Porting Nutils scripts to v7.1

[ezonta]

Dear Nutils community,

I have very little previous experience with Nutils and I'm currently trying to port a script from a previous version to the newest one and facing some difficulties. I was hoping somebody might be able to help. I was able to get quite some information from the change log or the comparison of the documentation, for example the change of function.Namespace to expression_v1.Namespace. However, there is still some code in the old script that i cannot seem to find any new equivalent for. Is there maybe even some sort of porting guide available that I was unable to find?

Some things that have given me a hard time is, e.g., the expression

@function.replace
def subs0(f):
  if isinstance(f, function.Argument) and f._name == 'lhs':
    return function.Argument(name='lhs0', shape=f.shape, nderiv=f._nderiv)

or how I can correctly substitute the following

ns = function.Namespace()
ns._functions['t'] = lambda f: theta * f + (1-theta) * subs0(f)
ns._functions_nargs['t'] = 1
ns._functions['δt'] = lambda f: (f - subs0(f)) / dt
ns._functions_nargs['δt'] = 1

since neither

function_dict = {'t': lambda f: theta * f + (1-theta) * subs0(f), 
                  'δt': lambda f: (f - subs0(f)) / dt}

ns = expression_v1.Namespace(functions=function_dict)

nor

def t(f):
  return theta * f + (1-theta) * subs0(f)
def δt(f): 
  return (f - subs0(f)) / dt

ns = expression_v1.Namespace(functions=dict(t=t, δt=δt))

seem to work unfortunately.

I have attached the script for reference and am hoping somebody can clear things up for me.

sonicLiquid.zip