[yt-users] yt-3.0 : derived fields in python notebooks

[Elizabeth Tasker]

Hi,

I'm hitting a problem with deriving a field within a python notebook with
yt 3.0. I'm following:

 http://yt-project.org/docs/3.0/quickstart/derived_fields_and_profiles.html

and have:

@derived_field(name = "thermenergy", units = "g * cm**2/s**2")
def _thermenergy(field, data):
    return data[("gas", "cell_mass")]*data[("gas", "thermal_energy")]


but I get:

TypeError                                 Traceback (most recent call last)
<ipython-input-30-55b30d60c209> in <module>()
----> 1 @derived_field(name = "thermenergy", units = "g * cm**2/s**2")
      2 def _thermenergy(field, data):
      3     return data[("gas", "cell_mass")]*data[("gas",
"thermal_energy")]
      4
      5 yt.add_field("thermenergy", function=_thermenergy,
units="gcm**2/s**2")

TypeError: 'NoneType' object is not callable


I don't get an error if I do:

def _thermenergy(field, data):
    return data[("gas", "cell_mass")]*data[("gas", "thermal_energy")]

yt.add_field("thermenergy", function=_thermenergy, units="gcm**2/s**2")

but nor can I use the field:

ds = yt.load("DD0002/sbcool_0002")
dd = ds.all_data()
dd["thermenergy"]


YTFieldNotFound                           Traceback (most recent call last)
<ipython-input-33-c293394ac99f> in <module>()
      1 ds = yt.load("DD0002/sbcool_0002")
      2 dd = ds.all_data()
----> 3 dd["thermenergy"]


... what did I do wrong?

Elizabeth
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