fix linting errors

src/pip/_internal/cli/cmdoptions.py

@@ -403,12 +403,14 @@ def handle_cli_no_binary(option, opt_str, value, parser):
         value, existing.no_binary, existing.only_binary,
     )
 
+
 def handle_cli_only_binary(option, opt_str, value, parser):
     existing = getattr(parser.values, option.dest)
     FormatControl.handle_mutual_excludes(
         value, existing.only_binary, existing.no_binary,
     )
 
+
 def no_binary():
     format_control = FormatControl(set(), set())
     return Option(

src/pip/_internal/commands/download.py

@@ -5,8 +5,6 @@ import os
 
 from pip._internal.cli import cmdoptions
 from pip._internal.cli.base_command import RequirementCommand
-from pip._internal.exceptions import CommandError
-from pip._internal.format_control import FormatControl
 from pip._internal.operations.prepare import RequirementPreparer
 from pip._internal.req import RequirementSet
 from pip._internal.req.req_tracker import RequirementTracker

tests/unit/test_format_control.py

@@ -57,6 +57,7 @@ def test_comma_separated_values():
     assert cmd.options.format_control.only_binary == expected.only_binary
     assert cmd.options.format_control.no_binary == expected.no_binary
 
+
 def test_fmt_ctl_matches():
     fmt = FormatControl(set(), set())
     assert fmt.get_allowed_formats("fred") == frozenset(["source", "binary"])