diff --git a/asdl/arith_ast_test.py b/asdl/arith_ast_test.py
index 9642690184..1537eafcdb 100755
--- a/asdl/arith_ast_test.py
+++ b/asdl/arith_ast_test.py
@@ -6,7 +6,6 @@
 import cStringIO
 import unittest
 
-from asdl import format as fmt
 from asdl import py_meta
 from asdl import asdl_
 from asdl import const
diff --git a/asdl/arith_parse.py b/asdl/arith_parse.py
index f707d74bc1..5eacd68e45 100755
--- a/asdl/arith_parse.py
+++ b/asdl/arith_parse.py
@@ -7,7 +7,7 @@
 import sys
 
 from asdl import tdop
-from asdl.tdop import Node, CompositeNode
+from asdl.tdop import CompositeNode
 from asdl import arith_ast
 
 op_id = arith_ast.op_id_e  # TODO: Rename this back.
diff --git a/asdl/asdl_demo.py b/asdl/asdl_demo.py
index c4fded9317..74f34071a3 100755
--- a/asdl/asdl_demo.py
+++ b/asdl/asdl_demo.py
@@ -12,7 +12,9 @@
 from asdl import format as fmt
 
 from core.id_kind import Id
-from core.util import log
+from core import util
+
+log = util.log
 
 
 def main(argv):
@@ -41,7 +43,7 @@ def main(argv):
     # demo.
     py_meta.MakeTypes(module, root, type_lookup)
 
-    print('Dynamically created a Python module with these types:')
+    log('Dynamically created a Python module with these types:')
     for name in dir(root):
       print('\t' + name)
 
diff --git a/asdl/encode.py b/asdl/encode.py
index fbad0d2f56..eaab2192e3 100644
--- a/asdl/encode.py
+++ b/asdl/encode.py
@@ -2,8 +2,6 @@
 encode.py
 """
 
-import sys
-
 from asdl import asdl_ as asdl
 from asdl import py_meta
 from asdl import const
diff --git a/asdl/format.py b/asdl/format.py
index 309c7f83b6..78e323ec29 100644
--- a/asdl/format.py
+++ b/asdl/format.py
@@ -16,7 +16,6 @@
 """
 
 import re
-import sys
 
 from asdl import asdl_ as asdl
 from core import util
diff --git a/asdl/format_test.py b/asdl/format_test.py
index e8757ce7f5..c0ce9f1007 100755
--- a/asdl/format_test.py
+++ b/asdl/format_test.py
@@ -4,12 +4,9 @@
 """
 
 import cStringIO
-import sys
 import unittest
 
-
 from asdl import format as fmt
-from asdl import asdl_
 
 from asdl import arith_ast  # module under test
 
diff --git a/asdl/gen_cpp.py b/asdl/gen_cpp.py
index ec9d86edb9..0e1686c63f 100755
--- a/asdl/gen_cpp.py
+++ b/asdl/gen_cpp.py
@@ -28,7 +28,6 @@
 import sys
 
 from asdl import asdl_ as asdl
-from asdl import py_meta
 from asdl import encode
 
 TABSIZE = 2
diff --git a/asdl/py_meta.py b/asdl/py_meta.py
index 0dc4a63938..d75a448c08 100755
--- a/asdl/py_meta.py
+++ b/asdl/py_meta.py
@@ -26,13 +26,13 @@
 put: an op is Add() and not Add, an instance of a class, not an integer value.
 """
 
-import sys
-
 from asdl import asdl_ as asdl
 from asdl import const
 from asdl import format as fmt
 from core import util
 
