGuy]

Ah sorry about that, I mixed up variable names with module imports in your code.

I do think this can be closed. I'll add a note to the timestamp() documentation about it.