Prompt-toolkit

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New features:
- Added `new_eventloop_with_inputhook` function.
- Set exception handler from within `Application.run_async`.
- Applied Black code style.

Fixes:
- No longer expect a working event loop in the `History` classes.
(Fix for special situations when a `ThreadedHistory` is created before the
event loop has been set up.)
- Accept an empty prompt continuation.
- A few fixes to the `Buffer` tempfile code.

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New features:
- (almost) 100% type annotated.
- Native asyncio instead of custom event loops.
- Added shift-based text selection (use shift+arrows to start selecting text).

Breaking changes:
- Python 2 support has been dropped. Minimal Python version is now 3.6,
although 3.7 is preferred (because of ContextVars).
- Native asyncio, so some async code becomes slightly different.
- The active `Application` became a contextvar. Which means that it should be
propagated correctly to the code that requires it. However, random other
threads or coroutines won't be able to know what the current application is.
- The dialog shortcuts API changed. All dialog functions now return an
`Application`. You still have to call either `run()` or `run_async` on the
`Application` object.
- The way inputhooks work is changed.
- `patch_stdout` now requires an `Application` as input.

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Bug fixes:
- Fixed `Application.run_system_command` on Windows.
- Fixed bug in ANSI text formatting: correctly handle 256/true color sequences.
- Fixed bug in WordCompleter. Provide completions when there's a space before
the cursor.

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Bug fixes:
- Fixes the issue where changes made to the buffer in the accept handler were
not reflected in the history.
- Fix in the application invalidate handler. This prevents a significant slow
down in some applications after some time (especially if there is a refresh
interval).
- Make `print_container` utility work if the input is not a pty.

New features:
- Underline non breaking spaces instead of rendering as '&'.
- Added mouse support for radio list.
- Support completion styles for `READLINE_LIKE` display method.
- Accept formatted text in the display text of completions.
- Added a `FuzzyCompleter` and `FuzzyWordCompleter`.
- Improved error handling in Application (avoid displaying a meaningless
AssertionError in many cases).

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Bug fixes:
- Fixed assertion in PromptSession: the style_transformation check was wrong.
- Removed 'default' attribute in PromptSession. Only ask for it in the
`prompt()` method. This fixes the issue that passing `default` once, will
store it for all consequent calls in the `PromptSession`.
- Ensure that `__pt_formatted_text__` always returns a `FormattedText`
instance. This fixes an issue with `print_formatted_text`.

New features:
- Improved handling of situations where stdin or stdout are not a terminal.
(Print warning instead of failing with an assertion.)
- Added `print_container` utility.
- Sound bell when attempting to edit read-only buffer.
- Handle page-down and page-up keys in RadioList.
- Accept any `collections.abc.Sequence` for HSplit/VSplit children (instead of
lists only).
- Improved Vi key bindings: return to navigation mode when Insert is pressed.

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Bug fixes:
- Don't use the predefined ANSI colors for colors that are defined as RGB.
(Terminals can assign different color schemes for ansi colors, and we don't
want use any of those for colors that are defined like aabbcc for instance.)
- Fix in handling of CPRs when patch_stdout is used.

Backwards incompatible changes:
- Change to the `Buffer` class. Reset the buffer unless the `accept_handler`
returns `True` (which means: "keep_text"). This doesn't affect applications
that use `PromptSession`.

New features:
- Added `AdjustBrightnessStyleTransformation`. This is a simple style
transformation that improves the rendering on terminals with light or dark
background.
- Improved performance (string width caching and line height calculation).
- Improved `TextArea`:
* Exposed `focus_on_click`.
* Added attributes: `auto_suggest`, `complete_while_typing`, `history`,
`get_line_prefix`, `input_processors`.
* Made attributes writable: `lexer`, `completer`, `complete_while_typing`,
`accept_handler`, `read_only`, `wrap_lines`.