+log = util.log
+
 
 def _CheckType(value, expected_desc):
   """Is value of type expected_desc?
@@ -86,12 +86,8 @@ def _CheckType(value, expected_desc):
     if asdl.is_simple(expected_desc):
       return actual_desc is expected_desc
     else:
-      for cons in expected_desc.types:
-        #print("CHECKING desc %s against %s" % (desc, cons))
-
-        # It has to be one of the alternatives
-        from core.util import log
-        #log('Checking %s against %s', actual_desc, cons)
+      for cons in expected_desc.types:  # It has to be one of the alternatives
+        #log("CHECKING desc %s against %s" % (desc, cons))
         if actual_desc is cons:
           return True
       return False
diff --git a/asdl/py_meta_test.py b/asdl/py_meta_test.py
index 372840ea13..f6f6e7795e 100755
--- a/asdl/py_meta_test.py
+++ b/asdl/py_meta_test.py
@@ -3,13 +3,14 @@
 py_meta_test.py: Tests for py_meta.py
 """
 
-import re
 import unittest
 
 from asdl import py_meta  # module under test
 
 class AsdlTest(unittest.TestCase):
-  pass
+
+  def testPyMeta(self):
+    print py_meta
 
 
 if __name__ == '__main__':
diff --git a/bin/oil.py b/bin/oil.py
index a533c6ef28..3b4f61c7d4 100755
--- a/bin/oil.py
+++ b/bin/oil.py
@@ -51,7 +51,6 @@ def _tlog(msg):
 
 import errno
 import platform
-import re
 #import traceback  # for debugging
 
 # Set in Modules/main.c.
diff --git a/core/builtin.py b/core/builtin.py
index 1e173ab91a..a7c0aaaa79 100755
--- a/core/builtin.py
+++ b/core/builtin.py
@@ -30,13 +30,11 @@
 import sys
 
 from core import args
-from core import legacy
 from core import lexer
 from core import runtime
 from core import util
 from core import state
 from core import word_compile
-from core.id_kind import Id
 
 from osh import lex
 
diff --git a/core/builtin_test.py b/core/builtin_test.py
index ac38709387..53c66a96b9 100755
--- a/core/builtin_test.py
+++ b/core/builtin_test.py
@@ -6,7 +6,6 @@
 import unittest
 
 from core import legacy
-from core import lexer
 from core import builtin  # module under test
 
 
diff --git a/core/cmd_exec.py b/core/cmd_exec.py
index 408c7ebf51..580ba0442b 100755
--- a/core/cmd_exec.py
+++ b/core/cmd_exec.py
@@ -17,7 +17,6 @@
 
 import os
 import resource
-import stat
 import sys
 import time
 
@@ -1007,7 +1006,6 @@ def _Dispatch(self, node, fork_external):
           if not b:
             break
 
-          do_continue = False
           try:
             status = self._Execute(node.body)
           except _ControlFlow as e:
diff --git a/core/cmd_exec_test.py b/core/cmd_exec_test.py
index 15812a706b..8acf9e8c9d 100755
--- a/core/cmd_exec_test.py
+++ b/core/cmd_exec_test.py
@@ -9,19 +9,15 @@
 cmd_exec_test.py: Tests for cmd_exec.py
 """
 
-import os
 import unittest
 
-from core import alloc
 from core import builtin
 from core import cmd_exec  # module under test
 from core.cmd_exec import *
 from core.id_kind import Id
 from core import completion
 from core import legacy
-from core import ui
 from core import word_eval
-from core import runtime
 from core import process
 from core import test_lib
 
diff --git a/core/completion.py b/core/completion.py
index cc7aefb40c..bc66d1e4b8 100755
--- a/core/completion.py
+++ b/core/completion.py
@@ -33,7 +33,6 @@
 import fnmatch
 import readline
 import os
-import stat
 import sys
 import time
 import traceback
@@ -45,7 +44,6 @@
 from core import state
 from core import ui
 from core import util
-from core.id_kind import Id
 
 command_e = ast.command_e
 value_e = runtime.value_e
@@ -786,7 +784,6 @@ def Init(pool, builtins, mem, funcs, comp_lookup, status_out, ev):
 
 if __name__ == '__main__':
   from core import builtin
-  from core import cmd_exec
   from core import state
 
   status_lines = ui.MakeStatusLines()
diff --git a/core/completion_test.py b/core/completion_test.py
index dfcef35fb3..f4fb6f9ee6 100755
--- a/core/completion_test.py
+++ b/core/completion_test.py
@@ -12,11 +12,9 @@
 import unittest
 
 from core import alloc
-from core import cmd_exec
 from core import cmd_exec_test
 from core import completion  # module under test
 from core import legacy
-from core import lexer
 from core import state
 from core import test_lib
 from core import word_eval
diff --git a/core/glob_.py b/core/glob_.py
index 8d038f369a..02b0ca3595 100644
--- a/core/glob_.py
+++ b/core/glob_.py
@@ -10,7 +10,8 @@
 except ImportError:
   from benchmarks import fake_libc as libc
 
