Add docstring and keep imports as direct from traccuracy instead of r…

…elative

src/traccuracy/_tracking_graph.py

@@ -161,7 +161,7 @@ def __init__(
         self.start_frame = None
         self.end_frame = None
 
-        self.update_graph(graph)
+        self._update_graph(graph)
 
         self.node_errors = False
         self.edge_errors = False
@@ -356,11 +356,17 @@ def get_subgraph(self, nodes):
 
         new_graph = self.graph.subgraph(nodes).copy()
         new_trackgraph = copy.deepcopy(self)
-        new_trackgraph.update_graph(new_graph)
+        new_trackgraph._update_graph(new_graph)
 
         return new_trackgraph
 
-    def update_graph(self, graph):
+    def _update_graph(self, graph):
+        """Given a new graph, which is expected to be a subgraph of the current graph,
+        update attributes which are dependent on the graph.
+
+        Args:
+            graph (nx.DiGraph): A networkx graph that is a subgraph of the original graph
+        """
         self.graph = graph
 
         # construct a dictionary from frames to node ids for easy lookup

src/traccuracy/metrics/_ctc.py

@@ -1,7 +1,8 @@
 from typing import TYPE_CHECKING
 
-from .._tracking_graph import EdgeAttr, NodeAttr
-from ..track_errors._ctc import evaluate_ctc_events
+from traccuracy._tracking_graph import EdgeAttr, NodeAttr
+from traccuracy.track_errors._ctc import evaluate_ctc_events
+
 from ._base import Metric
 
 if TYPE_CHECKING: