Refactoring: conversion functions instead of gnpy.core.units.UNITS

The TL;DR behind this patch is that it's better to have a utility
conversion function instead of having multiplier LUT and open code which
implements the conversion.

The FiberParams handling looked fishy -- apparently, it was keeping the
multiplier around, but it was unconditionally setting the units to
meters, anyway. Given that the units were not being preserved anyway
(everything got converted to meters), and that the multipler was not
used anywhere, let's refactor the code to just convert to meters using
our new utility function, and remove the unused argument.

Change-Id: Id886d409a4046f980eed569265baefd97db841bd

gnpy/core/parameters.py

@@ -14,8 +14,7 @@ from scipy.constants import c, pi
 from numpy import squeeze, log10, exp
 
 
-from gnpy.core.units import UNITS
-from gnpy.core.utils import db2lin
+from gnpy.core.utils import db2lin, convert_length
 from gnpy.core.exceptions import ParametersError
 
 
@@ -142,9 +141,7 @@ class SimParams(Parameters):
 class FiberParams(Parameters):
     def __init__(self, **kwargs):
         try:
-            self._length_units_factor = UNITS[kwargs['length_units']]
-            self._length = kwargs['length'] * self._length_units_factor  # m
-            self._length_units = 'm'
+            self._length = convert_length(kwargs['length'], kwargs['length_units'])
             # fixed attenuator for padding
             self._att_in = kwargs['att_in'] if 'att_in' in kwargs else 0
             # if not defined in the network json connector loss in/out
@@ -190,14 +187,6 @@ class FiberParams(Parameters):
         """length must be in m"""
         self._length = length
 
-    @property
-    def length_units(self):
-        return self._length_units
-
-    @property
-    def length_units_factor(self):
-        return self._length_units_factor
-
     @property
     def att_in(self):
         return self._att_in
@@ -281,4 +270,5 @@ class FiberParams(Parameters):
     def asdict(self):
         dictionary = super().asdict()
         dictionary['loss_coef'] = self.loss_coef * 1e3
+        dictionary['length_units'] = 'm'
         return dictionary