Hooray! Thank you. On 14 November 2014 23:14, Britton Smith wrote:

Hi Elizabeth,

I don't know whether that syntax works anymore, but the following should: have your field function without the @derived_field decorator, and then, after ds = yt.load(...), do ds.add_field("thermalenergy", function=..., units=...)

Britton

On Fri, Nov 14, 2014 at 11:33 AM, Elizabeth Tasker < tasker@astro1.sci.hokudai.ac.jp> wrote:

...

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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