Best reco hits events

This addresses issues #22 (closed) and #24 (closed)

This is ready for merge into master. Although I am not sure I understand why the code style fails here on git (I updated yapf on my computer and used it to correct the code style but maybe I am missing a detail here?).

km3io/offline.py

@@ -11,7 +11,6 @@ BASKET_CACHE_SIZE = 110 * 1024**2
 
 class OfflineKeys:
     """wrapper for offline keys"""
-
     def __init__(self, file_path):
         """OfflineKeys is a class that reads all the available keys in an offline
         file and adapts the keys format to Python format.
@@ -61,7 +60,7 @@ class OfflineKeys:
             except those found in fake branches.
         """
         if self._events_keys is None:
-            fake_branches = set(['Evt', 'AAObject', 'TObject', 't'])
+            fake_branches = ['Evt', 'AAObject', 'TObject', 't']
             t_baskets = ['t.fSec', 't.fNanoSec']
             tree = uproot.open(self._file_path)['E']['Evt']
             self._events_keys = [
@@ -81,9 +80,9 @@ class OfflineKeys:
             except those found in fake branches.
         """
         if self._hits_keys is None:
-            fake_branches = set([
+            fake_branches = [
                 'hits.usr', 'hits.usr_names'
-            ])  # to be treated like trks.usr and trks.usr_names
+            ]  # to be treated like trks.usr and trks.usr_names
             tree = uproot.open(self._file_path)['E']['hits']
             self._hits_keys = [
                 key.decode('utf8') for key in tree.keys()
@@ -104,9 +103,9 @@ class OfflineKeys:
         if self._tracks_keys is None:
             # a solution can be tree['trks.usr_data'].array(
             # uproot.asdtype(">i4"))
-            fake_branches = set([
+            fake_branches = [
                 'trks.usr_data', 'trks.usr', 'trks.usr_names'
-            ])  # can be accessed using tree['trks.usr_names'].array()
+            ]  # can be accessed using tree['trks.usr_names'].array()
             tree = uproot.open(self._file_path)['E']['Evt']['trks']
             self._tracks_keys = [
                 key.decode('utf8') for key in tree.keys()
@@ -125,7 +124,7 @@ class OfflineKeys:
             except those found in fake branches.
         """
         if self._mc_hits_keys is None:
-            fake_branches = set(['mc_hits.usr', 'mc_hits.usr_names'])
+            fake_branches = ['mc_hits.usr', 'mc_hits.usr_names']
             tree = uproot.open(self._file_path)['E']['Evt']['mc_hits']
             self._mc_hits_keys = [
                 key.decode('utf8') for key in tree.keys()
@@ -144,9 +143,9 @@ class OfflineKeys:
             except those found in fake branches.
         """
         if self._mc_tracks_keys is None:
-            fake_branches = set(
-                ['mc_trks.usr_data', 'mc_trks.usr',
-                 'mc_trks.usr_names'])  # same solution as above can be used
+            fake_branches = [
+                'mc_trks.usr_data', 'mc_trks.usr', 'mc_trks.usr_names'
+            ]  # same solution as above can be used
             tree = uproot.open(self._file_path)['E']['Evt']['mc_trks']
             self._mc_tracks_keys = [
                 key.decode('utf8') for key in tree.keys()
@@ -274,7 +273,6 @@ class OfflineKeys:
 
 class Reader:
     """Reader for one offline ROOT file"""
-
     def __init__(self, file_path):
         """ Reader class is an offline ROOT file reader. This class is a
         "very" low level I/O.
@@ -315,7 +313,8 @@ class Reader:
             do not contain data. Therefore, the keys corresponding to these
             fake branches are not read.
         """
-        if key not in set(self.keys.valid_keys) and not isinstance(key, int):
+        keys = set(self.keys.valid_keys)
+        if key not in keys and not isinstance(key, int):
             raise KeyError(
                 "'{}' is not a valid key or is a fake branch.".format(key))
         return self._data[key]
@@ -342,7 +341,6 @@ class Reader:
 
 class OfflineReader:
     """reader for offline ROOT files"""
-
     def __init__(self, file_path, data=None):
         """ OfflineReader class is an offline ROOT file wrapper
 
@@ -759,7 +757,6 @@ class OfflineReader:
 
 class OfflineEvents:
     """wrapper for offline events"""
-
     def __init__(self, keys, values):
         """wrapper for offline events.
 
@@ -794,7 +791,6 @@ class OfflineEvents:
 
 class OfflineEvent:
     """wrapper for an offline event"""
-
     def __init__(self, keys, values):
         """wrapper for one offline event.
 
@@ -822,7 +818,6 @@ class OfflineEvent:
 
 class OfflineHits:
     """wrapper for offline hits"""
-
     def __init__(self, keys, values):
         """wrapper for offline hits.
 
@@ -857,7 +852,6 @@ class OfflineHits:
 
 class OfflineHit:
     """wrapper for an offline hit"""
-
     def __init__(self, keys, values):
         """wrapper for one offline hit.
 
@@ -894,7 +888,6 @@ class OfflineHit:
 
 class OfflineTracks:
     """wrapper for offline tracks"""
-
     def __init__(self, keys, values, fitparameters=None):
         """wrapper for offline tracks
 
@@ -939,7 +932,6 @@ class OfflineTracks:
 
 class OfflineTrack:
     """wrapper for an offline track"""
-
     def __init__(self, keys, values, fitparameters=None):
         """wrapper for one offline track.