Add conversion to f-strings using flynt

.github/workflows/help-in-readme.yml

@@ -6,7 +6,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
-      - run: pip install '.[isort]'
+      - run: pip install '.[flynt,isort]'
       - name: Verify that README contains output of darker --help
         shell: python
         run: |

.github/workflows/mypy.yml

@@ -13,6 +13,7 @@ jobs:
       - run: |
           pip install -U \
             black \
+            flynt \
             isort \
             mypy>=0.990 \
             pytest \

CHANGES.rst

@@ -5,6 +5,8 @@ These features will be included in the next release:
 
 Added
 -----
+- ``-f`` / ``--flynt`` option for converting old-style format strings to f-strings as
+  supported in Python 3.6+.
 - Make unit tests compatible with ``pytest --log-cli-level==DEBUG``.
   Doctests are still incompatible due to
   `pytest#5908 <https://github.com/pytest-dev/pytest/issues/5908>`_.

README.rst

@@ -43,6 +43,7 @@ The reformatters supported are:
 
 - Black_ for code reformatting
 - isort_ for sorting imports
+- flynt_ for turning old-style format strings to f-strings
 
 See `Using linters`_ below for the list of supported linters.
 
@@ -53,6 +54,7 @@ see the relevant sections below in this document.
 
 .. _Black: https://github.com/python/black
 .. _isort: https://github.com/timothycrosley/isort
+.. _flynt: https://github.com/ikamensh/flynt
 .. _Pytest: https://docs.pytest.org/
 .. _pytest-darker: https://pypi.org/project/pytest-darker/
 
@@ -164,10 +166,13 @@ You can enable additional features with command line options:
 - ``-i`` / ``--isort``: Reorder imports using isort_. Note that isort_ must be
   run in the same Python environment as the packages to process, as it imports
   your modules to determine whether they are first or third party modules.
+- ``-f`` / ``--flynt``: Also convert string formatting to use f-strings using the
+  ``flynt`` package
 - ``-L <linter>`` / ``--lint <linter>``: Run a supported linter (see `Using linters`_)
 
 *New in version 1.1.0:* The ``-L`` / ``--lint`` option.
 *New in version 1.2.2:* Package available in conda-forge_.
+*New in version 1.7.0:* The ``-f`` / ``--flynt`` option
 
 .. _Conda: https://conda.io/
 .. _conda-forge: https://conda-forge.org/
@@ -314,6 +319,8 @@ The following `command line arguments`_ can also be used to modify the defaults:
 --check
        Don't write the files back, just return the status. Return code 0 means nothing
        would change. Return code 1 means some files would be reformatted.
+-f, --flynt
+       Also convert string formatting to use f-strings using the ``flynt`` package
 -i, --isort
        Also sort imports using the ``isort`` package
 -L CMD, --lint CMD
@@ -365,6 +372,7 @@ project's root directory, or to a different TOML file specified using the ``-c``
    diff = true
    check = true
    isort = true
+   flynt = true
    lint = [
        "pylint",
    ]
@@ -421,6 +429,8 @@ command line options
 
 *New in version 1.7.0:* The ``-t`` / ``--target-version`` command line option
 
+*New in version 1.7.0:* The ``-f`` / ``--flynt`` command line option
+
 .. _Black documentation about pyproject.toml: https://black.readthedocs.io/en/stable/usage_and_configuration/the_basics.html#configuration-via-a-file
 .. _isort documentation about config files: https://timothycrosley.github.io/isort/docs/configuration/config_files/
 .. _public GitHub repositories which install and run Darker: https://github.com/search?q=%2Fpip+install+.*darker%2F+path%3A%2F%5E.github%5C%2Fworkflows%5C%2F.*%2F&type=code

constraints-oldest.txt

@@ -9,6 +9,7 @@ defusedxml==0.7.1
 flake8-2020==1.6.1
 flake8-bugbear==22.1.11
 flake8-comprehensions==3.7.0
+flynt==0.76
 Pygments==2.4.0
 pytest==6.2.0
 pytest-kwparametrize==0.0.3

mypy.ini

@@ -78,6 +78,9 @@ warn_return_any = False
 [mypy-defusedxml.*]
 ignore_missing_imports = True
 
+[mypy-flynt.*]
+ignore_missing_imports = True
+
 [mypy-isort.*]
 ignore_missing_imports = True
 

setup.cfg

@@ -45,6 +45,8 @@ pygments.lexers =
     lint_description = darker.highlighting.lexers:DescriptionLexer
 
 [options.extras_require]
+flynt =
+    flynt>=0.76
 isort =
     isort>=5.0.1
 color =
@@ -55,6 +57,7 @@ test =
     black>=21.7b1  # to prevent Mypy error about `gen_python_files`, see issue #189
     cryptography>=3.3.2  # through twine, fixes CVE-2020-36242
     defusedxml>=0.7.1
+    flynt>=0.76
     isort>=5.0.1
     pygments
     pytest>=6.2.0