Re-enable pyflakes in linter and remove python 3 pyflakes errors.

provision.py

@@ -122,7 +122,7 @@ def setup_virtualenv(target_venv_path, requirements_file, virtualenv_args=[]):
     print("Using cached Python venv from %s" % (cached_venv_path,))
     run(["sudo", "ln", "-nsf", cached_venv_path, target_venv_path])
     activate_this = os.path.join(target_venv_path, "bin", "activate_this.py")
-    execfile(activate_this, dict(__file__=activate_this))
+    exec(open(activate_this).read(), {}, dict(__file__=activate_this)) # type: ignore # https://github.com/python/mypy/issues/1577
 
 def do_setup_virtualenv(venv_path, requirements_file, virtualenv_args):
     # Setup Python virtualenv
@@ -133,7 +133,7 @@ def do_setup_virtualenv(venv_path, requirements_file, virtualenv_args):
 
     # Switch current Python context to the virtualenv.
     activate_this = os.path.join(venv_path, "bin", "activate_this.py")
-    execfile(activate_this, dict(__file__=activate_this))
+    exec(open(activate_this).read(), {}, dict(__file__=activate_this)) # type: ignore # https://github.com/python/mypy/issues/1577
 
     run(["pip", "install", "--upgrade", "pip"])
     run(["pip", "install", "--no-deps", "--requirement", requirements_file])

tools/emoji_dump/emoji_dump.py

@@ -5,6 +5,7 @@ import shutil
 import subprocess
 import json
 import sys
+from six import unichr
 
 from PIL import Image, ImageDraw, ImageFont
 

tools/lint-all

@@ -60,7 +60,6 @@ else:
     logger.setLevel(logging.WARNING)
 
 def check_pyflakes():
-    return False
     if not by_lang['py']:
         return False
     failed = False

zerver/lib/actions.py

@@ -34,6 +34,7 @@ import six
 from six.moves import filter
 from six.moves import map
 from six.moves import range
+from six import unichr
 
 session_engine = import_module(settings.SESSION_ENGINE)