Viz_classes code cleanup (#1073)

Some very minor cleanup of some code in viz_classes. Changes include:

1. Using raw strings to properly escape regex tokens. This silences some
warnings.
2. Properly close the sql files that are opened
3. Use native set difference instead of manually computing it with a
list comprehension.

Core/LAMBDA/layers/viz_lambda_shared_funcs/python/viz_classes.py

@@ -4,6 +4,7 @@
 import re
 import urllib.parse
 import inspect
+import pathlib
 try:
     import fsspec
 except:
@@ -98,7 +99,7 @@ def load_df_into_db(self, table_name, df, drop_first=True):
     ###################################
     def execute_sql(self, sql):
         if sql.endswith('.sql') and os.path.exists(sql):
-            sql = open(sql, 'r').read()
+            sql = pathlib.Path(sql).read_text()
         with self.connection:
             try:
                 with self.connection.cursor() as cur:
@@ -111,7 +112,7 @@ def execute_sql(self, sql):
     ###################################                
     def sql_to_dataframe(self, sql, return_geodataframe=False):
         if sql.endswith(".sql"):
-            sql = open(sql, 'r').read()
+            sql = pathlib.Path(sql).read_text()
 
         db_engine = self.engine
         if not return_geodataframe:
@@ -223,16 +224,16 @@ def check_required_tables_updated(self, sql_path_or_str, sql_replace={}, referen
         issues_encountered = []
         # Determine if arg is file or raw SQL string
         if os.path.exists(sql_path_or_str):
-            sql = open(sql_path_or_str, 'r').read()
+            sql = pathlib.Path(sql_path_or_str).read_text()
         else:
             sql = sql_path_or_str
 
         for word, replacement in sql_replace.items():
             sql = re.sub(word, replacement, sql, flags=re.IGNORECASE).replace('utc', 'UTC')
 
-        output_tables = set(re.findall('(?<=INTO )\w+\.\w+', sql, flags=re.IGNORECASE)) 
-        input_tables = set(re.findall('(?<=FROM |JOIN )\w+\.\w+', sql, flags=re.IGNORECASE))
-        check_tables = [t for t in input_tables if t not in output_tables]
+        output_tables = set(re.findall(r'(?<=INTO\s)\w+\.\w+', sql, flags=re.IGNORECASE)) 
+        input_tables = set(re.findall(r'(?<=FROM\s|JOIN\s)\w+\.\w+', sql, flags=re.IGNORECASE))
+        check_tables = input_tables - output_tables
 
         if not check_tables:
             return True