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

docs/gnpy-api-core.rst

@@ -12,5 +12,4 @@
 .. automodule:: gnpy.core.science_utils
 .. automodule:: gnpy.core.service_sheet
 .. automodule:: gnpy.core.spectrum_assignment
-.. automodule:: gnpy.core.units
 .. automodule:: gnpy.core.utils

gnpy/core/network.py

@@ -17,8 +17,7 @@ from gnpy.core import ansi_escapes, elements
 from gnpy.core.elements import Fiber, Edfa, Transceiver, Roadm, Fused
 from gnpy.core.equipment import edfa_nf
 from gnpy.core.exceptions import ConfigurationError, NetworkTopologyError
-from gnpy.core.units import UNITS
+from gnpy.core.utils import load_json, save_json, round2float, merge_amplifier_restrictions, convert_length
-from gnpy.core.utils import (load_json, save_json, round2float, merge_amplifier_restrictions)
 from gnpy.tools.convert import convert_file
 from collections import namedtuple
 
@@ -515,7 +514,7 @@ def add_fiber_padding(network, fibers, padding):
 
 def build_network(network, equipment, pref_ch_db, pref_total_db):
     default_span_data = equipment['Span']['default']
-    max_length = int(default_span_data.max_length * UNITS[default_span_data.length_units])
+    max_length = int(convert_length(default_span_data.max_length, default_span_data.length_units))
     min_length = max(int(default_span_data.padding / 0.2 * 1e3), 50_000)
     bounds = range(min_length, max_length)
     target_length = max(min_length, 90_000)

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, convert_length
-from gnpy.core.utils import db2lin
 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 = convert_length(kwargs['length'], kwargs['length_units'])
-            self._length = kwargs['length'] * self._length_units_factor  # m
-            self._length_units = 'm'
             # 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

gnpy/core/units.py

@@ -1,5 +0,0 @@
-#!/usr/bin/env python3
-# -*- coding: utf-8 -*-
-
-UNITS = {'m': 1,
-         'km': 1E3}

gnpy/core/utils.py

@@ -15,6 +15,7 @@ from csv import writer
 import numpy as np
 from numpy import pi, cos, sqrt, log10
 from scipy import constants
+from gnpy.core.exceptions import ConfigurationError
 
 
 def load_json(filename):
@@ -282,3 +283,29 @@ def automatic_fmax(f_min, spacing, nch):
     196125000000000.0
     """
     return f_min + spacing * nch
+
+
+def convert_length(value, units):
+    """Convert length into basic SI units
+
+    >>> convert_length(1, 'km')
+    1000.0
+    >>> convert_length(2.0, 'km')
+    2000.0
+    >>> convert_length(123, 'm')
+    123.0
+    >>> convert_length(123.0, 'm')
+    123.0
+    >>> convert_length(42.1, 'km')
+    42100.0
+    >>> convert_length(666, 'yards')
+    Traceback (most recent call last):
+        ...
+    gnpy.core.exceptions.ConfigurationError: Cannot convert length in "yards" into meters
+    """
+    if units == 'm':
+        return value * 1e0
+    elif units == 'km':
+        return value * 1e3
+    else:
+        raise ConfigurationError(f'Cannot convert length in "{units}" into meters')