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https://github.com/ikamensh/flynt
A tool to automatically convert old string literal formatting to f-strings
https://github.com/ikamensh/flynt
linter python
Last synced: about 2 months ago
JSON representation
A tool to automatically convert old string literal formatting to f-strings
- Host: GitHub
- URL: https://github.com/ikamensh/flynt
- Owner: ikamensh
- License: mit
- Created: 2019-03-09T18:26:38.000Z (almost 6 years ago)
- Default Branch: master
- Last Pushed: 2024-08-21T16:11:12.000Z (4 months ago)
- Last Synced: 2024-09-22T17:07:17.281Z (3 months ago)
- Topics: linter, python
- Language: Python
- Homepage:
- Size: 510 KB
- Stars: 683
- Watchers: 14
- Forks: 33
- Open Issues: 25
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
Awesome Lists containing this project
- awesome-python-code-formatters - flynt - strings. (UNIX-way formatters)
README
# flynt - string formatting converter
`flynt` is a command line tool to automatically convert a project's Python code from old "%-formatted" and .format(...) strings into Python 3.6+'s "f-strings".
F-Strings:
> Not only are they more readable, more concise, and less prone to error than other ways of formatting, but they are also faster!
### Installation
`pip install flynt`. It requires Python version 3.7+.
### Usage
*Flynt will modify the files it runs on. Add your project to version control system before using flynt.*
To run: `flynt {source_file_or_directory}`
* Given a single file, it will 'f-stringify' it: replace all applicable string formatting in this file (file will be modified).
* Given a folder, it will search the folder recursively and f-stringify all the .py files it finds. It skips some hard-coded folder names: `blacklist = {'.tox', 'venv', 'site-packages', '.eggs'}`.
It turns the code it runs on into Python 3.6+, since 3.6 is when "f-strings" were introduced.
### Command line options
From the output of `flynt -h`:
```
usage: flynt [-h] [-v | -q] [--no-multiline | -ll LINE_LENGTH]
[-d | --stdout] [-s] [--no-tp] [--no-tf] [-tc] [-tj]
[-f] [-a] [-e EXCLUDE [EXCLUDE ...]] [--version]
[src ...]
flynt v.0.78
positional arguments:
src source file(s) or directory (or a single `-`
to read stdin and output to stdout)
optional arguments:
-h, --help show this help message and exit
-v, --verbose run with verbose output
-q, --quiet run without outputting statistics to stdout
--no-multiline convert only single line expressions
-ll LINE_LENGTH, --line-length LINE_LENGTH
for expressions spanning multiple lines,
convert only if the resulting single line
will fit into the line length limit. Default
value is 88 characters.
-d, --dry-run Do not change the files in-place and print
the diff instead. Note that this must be
used in conjunction with '--fail-on-change'
when used for linting purposes.
--stdout Do not change the files in-place and print
the result instead. This argument implies
--quiet, i.e. no statistics are printed to
stdout, only the resulting code. It is
incompatible with --dry-run and --verbose.
-s, --string Interpret the input as a Python code snippet
and print the converted version. The snippet
must use single quotes or escaped double
quotes.
--no-tp, --no-transform-percent
Don't transform % formatting to f-strings
(default: do so)
--no-tf, --no-transform-format
Don't transform .format formatting to
f-strings (default: do so)
-tc, --transform-concats
Replace string concatenations (defined as +
operations involving string literals) with
f-strings. Available only if flynt is
installed with 3.8+ interpreter.
-tj, --transform-joins
Replace static joins (where the joiner is a
string literal and the joinee is a static-
length list) with f-strings. Available only
if flynt is installed with 3.8+ interpreter.
-f, --fail-on-change Fail when changing files (for linting
purposes)
-a, --aggressive Include conversions with potentially changed
behavior.
-e EXCLUDE [EXCLUDE ...], --exclude EXCLUDE [EXCLUDE ...]
ignore files with given strings in it's
absolute path.
--version Print the current version number and exit.
```
### Sample output of a successful run:
```
38f9d3a65222:~ ikkamens$ git clone https://github.com/pallets/flask.git
Cloning into 'flask'...
...
Resolving deltas: 100% (12203/12203), done.
38f9d3a65222:open_source ikkamens$ flynt flask
Running flynt v.0.40
Flynt run has finished. Stats:
Execution time: 0.789s
Files modified: 21
Character count reduction: 299 (0.06%)
Per expression type:
Old style (`%`) expressions attempted: 40/42 (95.2%)
`.format(...)` calls attempted: 26/33 (78.8%)
F-string expressions created: 48
Out of all attempted transforms, 7 resulted in errors.
To find out specific error messages, use --verbose flag.
_-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_._-_.
Please run your tests before committing. Did flynt get a perfect conversion? give it a star at:
~ https://github.com/ikamensh/flynt ~
Thank you for using flynt. Upgrade more projects and recommend it to your colleagues!
38f9d3a65222:~ ikkamens$
```
### Pre-commit hook
To make sure all formatted strings are always converted to f-strings, you can
add flynt to your [pre-commit](https://www.pre-commit.com) hooks.
Add a new section to `.pre-commit-config.yaml`:
```
- repo: https://github.com/ikamensh/flynt/
rev: ''
hooks:
- id: flynt
```
This will run flynt on all modified files before committing.
You can skip conversion of certain lines by adding `# noqa [: anything else] flynt [anything else]`
### Configuration files
Since v0.71 flynt can be configured using `pyproject.toml` file on a per-project basis.
Use same arguments as in CLI, and add them to `[tool.flynt]` section. CLI arguments takes precedence over the config file.
It can also be configured globally with a toml file located in `~/.config/flynt.toml` on Unix / `~/.flynt.toml` on Windows.
### About
Read up on f-strings here:
- https://realpython.com/python-f-strings/
- https://www.python.org/dev/peps/pep-0498/
After obsessively refactoring a project at work, and not even covering 50% of f-string candidates, I realized there was some place for automation. Also it was very interesting to work with ast module.
### Dangers of conversion
It is not guaranteed that formatted strings will be exactly the same as before conversion.
`'%s' % var` is converted to `f'{var}'`. There is a case when this will behave different from the original - if var is a tuple of one element. In this case, %s displays the element, and f-string displays the tuple. Example:
```
foo = (1,)
print('%s' % foo) # prints '1'
print(f'{foo}') # prints '(1,)'
```
Furthermore, some arguments cause formatting of strings to throw exceptions. One example where f-strings are inconsistent with previous formatting is %d vs {:d} - new format no longer accepts floats. While most cases are covered by taking the formatting specifiers to the f-strings format, the precise exception behaviour might differ as well. Make sure you have sufficient test coverage.
### Other Credits / Dependencies / Links
- [astor](https://github.com/berkerpeksag/astor) is used to turn the transformed AST back into code.
- Thanks to folks from [pyddf](https://www.pyddf.de/) for their support, advice and participation during spring hackathon 2019, in particular Holger Hass, Farid Muradov, Charlie Clark.
- Logic finding the pyproject.toml and parsing it was partially copied from [black](https://github.com/psf/black)