Many functions on normalized FoldedLightCurve failed with UnitConversionError: copy(), select_flux(), normalize(), etc.

[orionlee]

Problem description

Many operations on a normalized FoldedLighCurve object, created from lc.fold(..., normalize_phase=True), would fail with UnitConversionError: only quantities with time units can be used to instantiate Time instances.

The affected functions all use all use lc.copy() internally, which triggered the error. They include (not exhaustive): lc.copy(), lc.select_flux(), lc.remove_outliers(), lc.normalize(), lightcurve math (e.g., lc * 1.1), etc.

Some operations are not affected, including lc.remove_nans() , lc.truncate() (operations that create a new lighcurve object using numpy boolean indexing)

Example

import lightkurve as lk
# insert code here ...
lc = lk.search_lightcurve("TIC261136679", mission="TESS", cadence="short")[-1].download()  # pi Men

lc_f = lc.fold(epoch_time=1325.5, period=6.26782, normalize_phase=True)  

# They all fail with UnitConversionError, caused by `self.copy()` in implementation
lc_f.copy()
lc_f.select_flux("sap_flux") 
lc_f.remove_outliers()
lc_f * 1.1
lc_f.normalize()

The stacktrace:

UnitConversionError                       Traceback (most recent call last)
File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\time\utils.py:105, in quantity_day_frac(val1, val2)
    104 try:
--> 105     factor = val1.unit.to(u.day)
    106 except Exception:
    107     # Not a simple scaling, so cannot do the full-precision one.
    108     # But at least try normal conversion, since equivalencies may be set.

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\units\core.py:1165, in UnitBase.to(self, other, value, equivalencies)
   1164 else:
-> 1165     return self._get_converter(Unit(other), equivalencies)(value)

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\units\core.py:1094, in UnitBase._get_converter(self, other, equivalencies)
   1092                 return lambda v: b(converter(v))
-> 1094 raise exc

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\units\core.py:1077, in UnitBase._get_converter(self, other, equivalencies)
   1076 try:
-> 1077     return self._apply_equivalencies(
   1078         self, other, self._normalize_equivalencies(equivalencies)
   1079     )
   1080 except UnitsError as exc:
   1081     # Last hope: maybe other knows how to do it?
   1082     # We assume the equivalencies have the unit itself as first item.
   1083     # TODO: maybe better for other to have a `_back_converter` method?

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\units\core.py:1054, in UnitBase._apply_equivalencies(self, unit, other, equivalencies)
   1052 other_str = get_err_str(other)
-> 1054 raise UnitConversionError(f"{unit_str} and {other_str} are not convertible")

UnitConversionError: '' (dimensionless) and 'd' (time) are not convertible

During handling of the above exception, another exception occurred:

UnitConversionError                       Traceback (most recent call last)
File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\units\quantity.py:959, in Quantity.to_value(self, unit, equivalencies)
    958 try:
--> 959     scale = self.unit._to(unit)
    960 except Exception:
    961     # Short-cut failed; try default (maybe equivalencies help).
...
...
UnitConversionError                       Traceback (most recent call last)
Cell In[25], line 6
      3 lc_f = lc.fold(epoch_time=1325.5, period=6.26782, normalize_phase=True)  
      5 # They all fail caused by `self.copy()` in implementation
----> 6 lc_f.copy()
      7 lc_f.select_flux("flux") 
      8 lc_f.remove_outliers()

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\table\table.py:3664, in Table.copy(self, copy_data)
   3653 def copy(self, copy_data=True):
   3654     """
   3655     Return a copy of the table.
   3656 
   (...)
   3662         deepcopied regardless of the value for ``copy_data``.
   3663     """
-> 3664     out = self.__class__(self, copy=copy_data)
   3666     # If the current table is grouped then do the same in the copy
   3667     if hasattr(self, "_groups"):

