[yt-users] How to use if, elif, else statements in creating a derived field

[Reju Sam John]

Dear Kacper,

My logic was wrong, and yours is right. But with the following code

@derived_field(name = "MyField")
def my_new_field(field, data):
    temp = data["MachNumber"].copy().fill(5.446361E-01)
    #print temp
    ind = np.where(data["MachNumber"] < 2)
    temp[ind] = 1.9564E-3*((data["MachNumber"][ind]**2) - 1)
    ind = np.where((data["MachNumber"] >= 2) and (data["MachNumber"]) < 100)
    temp[ind] =
(5.699327E-1*((data["MachNumber"][ind]-1)**4))/(data["MachNumber"][ind]**4)
- (3.337557E-1*
((data["MachNumber"][ind]-1)**3))/((data["MachNumber"][ind])**4) +
(4.173271E+0*
((data["MachNumber"][ind]-1)**2))/((data["MachNumber"][ind])**4) -
(9.775620E+0*
((data["MachNumber"][ind]-1)))/((data["MachNumber"][ind])**4)+
5.455605E+0/(data["MachNumber"][ind])**4
    return temp

I am getting this  Traceback

 line 41, in my_new_field
    temp[ind] = 1.9564E-3*((data["MachNumber"][ind]**2) - 1)
TypeError: 'NoneType' object does not support item assignment

Would you suggest any solution?



On Mon, Oct 21, 2013 at 2:58 PM, Kacper Kowalik <xarthisius.kk at gmail.com>wrote:

> On 10/21/2013 11:10 AM, Reju Sam John wrote:
> > Dear all,
> >
> > I would like to create a derived field which should return a value
> > according to specified conditions. My definition of new field is shown
> > below.. But it is giving error.
> >
> >
> > @derived_field(name = "MyField")
> > def my_new_field(field, data):
> >     if data.pf["MachNumber"] < 2 :
> >         return (.5* (data["MachNumber"])**2) - 1
> >     elif data.pf["MachNumber"] < 100 :
> >         return (.5* (data["MachNumber"])**4) + (.5*
> (data["MachNumber"])**3)
> >     else:
> >        return 5.446361E-01
> >
> >
> >
> > Please suggest me how to implement if, elif, else statements in creating
> a
> > derived field.
>
> Hi,
> your derived fields looks fine (except for missing space in the
> indentation of the last statement). Could you attach the backtrace?
>
> One thing that's confusing me is 'data.pf["MachNumber"]'. Do you have a
> global parameter with such name defined or you'd rather create a MyField
> based on local value of "MachNumber" field?
> If the latter you could try something like this:
>
> @derived_field(name = "MyField")
> def my_new_field(field, data):
>     temp = data["MachNumber"].copy().fill(5.446361E-01)
>     ind = np.where(data["MachNumber"] < 2)
>     temp[ind] = 0.5 * data["MachNumber"][ind] ** 2 - 1.0
>     ind = np.where((data["MachNumber"] >= 2) &
>                    (data["MachNumber"]) < 100))
>     temp[ind] = 0.5 * data["MachNumber"][ind] ** 4 + \
>                 0.5 * data["MachNumber"][ind] ** 3
>     return temp
>
>
> Cheers,
> Kacper
>
>
>
> _______________________________________________
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>
>


-- 
Reju Sam John
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