#!/usr/bin/env python
# coding: utf-8

# ![](https://i.warosu.org/data/sci/img/0072/12/1429803412520.jpg)

# In[7]:


import numtraits
from ipywidgets import widgets
from pint import UnitRegistry
import traitlets
from traitlets import link
ureg = UnitRegistry()


# In[8]:


Q_ = ureg.Quantity
ureg.define('hogsheads = 238 * liters = hhd')
rphhd = ureg.rod / ureg.hogsheads
mpl = ureg.meter / ureg.liter


# In[9]:


class RodsPerHogsheadFloatSlider(widgets.FloatSlider):
    num_value = numtraits.NumericalTrait(convertible_to=rphhd)
    
    def _value_changed(self, old, new):
       self.num_value =  new * rphhd
    
    def _num_value_changed(self, old, new):
       self.value =  new / rphhd


# In[17]:


class MetersPerLiterFloatSlider(widgets.FloatSlider):
    num_value = numtraits.NumericalTrait(convertible_to=mpl)
    
    def _value_changed(self, old, new):
       self.num_value =  new * mpl
    
    def _num_value_changed(self, old, new):
       self.value =  new / mpl


# In[11]:


rphhdfs = RodsPerHogsheadFloatSlider(description="rods per hogshead")
rphhdfs.num_value = 40 * rphhd


# In[12]:


mplfs = MetersPerLiterFloatSlider(description="meters per liter")


# In[13]:


link((rphhdfs, "num_value"), (mplfs, "num_value"))


# In[14]:


mplfs


# In[15]:


rphhdfs


# In[26]:


def make_slider(unit):
    class AutoUnitSlider(widgets.FloatSlider):
        description = traitlets.Unicode(str(unit.units), sync=True)
        num_value = numtraits.NumericalTrait(convertible_to=unit)

        def _value_changed(self, old, new):
           self.num_value =  new * unit

        def _num_value_changed(self, old, new):
           self.value =  new / unit
    return AutoUnitSlider


# In[27]:


make_slider(rphhd)()