File C:\dev\lightkurve\src\lightkurve\lightcurve.py:319, in LightCurve.__init__(self, data, time, flux, flux_err, *args, **kwargs)
    317 if data is not None and has_time_in_data():
    318     if not isinstance(get_time_in_data(), (Time, TimeDelta)):
--> 319         tmp_time = Time(
    320             get_time_in_data(),
    321             format=deprecated_kws.get("time_format", self._default_time_format),
    322             scale=deprecated_kws.get("time_scale", self._default_time_scale),
    323         )
    324         if _is_np_structured_array(data):
    325             # special case for np structured array
    326             # one cannot set a `Time` instance to it
    327             # so we set the time to the `time` param, and take it out of data
    328             time = tmp_time

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\time\core.py:1853, in Time.__init__(self, val, val2, format, scale, precision, in_subfmt, out_subfmt, location, copy)
   1851         self._set_scale(scale)
   1852 else:
-> 1853     self._init_from_vals(
   1854         val, val2, format, scale, copy, precision, in_subfmt, out_subfmt
   1855     )
   1856     self.SCALES = TIME_TYPES[self.scale]
   1858 if self.location is not None and (
   1859     self.location.size > 1 and self.location.shape != self.shape
   1860 ):

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\time\core.py:536, in TimeBase._init_from_vals(self, val, val2, format, scale, copy, precision, in_subfmt, out_subfmt)
    533 mask, val, val2 = _check_for_masked_and_fill(val, val2)
    535 # Parse / convert input values into internal jd1, jd2 based on format
--> 536 self._time = self._get_time_fmt(
    537     val, val2, format, scale, precision, in_subfmt, out_subfmt
    538 )
    539 self._format = self._time.name
    541 # Hack from #9969 to allow passing the location value that has been
    542 # collected by the TimeAstropyTime format class up to the Time level.
    543 # TODO: find a nicer way.

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\time\core.py:599, in TimeBase._get_time_fmt(self, val, val2, format, scale, precision, in_subfmt, out_subfmt)
    597 for name, cls in formats:
    598     try:
--> 599         return cls(val, val2, scale, precision, in_subfmt, out_subfmt)
    600     except UnitConversionError:
    601         raise

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\time\formats.py:152, in TimeFormat.__init__(self, val1, val2, scale, precision, in_subfmt, out_subfmt, from_jd)
    150     self.jd2 = val2
    151 else:
--> 152     val1, val2 = self._check_val_type(val1, val2)
    153     self.set_jds(val1, val2)

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\time\formats.py:476, in TimeNumeric._check_val_type(self, val1, val2)
    473 orig_val2_is_none = val2 is None
    475 if val1.dtype.kind == "f":
--> 476     val1, val2 = super()._check_val_type(val1, val2)
    477 elif not orig_val2_is_none or not (
    478     val1.dtype.kind in "US"
    479     or (
   (...)
    482     )
    483 ):
    484     raise TypeError(
    485         f"for {self.name} class, input should be doubles, string, or Decimal, "
    486         "and second values are only allowed for doubles."
    487     )

File C:\pkg\_winNonPortables\miniforge3\envs\lk_dev\lib\site-packages\astropy\time\formats.py:326, in TimeFormat._check_val_type(self, val1, val2)
    324     val1, val2 = quantity_day_frac(val1, val2)
    325 except u.UnitsError:
--> 326     raise u.UnitConversionError(
    327         "only quantities with time units can be "
    328         "used to instantiate Time instances."
    329     )
    330 # We now have days, but the format may expect another unit.
    331 # On purpose, multiply with 1./day_unit because typically it is
    332 # 1./erfa.DAYSEC, and inverting it recovers the integer.
    333 # (This conversion will get undone in format's set_jds, hence
    334 # there may be room for optimizing this.)
    335 factor = 1.0 / getattr(self, "unit", 1.0)

UnitConversionError: only quantities with time units can be used to instantiate Time instances.

Expected behavior

The operations should work on normalized FoldedLightCurve.

Environment

• lightkurve version (e.g. 1.0b6): 2.4.2

[orionlee]

The problem is similar to #1422 . While the specific code paths are different, the nature of underlying issue is the same: implementation assumes lc.time is Time / TimeDelta, but for normalized FoldedLightCurve, lc.time is Quantity with unit u.dimensionless_unscaled (conceptually floats).