flake8-use-fstring
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flake8-use-fstring
Jump-start into modern Python by forcing yourself to use f-strings.
Works only with python>=3.6
since it was when f-strings were introduced.
Installation
pip install flake8-use-fstring
Reported Errors
-
FS001
:%
formatting is used. -
FS002
:.format
formatting is used. -
FS003
: f-string missing prefix (ignored by default).
Available Configurations
--percent-greedy
and --format-greedy
This plugin checks each python statement (logical line)
and see if %
or .format
is used.
Since flake8 is only a code style checker and not a type checker,
it's impossible to tell for sure if the value before %
or .format
is a string.
Thus, greedy level is introduced to control when the plugin should report errors.
-
Level 0 (default): only report error if the value before
%
or.format
is a string literal. -
Level 1: report error if a string literal appears before
%
or.format
anywhere in the statement. -
Level 2: report any usage of
%
or.format
.
If the value immediately before %
or .format
is not a string,
using level 1 or 2 may result in false positives.
See tests/example.py for examples.
Thus level 0 is the default level.
However, for most projects it should be reasonable to use greedy level 2 with confidence.
To set greedy levels,
set --percent-greedy=<level>
and --format-greedy=<level>
in the command line,
or set percent-greedy=<level>
and format-greedy=<level>
in the .flake8
config file.
--enable-extensions=FS003
and --fstring-ignore-format
This plugin can also check for strings that appear to be f-strings but don't have the f
prefix.
FS003
will be reported if a string:
- is not prefixed with
f
- contains at least one pair of
{}
- is not prefixed with
r
(because r-strings are often regexes that would contain{}
)
Due to the potential for false positives, this check (FS003
) is disabled by default.
To enable this check,
add the --enable-extensions=FS003
command line option,
or set enable-extensions=FS003
in the .flake8
config file.
NOTE:
If you use the --ignore
option of flake8
, the default ignore list will be overwritten.
See --ignore
vs --extend-ignore
.
The missing prefix check normally ignores strings that are using %
or .format
formatting.
To check those strings as well,
add the --fstring-ignore-format
command line option,
or set fstring-ignore-format=True
in the .flake8
config file.
Additional Notes
Byte literals
Byte literals (strings that are prefixed with a literal b
) will not be checked since Python does not support f-strings for them (as of 3.9).