Summary -- Release highlights¶

New checkers¶

String checker now reports format string type mismatches.
duplicate-string-formatting-argument was added for detecting duplicate string formatting arguments that should be passed instead as named arguments.
logging-format-style is a new option for the logging checker for usage of str.format() style format strings in calls to loggers.

It accepts two options: --logging-format-style=old for using % style formatting, which is the assumed default, and --logging-format-style=new for using {} style formatting.
implicit-str-concat-in-sequence detects string concatenation inside lists, sets & tuples.

Example of code that would generate such warning:
```
woops = ('a', 'b' 'c')
```

try-except-raise checker now handles multilevel inheritance hirerachy for exceptions correctly.

Closes #2484
Ignore import x.y.z as z cases for checker useless-import-alias.
unnecessary-pass is now also emitted when a function or class contains only docstring and pass statement, in which case, docstring is enough for empty definition.
Fix false positive undefined-variable and used-before-assignment with nonlocal keyword usage.
Fix exceptions being raised when one of the params is not a ClassDef for checkers.utils.is_subclass_of.
pylint now picks the latest value from the inferred values of the exception that gets raised, when looking for raising-non-exception. This helps when reusing a variable name for multiple types, since pylint was picking just the first inferred value, leading to spurious false positives.

Closes #2431
pylint used to emit a not-an-iterable error when looking at coroutines built with asyncio.coroutine. This is no longer the case as we handle coroutines explicitly.

Closes #996
pylint used to emit an unused-variable error if unused import was found in the function. Now instead of unused-variable, unused-import is emitted.

Closes #2421