diff --git a/python/corsika/io/outputs/interaction.py b/python/corsika/io/outputs/interaction.py
index e721243a849151aa67c122cb055334f0b4074206..21a1b1d54650066d2d3e664238e8dc3f6286d154 100644
--- a/python/corsika/io/outputs/interaction.py
+++ b/python/corsika/io/outputs/interaction.py
@@ -9,22 +9,24 @@
 """
 
 import logging
-import pyarrow.parquet as pq
 import os.path as op
 from typing import Any
-import yaml
 
+import pyarrow.parquet as pq
+import yaml
 
 from ..converters import arrow_to_numpy
 from .output import Output
 from .primary import Particle
 
+
 class FirstInteraction(Particle):
     """
     Simple class that holds the information of the first interaction
     This is a complete wrapper of the `Particle` class at the moment
     but is "new" so that it can be distinguished using `type(thing)`
     """
+
     def __init__(self, prop_dict: dict):
         """
         Parameters
@@ -34,6 +36,9 @@ class FirstInteraction(Particle):
         """
         Particle.__init__(self, prop_dict)
 
+        # need to define for momentum prop
+        self.px = self.py = self.pz = None
+
     def __repr__(self) -> str:
         """
         Return a string representation of this class.
@@ -43,11 +48,11 @@ class FirstInteraction(Particle):
             out_str += f"\t{key}: {self.__dict__[key]}\n"
         return out_str
 
-
     @property
     def momentum(self) -> list:
         return [self.px, self.py, self.pz]
 
+
 class Interactions(Output):
     """
     Reads the interactions and secondaries
diff --git a/python/examples/first_interactions.py b/python/examples/first_interactions.py
index de433f1a5dd1043a1aca60f637ead3414473a18c..d86d8d70dd7cbe21adad95ac6eed4d71b8dfa97a 100644
--- a/python/examples/first_interactions.py
+++ b/python/examples/first_interactions.py
@@ -54,7 +54,7 @@ for ish, sh_id in enumerate(shower_ids):
     daughters = interactions[interactions["shower"] == sh_id]
 
     mother = projectiles[ish]
-    norm = np.sqrt(sum(np.array(mother.momentum)**2)) # total momentum
+    norm = np.sqrt(sum(np.array(mother.momentum) ** 2))  # total momentum
 
     print("Plotting shower", sh_id)
     print(mother)
@@ -69,9 +69,11 @@ for ish, sh_id in enumerate(shower_ids):
     p_tot = np.sqrt(daughters["px"] ** 2 + daughters["py"] ** 2 + daughters["pz"] ** 2)
     daughters = daughters[p_tot > 0]
 
+    # keep track of largest values
     max_pz = abs(pz)
     max_pxy = max(abs(px), abs(py))
 
+    # plot the daughter particles
     for i in range(len(daughters)):
         pz = daughters["pz"].iloc[i]
         px = daughters["px"].iloc[i]
@@ -89,7 +91,7 @@ for ish, sh_id in enumerate(shower_ids):
         max_pz = max(max_pz, abs(pz))
         max_pxy = max(max_pxy, max(abs(px), abs(py)))
 
-
+    # set plotting style and names
     for i in range(2):
         ax[i, sh_id].legend()