[STYLE] check python with flake8 (#424)

I've been using this locally to find errors without running tests, and now that we're using autopep8, it passes with minimal suppressions. This is also what turned up the issues with the tutorials, which were fixed in #422.

python/triton/code_gen.py

@@ -1,19 +1,17 @@
 import ast
 import builtins
-import dbm
 import functools
 import hashlib
 import inspect
 import os
 import pickle
-import struct
 import subprocess
 import sys
 import tempfile
 import textwrap
 import time
 import warnings
-from typing import Dict, Optional
+from typing import Dict
 
 import torch
 from filelock import FileLock
@@ -406,7 +404,7 @@ class CodeGenerator(ast.NodeVisitor):
                                                    self.visit(pos_cond_node),
                                                    self.visit(neg_cond_node),
                                                    _builder=self.builder)
-        #cond_node = neg_cond_node
+        # cond_node = neg_cond_node
         step_node = ast.AugAssign(target=st_target, op=ast.Add(), value=arg_2)
         # code generation
         current_bb = self.builder.get_insert_block()