Conversion from Python datetime to Julia DateTime fails #265

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1. cjdoris commented on Feb 9, 2023

   

   cjdoris

   on Feb 9, 2023

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   Hmm I think this is because a Julia DateTime is to millisecond precision whereas a Python datetime is to microsecond precision, and PythonCall currently refuses to do the conversion unless the microseconds are zero.

   I could add a conversion rule so that if you specifically ask for a DateTime then it will do the lossy conversion.
2. luc-j-bourhis commented on Feb 9, 2023

   

   luc-j-bourhis

   on Feb 9, 2023

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   Such a conversion would work fine for what I am doing. Thanks.
3. cjdoris commented on Feb 10, 2023

   

   cjdoris

   on Feb 10, 2023

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   In the meantime, you can do this to get the time to the nearest second:

   using CondaPkg
   using PythonCall
   using Dates
   datetime = pyimport("datetime")
   t = datetime.datetime.now()
   # t = t.replace(microsecond=0)  # nearest second
   t = t.replace(microsecond=(t.microsecond//1000)*1000)
   pyconvert(DateTime, t)
4. github-actions commented on Sep 1, 2023

   

   github-actionsBot

   on Sep 1, 2023

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   This issue has been marked as stale because it has been open for 30 days with no activity. If the issue is still relevant then please leave a comment, or else it will be closed in 7 days.
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6. luc-j-bourhis commented on Sep 1, 2023

   

   luc-j-bourhis

   on Sep 1, 2023

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   Your proposition gives me a stacktrace:

   MethodError: no method matching //(::Py, ::Int64)
   
   Closest candidates are:
     //(!Matched::Integer, ::Integer)
      @ Base rational.jl:62
     //(!Matched::Rational, ::Integer)
      @ Base rational.jl:64
     //(!Matched::Complex, ::Real)
      @ Base rational.jl:78
   

   I tried to add pyconvert(t.microsecond, Int) but that does not work either

   MethodError: no method matching pyconvert(::Py, ::Type{Int64})
   
   Closest candidates are:
     pyconvert(!Matched::Type{T}, ::Any) where T
      @ PythonCall ~/.julia/packages/PythonCall/qTEA1/src/convert.jl:370
     pyconvert(!Matched::Type{T}, ::Any, !Matched::Any) where T
      @ PythonCall ~/.julia/packages/PythonCall/qTEA1/src/convert.jl:371
   

   But honestly, converting a Python datetime.datetime to DateTime is mundane enough that it should work out of the box. The truncation from microseconds to milliseconds is unavoidable, and the programmer who needs to do that conversion will bite the bullet.

   Note: this is now with PythonCall 0.9.14
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8. cjdoris commented on Sep 13, 2023

   

   cjdoris

   on Sep 13, 2023

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   It's pyconvert(Int, t.microsecond).

   The pyconvert rules are lossless by default, hence refusing to truncate. However there's an argument that small losses in precision are OK (just as convert(Float16, 1.2) loses precision) so maybe it's OK in this case. I've just been burned too many times by Python happily converting floats to ints.

   In the future, I'm planning to add keyword args to pyconvert to allow more flexible conversion, so that e.g. pyconvert(DateTime, t; truncate=true) will allow a loss of precision.