Prompt-toolkit

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New features:
- Improved custom dictionary completion:
* Also complete list indexes.
* Also complete attributes after doing a dictionary lookup.
* Also complete iterators in a for-loop.
- Added a 'title' option, so that applications embedding ptpython can set a
title in the status bar.

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- Fix backwards-compatibility of the `run_config` function. (used by
django-extensions).
- Fix input mode in status bar for block selection.

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Upgrade to prompt_toolkit 3.0.
Requires at least Python 3.6.

New features:
- Uses XDG base directory specification.

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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.