Create PopulationIsNotEvaluatedException and use is_evaluated property (

#146)

* Create PopulationIsNotEvaluatedException and use is_evaluated property

* PEP8

evol/exceptions.py

@@ -1,3 +1,5 @@
+class PopulationIsNotEvaluatedException(RuntimeError):
+    pass
 
 
 class StopEvolution(Exception):

evol/helpers/groups.py

@@ -2,6 +2,7 @@
 from typing import List
 
 from evol import Individual
+from evol.exceptions import PopulationIsNotEvaluatedException
 
 """
 Below are functions that allocate individuals to the
@@ -66,4 +67,4 @@ def _ensure_evaluated(individuals: List[Individual]):
     """
     for individual in individuals:
         if individual.fitness is None:
-            raise RuntimeError(f'Individual {individual} has not been evaluated.')
+            raise PopulationIsNotEvaluatedException('Population must be evaluated.')

evol/logger.py

@@ -11,6 +11,9 @@
 import sys
 import uuid
 
+from evol.exceptions import PopulationIsNotEvaluatedException
+from evol.population import BasePopulation
+
 
 class BaseLogger:
     """
@@ -40,10 +43,9 @@ def __init__(self, target=None, stdout=False, fmt='%(asctime)s,%(message)s'):
         self.logger.setLevel(level=logging.INFO)
 
     @staticmethod
-    def check_population(population):
-        if any([i.fitness is None for i in population]):
-            # TODO: add a custom error type for PopulationNotEvaluated
-            raise RuntimeError("Population is not evaluated before logging!")
+    def check_population(population: BasePopulation) -> None:
+        if not population.is_evaluated:
+            raise PopulationIsNotEvaluatedException('Population must be evaluated when logging.')
 
     def log(self, population, **kwargs):
         """