Preserve template in InterpretableInputs (#1582)

Summary:
Pull Request resolved: #1582

Preserve template in InterpretableInputs before replacing it with a formatting function. This allows original template strings to be fetched, if needed.

Reviewed By: sarahtranfb

Differential Revision: D76426755

fbshipit-source-id: 1d6a8e1d69c8c21dba4b171a1206d8ee45cbfdbc

Author: craymichael

captum/attr/_utils/interpretable_input.py

@@ -286,6 +286,8 @@ def __init__(
         self.n_features = n_features
         self.n_itp_features = n_itp_features
 
+        # preserve template before modification
+        self.template = template
         if isinstance(template, str):
             template = template.format
         else: