Update excel_to_base64 to always close file handles

Author: jlubken

src/penn_chime/utils.py

@@ -6,7 +6,7 @@
 
 
 def dataframe_to_base64(df: pd.DataFrame) -> str:
-    """Converts a dataframe to a base64-encoded CSV representation of that data.
+    """Converts a dataframe into csv base64-encoded data.
 
     This is useful for building datauris for use to download the data in the browser.
 
@@ -18,7 +18,7 @@ def dataframe_to_base64(df: pd.DataFrame) -> str:
     return b64
 
 
-def excel_to_base64(str_excel_filename) -> str:
-    data = open(str_excel_filename, 'rb').read()
-    b64 = b64encode(data).decode()
-    return b64
+def excel_to_base64(filename: str) -> str:
+    """Converts an excel document into base64-encoded data."""
+    with open(filename, 'rb') as fin:
+        return b64encode(fin.read()).decode()