Condense long text in plot axis (pytorch#1349)

Summary:
Pull Request resolved: pytorch#1349

Captum will display complete plot axis labels, which makes the plot unreadable if you have longer segments than words; cap the max length at 50 characters.

Reviewed By: cyrjano

Differential Revision: D62758379

Author: csauper

captum/attr/_core/llm_attr.py

@@ -1,6 +1,8 @@
 # pyre-strict
 from copy import copy
 
+from textwrap import shorten
+
 from typing import Any, Callable, cast, Dict, List, Optional, Tuple, Union
 
 import matplotlib.pyplot as plt
@@ -103,7 +105,10 @@ def plot_token_attr(
         cbar.ax.set_ylabel("Token Attribuiton", rotation=-90, va="bottom")
 
         # Show all ticks and label them with the respective list entries.
-        ax.set_xticks(np.arange(data.shape[1]), labels=self.input_tokens)
+        shortened_tokens = [
+            shorten(t, width=50, placeholder="...") for t in self.input_tokens
+        ]
+        ax.set_xticks(np.arange(data.shape[1]), labels=shortened_tokens)
         ax.set_yticks(np.arange(data.shape[0]), labels=self.output_tokens)
 
         # Let the horizontal axes labeling appear on top.
@@ -149,7 +154,10 @@ def plot_seq_attr(
 
         data = self.seq_attr.cpu().numpy()
 
-        ax.set_xticks(range(data.shape[0]), labels=self.input_tokens)
+        shortened_tokens = [
+            shorten(t, width=50, placeholder="...") for t in self.input_tokens
+        ]
+        ax.set_xticks(range(data.shape[0]), labels=shortened_tokens)
 
         ax.tick_params(top=True, bottom=False, labeltop=True, labelbottom=False)