-from core.util import log
+from core import util
+log = util.log
 
 
 def LooksLikeGlob(s):
diff --git a/core/lexer.py b/core/lexer.py
index 93f1f11fce..0b5d8b4cae 100644
--- a/core/lexer.py
+++ b/core/lexer.py
@@ -16,7 +16,7 @@
 from core.id_kind import Id
 from osh import ast_ as ast
 
-from core.util import log
+log = util.log
 
 
 def C(pat, tok_type):
diff --git a/core/lexer_gen_test.py b/core/lexer_gen_test.py
index 7c9d513c33..7bf4904a8a 100755
--- a/core/lexer_gen_test.py
+++ b/core/lexer_gen_test.py
@@ -1,11 +1,10 @@
 #!/usr/bin/python -S
 """
-lex_gen_test.py: Tests for lex_gen.py
+lexer_gen_test.py: Tests for lexer_gen.py
 """
 
 import unittest
 
-from osh import lex
 from core import lexer_gen  # module under test
 
 
diff --git a/core/libstr_test.py b/core/libstr_test.py
index 3504ffc2e4..0503e5dc66 100755
--- a/core/libstr_test.py
+++ b/core/libstr_test.py
@@ -11,6 +11,8 @@
 class LibStrTest(unittest.TestCase):
 
   def testUnarySuffixOpDemo(self):
+    print libstr
+
     s = 'abcd'
     n = len(s)
 
diff --git a/core/process.py b/core/process.py
index b8d71a5d95..2fc0dbbf23 100644
--- a/core/process.py
+++ b/core/process.py
@@ -18,7 +18,7 @@
 
 from core import runtime
 from core import util
-from core.id_kind import Id, REDIR_DEFAULT_FD
+from core.id_kind import Id
 
 redirect_e = runtime.redirect_e
 e_die = util.e_die
diff --git a/core/process_test.py b/core/process_test.py
index 1d31710531..a4ab29b55a 100755
--- a/core/process_test.py
+++ b/core/process_test.py
@@ -4,7 +4,6 @@
 """
 
 import os
-import sys
 import unittest
 
 from core.id_kind import Id
@@ -49,12 +48,10 @@ def testStdinRedirect(self):
 
     r = runtime.PathRedirect(Id.Redir_Less, 0, PATH)
     fd_state.Push([r], waiter)
-    #line1 = sys.stdin.readline()
     line1 = builtin.ReadLineFromStdin()
     fd_state.Pop()
 
     fd_state.Push([r], waiter)
-    #line2 = sys.stdin.readline()
     line2 = builtin.ReadLineFromStdin()
     fd_state.Pop()
 
diff --git a/core/reader.py b/core/reader.py
index 913b34c567..c82614fb2b 100644
--- a/core/reader.py
+++ b/core/reader.py
@@ -12,6 +12,7 @@
 import cStringIO
 
 from core import util
+log = util.log
 
 
 class _Reader(object):
diff --git a/core/test_builtin.py b/core/test_builtin.py
index 63a4f64548..66e29e7681 100644
--- a/core/test_builtin.py
+++ b/core/test_builtin.py
@@ -8,7 +8,6 @@
 
 from core import id_kind
 from core import expr_eval
-from core import word
 from core import runtime
 from core import util
 
diff --git a/core/word.py b/core/word.py
index 8e2ded1d2e..19d1f78c36 100644
--- a/core/word.py
+++ b/core/word.py
@@ -2,7 +2,6 @@
 word.py -- Functions for using words as "tokens".
 """
 
