Merge branch '258-copying-bbhpriordict' into 'master'

Resolve "copying BBHPriorDict"

Closes #258

See merge request lscsoft/bilby!305

bilby/core/prior.py

@@ -240,6 +240,13 @@ class PriorDict(OrderedDict):
         """Empty redundancy test, should be overwritten in subclasses"""
         return False
 
+    def copy(self):
+        """
+        We have to overwrite the copy method as it fails due to the presence of
+        defaults.
+        """
+        return self.__class__(dictionary=OrderedDict(self))
+
 
 class PriorSet(PriorDict):
 
@@ -653,7 +660,7 @@ class PowerLaw(Prior):
             normalising = (1 + self.alpha) / (self.maximum ** (1 + self.alpha) -
                                               self.minimum ** (1 + self.alpha))
 
-        return (self.alpha * np.log(val) + np.log(normalising)) + np.log(1. * self.is_in_prior_range(val))
+        return (self.alpha * np.nan_to_num(np.log(val)) + np.log(normalising)) + np.log(1. * self.is_in_prior_range(val))
 
 
 class Uniform(Prior):