... # nothing to split on - line too long
```
-So _Black_ will eventually format it like this:
+So _Black_ will, when we implement this, format it like this:
```py3
with \
- make_context_manager(1) as cm1, \
- make_context_manager(2) as cm2, \
- make_context_manager(3) as cm3, \
- make_context_manager(4) as cm4 \
+ make_context_manager1() as cm1, \
+ make_context_manager2() as cm2, \
+ make_context_manager3() as cm3, \
+ make_context_manager4() as cm4 \
:
... # backslashes and an ugly stranded colon
```
-Although when the target version is Python 3.9 or higher, _Black_ will use parentheses
-instead since they're allowed in Python 3.9 and higher.
+Although when the target version is Python 3.9 or higher, _Black_ uses parentheses
+instead in `--preview` mode (see below) since they're allowed in Python 3.9 and higher.
-## Improved string processing
+An alternative to consider if the backslashes in the above formatting are undesirable is
+to use {external:py:obj}`contextlib.ExitStack` to combine context managers in the
+following way:
-Currently, _Black_ does not split long strings to fit the line length limit. Currently,
-there is [an experimental option](labels/experimental-string) to enable splitting
-strings. We plan to enable this option by default once it is fully stable. This is
+```python
+with contextlib.ExitStack() as exit_stack:
+ cm1 = exit_stack.enter_context(make_context_manager1())
+ cm2 = exit_stack.enter_context(make_context_manager2())
+ cm3 = exit_stack.enter_context(make_context_manager3())
+ cm4 = exit_stack.enter_context(make_context_manager4())
+ ...
+```
+
+(labels/preview-style)=
+
+## Preview style
+
+Experimental, potentially disruptive style changes are gathered under the `--preview`
+CLI flag. At the end of each year, these changes may be adopted into the default style,
+as described in [The Black Code Style](index.md). Because the functionality is
+experimental, feedback and issue reports are highly encouraged!
+
+### Improved string processing
+
+_Black_ will split long string literals and merge short ones. Parentheses are used where
+appropriate. When split, parts of f-strings that don't need formatting are converted to
+plain strings. User-made splits are respected when they do not exceed the line length
+limit. Line continuation backslashes are converted into parenthesized strings.
+Unnecessary parentheses are stripped. The stability and status of this feature is
tracked in [this issue](https://github.com/psf/black/issues/2188).
+
+### Improved line breaks
+
+For assignment expressions, _Black_ now prefers to split and wrap the right side of the
+assignment instead of left side. For example:
+
+```python
+some_dict[
+ "with_a_long_key"
+] = some_looooooooong_module.some_looooooooooooooong_function_name(
+ first_argument, second_argument, third_argument
+)
+```
+
+will be changed to:
+
+```python
+some_dict["with_a_long_key"] = (
+ some_looooooooong_module.some_looooooooooooooong_function_name(
+ first_argument, second_argument, third_argument
+ )
+)
+```
+
+### Improved parentheses management
+
+For dict literals with long values, they are now wrapped in parentheses. Unnecessary
+parentheses are now removed. For example:
+
+```python
+my_dict = {
+ "a key in my dict": a_very_long_variable
+ * and_a_very_long_function_call()
+ / 100000.0,
+ "another key": (short_value),
+}
+```
+
+will be changed to:
+
+```python
+my_dict = {
+ "a key in my dict": (
+ a_very_long_variable * and_a_very_long_function_call() / 100000.0
+ ),
+ "another key": short_value,
+}
+```
+
+### Improved multiline string handling
+
+_Black_ is smarter when formatting multiline strings, especially in function arguments,
+to avoid introducing extra line breaks. Previously, it would always consider multiline
+strings as not fitting on a single line. With this new feature, _Black_ looks at the
+context around the multiline string to decide if it should be inlined or split to a
+separate line. For example, when a multiline string is passed to a function, _Black_
+will only split the multiline string if a line is too long or if multiple arguments are
+being passed.
+
+For example, _Black_ will reformat
+
+```python
+textwrap.dedent(
+ """\
+ This is a
+ multiline string
+"""
+)
+```
+
+to:
+
+```python
+textwrap.dedent("""\
+ This is a
+ multiline string
+""")
+```
+
+And:
+
+```python
+MULTILINE = """
+foobar
+""".replace(
+ "\n", ""
+)
+```
+
+to:
+
+```python
+MULTILINE = """
+foobar
+""".replace("\n", "")
+```
+
+Implicit multiline strings are special, because they can have inline comments. Strings
+without comments are merged, for example
+
+```python
+s = (
+ "An "
+ "implicit "
+ "multiline "
+ "string"
+)
+```
+
+becomes
+
+```python
+s = "An implicit multiline string"
+```
+
+A comment on any line of the string (or between two string lines) will block the
+merging, so
+
+```python
+s = (
+ "An " # Important comment concerning just this line
+ "implicit "
+ "multiline "
+ "string"
+)
+```
+
+and
+
+```python
+s = (
+ "An "
+ "implicit "
+ # Comment in between
+ "multiline "
+ "string"
+)
+```
+
+will not be merged. Having the comment after or before the string lines (but still
+inside the parens) will merge the string. For example
+
+```python
+s = ( # Top comment
+ "An "
+ "implicit "
+ "multiline "
+ "string"
+ # Bottom comment
+)
+```
+
+becomes
+
+```python
+s = ( # Top comment
+ "An implicit multiline string"
+ # Bottom comment
+)
+```
projects / etc / vim.git / blobdiff