-import sys
 from osh import ast_ as ast
 from core.id_kind import Id, Kind, LookupKind
 from core import util
diff --git a/core/word_eval.py b/core/word_eval.py
index beba54f9d1..f5871d7a19 100644
--- a/core/word_eval.py
+++ b/core/word_eval.py
@@ -7,7 +7,6 @@
 
 from core import braces
 from core import expr_eval
-from core import legacy
 from core import libstr
 from core import glob_
 from core.id_kind import Id, Kind, LookupKind
diff --git a/core/word_eval_test.py b/core/word_eval_test.py
index ca344b419b..5402f55f0d 100755
--- a/core/word_eval_test.py
+++ b/core/word_eval_test.py
@@ -15,7 +15,9 @@
 
 
 class WordEvalTest(unittest.TestCase):
-  pass
+
+  def testWordEval(self):
+    print word_eval
 
 
 if __name__ == '__main__':
diff --git a/core/word_test.py b/core/word_test.py
index 45b60294a7..31d06b92a5 100755
--- a/core/word_test.py
+++ b/core/word_test.py
@@ -11,7 +11,7 @@
 class WordTest(unittest.TestCase):
 
   def testFoo(self):
-    print('Hello from word_test.py')
+    print word
 
 
 if __name__ == '__main__':
diff --git a/osh/arith_parse.py b/osh/arith_parse.py
index 5344b251fe..0d0fd1a606 100755
--- a/osh/arith_parse.py
+++ b/osh/arith_parse.py
@@ -3,8 +3,6 @@
 arith_parse.py - Parse shell arithmetic, which is based on C.
 """
 
-import sys
-
 from core import tdop
 from core import util
 from core.id_kind import Id
diff --git a/osh/arith_parse_test.py b/osh/arith_parse_test.py
index fe25e2af0a..9e6c05a045 100755
--- a/osh/arith_parse_test.py
+++ b/osh/arith_parse_test.py
@@ -13,9 +13,7 @@
 
 from core import expr_eval
 from core import legacy
-from core import tdop
 from core import word_eval
-from core import cmd_exec
 from core import state
 from core import test_lib
 
@@ -30,9 +28,6 @@ class ExprSyntaxError(Exception):
 def ParseAndEval(code_str):
   arena = test_lib.MakeArena('<arith_parse_test.py>')
   w_parser, _ = parse_lib.MakeParserForCompletion(code_str, arena)
-  #spec = arith_parse.MakeShellSpec()
-  #a_parser = tdop.TdopParser(spec, w_parser)  # Calls ReadWord(lex_mode_e.ARITH)
-  #anode = a_parser.Parse()
   anode = w_parser._ReadArithExpr()  # need the right lex state?
 
   if not anode:
diff --git a/osh/ast_gen.py b/osh/ast_gen.py
index 7e4cf9f747..32702bcf3f 100755
--- a/osh/ast_gen.py
+++ b/osh/ast_gen.py
@@ -5,7 +5,6 @@
 
 import sys
 
-from core import util
 from osh import ast_ as ast
 from asdl import gen_cpp
 
diff --git a/osh/bool_parse.py b/osh/bool_parse.py
index 77a848cc64..5bfa6d939c 100755
--- a/osh/bool_parse.py
+++ b/osh/bool_parse.py
@@ -32,8 +32,6 @@
 BINARY_OP: -gt, -ot, ==, etc.
 """
 
-import sys
-
 from osh import ast_ as ast
 
 from core import word
diff --git a/osh/cmd_parse.py b/osh/cmd_parse.py
index 863a7564bf..c5c90e3f36 100644
--- a/osh/cmd_parse.py
+++ b/osh/cmd_parse.py
@@ -10,8 +10,6 @@
 cmd_parse.py - Parse high level shell commands.
 """
 
-import sys
-
 from asdl import const
 
 from core import braces
diff --git a/osh/cmd_parse_test.py b/osh/cmd_parse_test.py
index 60ff0ade36..10df708ea9 100755
--- a/osh/cmd_parse_test.py
+++ b/osh/cmd_parse_test.py
@@ -6,11 +6,8 @@
 import sys
 import unittest
 
