style: Use f-strings wherever possible

[DimitriPapadopoulos]

They're faster.

[adrienverge]

Looks good, thanks for taking the time!

Have you changed them one by one and checked they all make sense? Or did you use a script to find and replace them? (in some rare cases like %02d, %.2f or %-10s, f-string cannot be used as is)

[coveralls]

coverage: 99.391% (-0.002%) from 99.393% when pulling cb7e19a on DimitriPapadopoulos:f-strings into 816d575 on adrienverge:master.

[DimitriPapadopoulos]

Have you changed them one by one and checked they all make sense? Or did you use a script to find and replace them? (in some rare cases like %02d, %.2f or %-10s, f-string cannot be used as is)

There are not such cases as far as I can see. Yet, it possible to write f{variable!02d}f{variable:02d} or f{variable!.2f}f{variable:.2f}, isn't it?

[adrienverge]

There are not such cases as far as I can see. Yet, it possible to write f{variable!02d} or f{variable!.2f}, isn't it?

Sure it is! I just wanted to make sure you (or your custom script?) looked for them, if any :)

I still see a few %s and %d in some files (namely yamllint/linter.py, yamllint/rules/line_length.py, yamllint/rules/indentation.py and yamllint/rules/octal_values.py). Could you check them?

[DimitriPapadopoulos]

As for the tool I use, it's pyupgrade. But I often end up applying changes manually, because:

1. You cannot limit pyupgrade to a single class of changes. I prefer an individual commit per class of changes.
2. It's not perfect: it often leaves behind some cases of % string interpolation.

[DimitriPapadopoulos]

I have left an instance of % string interpolation in yamllint/rules/line_length.py because I find the f-string interpolation is less readable – unless of course I use additional variables to store the result of complex expressions.

[adrienverge]

I have left an instance of % string interpolation in yamllint/rules/line_length.py

I had spotted this one too and I agree it's better readable like this 👍

I allowed myself to force-push to your branch with a slight rework of modified strings:

--- a/yamllint/config.py
+++ b/yamllint/config.py
@@ -179,8 +179,8 @@ def validate_rule_conf(rule, conf):
                 continue
             if optkey not in options:
                 raise YamlLintConfigError(
-                    f'invalid config: unknown option "{optkey}" '
-                    f'for rule "{rule.ID}"')
+                    f'invalid config: unknown option "{optkey}" for rule '
+                    f'"{rule.ID}"')
             # Example: CONF = {option: (bool, 'mixed')}
             #          → {option: true}         → {option: mixed}
             if isinstance(options[optkey], tuple):
@@ -216,8 +216,8 @@ def validate_rule_conf(rule, conf):
                 raise YamlLintConfigError(f'invalid config: {rule.ID}: {res}')
     else:
         raise YamlLintConfigError(
-            f'invalid config: rule "{rule.ID}": should be '
-            f'either "enable", "disable" or a dict')
+            f'invalid config: rule "{rule.ID}": should be either "enable", '
+            f'"disable" or a dict')
 
     return conf
 
--- a/yamllint/rules/indentation.py
+++ b/yamllint/rules/indentation.py
@@ -342,11 +342,11 @@ def _check(conf, token, prev, next, nextnext, context):
 
         if found_indentation != expected:
             if expected < 0:
-                message = f'wrong indentation: expected ' \
-                          f'at least {found_indentation + 1}'
+                message = f'wrong indentation: expected at least ' \
+                          f'{found_indentation + 1}'
             else:
-                message = f'wrong indentation: expected {expected} ' \
-                          f'but found {found_indentation}'
+                message = f'wrong indentation: expected {expected} but ' \
+                          f'found {found_indentation}'
             yield LintProblem(token.start_mark.line + 1,
                               found_indentation + 1, message)
 

Thank you Dimitri, let's merge!