-from asdl import py_meta
-
 from core import ui
 from core.id_kind import Id
-from core.alloc import Pool
 from core import word
 from core import test_lib
 
diff --git a/osh/lex.py b/osh/lex.py
index 1e98321e3a..291074eb9d 100644
--- a/osh/lex.py
+++ b/osh/lex.py
@@ -103,10 +103,10 @@
 import re
 
 from core.id_kind import Id, Kind, ID_SPEC
-from core import util
 from core.lexer import C, R
 
 from osh import ast_ as ast
+
 lex_mode_e = ast.lex_mode_e
 
 
diff --git a/osh/lex_test.py b/osh/lex_test.py
index 5cfa3ce87d..05a44a4da0 100755
--- a/osh/lex_test.py
+++ b/osh/lex_test.py
@@ -5,9 +5,8 @@
 
 import unittest
 
-from core import alloc
 from core.id_kind import Id, Kind, LookupKind
-from core.lexer import CompileAll, Lexer, LineLexer
+from core.lexer import CompileAll, LineLexer
 from core import test_lib
 
 from osh import parse_lib
diff --git a/osh/parse_lib.py b/osh/parse_lib.py
index 6b6d8a9ffe..f6a80db1e5 100644
--- a/osh/parse_lib.py
+++ b/osh/parse_lib.py
@@ -2,8 +2,6 @@
 parse_lib.py - Consolidate various parser instantiations here.
 """
 
-import sys
-
 from core import lexer
 from core import reader
 from core import id_kind
diff --git a/osh/word_parse.py b/osh/word_parse.py
index 6894a23765..e8ae7be043 100644
--- a/osh/word_parse.py
+++ b/osh/word_parse.py
@@ -429,9 +429,7 @@ def _ReadBracedBracedVarSub(self, d_quoted=False):
     self._Next(lex_mode_e.VS_1)
     self._Peek()
 
-    debug_token = self.cur_token
     ty = self.token_type
-    #print("T", debug_token)
 
     if ty == Id.VSub_Pound:
       # Disambiguate
diff --git a/osh/word_parse_test.py b/osh/word_parse_test.py
index 9230a198ed..dd8ba85e1b 100755
--- a/osh/word_parse_test.py
+++ b/osh/word_parse_test.py
@@ -15,8 +15,8 @@
 
 from core import alloc
 from core.id_kind import Id
-from core import word
 from core import test_lib
+from core import word
 
 from osh import ast_ as ast
 from osh import parse_lib
@@ -491,8 +491,6 @@ def testMultiLine(self):
     test_lib.AssertAsdlEqual(self, ast.TokenWord(t), w)
 
   def testParseErrorLocation(self):
-    from core import word
-
     w = _assertSpanForWord(self, 'a=(1 2 3)')
 
     w = _assertSpanForWord(self, 'foo')
diff --git a/test/lint.sh b/test/lint.sh
index 87514bbd6d..2953a00b95 100755
--- a/test/lint.sh
+++ b/test/lint.sh
@@ -99,12 +99,19 @@ bin-flake8() {
 
 flake8-all() {
   local -a dirs=(asdl bin core osh)
-  # stop the build if there are Python syntax errors or undefined names
+
+  # Step 1: Stop the build if there are Python syntax errors or undefined names
   bin-flake8 "${dirs[@]}" \
-    --count --select=E901,E999,F821,F822,F823 --show-source --statistics
+    --count --select=E901,E999,F821,F822,F823,F401 --show-source --statistics
+
+  # Step 2: Style errors as warnings.
+  local ignored='E125,E701,E241,E121,E111,E114,E128,E262,E226,E302,E265,E290,E202,E203,C901'
+  # trailing whitespace, line too long, blank lines
+  local ignored_for_now='W291,E501,E303'
 
   # exit-zero treats all errors as warnings.  The GitHub editor is 127 chars wide
   bin-flake8 "${dirs[@]}" \
+    --ignore="$ignored,$ignored_for_now" \
     --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
 }