Python 37+ initial migration (#522)

* Initial migration to the python 3.7: Semi-automatic changes

CI related:
Update `tox.ini` and `.travis.yml` to run python3 only tests
Python 3.11 tests is commented-out on travis until #517 is not merged

Manual changes:
* `setup.py`: classifiers, remove python2 compatibility code
* `docs/manual/wcur2.py`: looks like file was never completed, syntax is invalid
* `urwid.compat`: removed `ord2`, `bytes3`, `text_type`, `xrange` and `text_types`

Automatic changes (no manual editing, AST validated equality:
* removed `u` prefix from all strings: not allowed in modern python code
* `bytes()` -> `b''`
* `== None` -> `is None`
* subclassing of `object`
* `super(<Class>`, self>)` ->`super()`
* `from __future__ import ...` python3 compatibility imports
* `set(<Iterable[Hashable]>)` -> `{<Hashable>}`
* partial f-strings conversion
* (`IOError`, `select.error`, `socket.error`) -> `OSError`

* Switch to f-strings (automatic changes)

* Remove `urwid.compat.B`

* Remove `urwid.compat.with_metaclass`

* use native `super()` instead of `self.__super`

* Remove `urwid.compat.chr2`

* Remove `urwid.split_repr.python3_repr`

* Use native `@classmethod` and `@property` where overload is not possible

* Add `from __future__ import annotations`

* automatically sort imports

* Add DeprecationWarning to the deprecated methods

most IDE's will recognize it and annotate during new code usage
call with "warnings as errors" mode will help to refactor other users

* Address comments

* replace homepage address in all files
* remove outdated comments in compat.py
* make wcur2.py correct python code. For example subclass
* replace `self.__super` by `super()` in examples
* fix asyncio_socket_server.py: magic with `asyncio` became wrong

* Remove `widget.update_wrapper`: this was backport of python `functools.update_wrapper`

* display_common.py: fix trivial typo in _colors calculation

* use `sorted` method instead of list construction with later sorting

* Address comments

* `wcur2` include in docs
* warning on `signals.Signals.emit`

---------

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

1 files changed, 8 insertions, 8 deletions

diff --git a/urwid/html_fragment.py b/urwid/html_fragment.py
index 5df9273..b14c57f 100755
--- a/urwid/html_fragment.py
+++ b/urwid/html_fragment.py
@@ -17,18 +17,18 @@
 #    License along with this library; if not, write to the Free Software
 #    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 #
-# Urwid web site: http://excess.org/urwid/
+# Urwid web site: https://urwid.org/
 
-from __future__ import division, print_function
 
 """
 HTML PRE-based UI implementation
 """
 
+from __future__ import annotations
+
 from urwid import util
-from urwid.main_loop import ExitMainLoop
 from urwid.display_common import AttrSpec, BaseScreen
-
+from urwid.main_loop import ExitMainLoop
 
 # replace control characters with ?'s
 _trans_table = "?" * 32 + "".join([chr(x) for x in range(32, 256)])
@@ -47,7 +47,7 @@ class HtmlGenerator(BaseScreen):
     started = True
 
     def __init__(self):
-        super(HtmlGenerator, self).__init__()
+        super().__init__()
         self.colors = 16
         self.bright_is_bold = False # ignored
         self.has_underline = True # ignored
@@ -124,7 +124,7 @@ class HtmlGenerator(BaseScreen):
             l.append("\n")
 
         # add the fragment to the list
-        self.fragments.append( "<pre>%s</pre>" % "".join(l) )
+        self.fragments.append( f"<pre>{''.join(l)}</pre>" )
 
     def clear(self):
         """
@@ -160,8 +160,8 @@ def html_span(s, aspec, cursor = -1):
         fg_r, fg_g, fg_b = _d_fg_r, _d_fg_g, _d_fg_b
     if bg_r is None:
         bg_r, bg_g, bg_b = _d_bg_r, _d_bg_g, _d_bg_b
-    html_fg = "#%02x%02x%02x" % (fg_r, fg_g, fg_b)
-    html_bg = "#%02x%02x%02x" % (bg_r, bg_g, bg_b)
+    html_fg = f"#{fg_r:02x}{fg_g:02x}{fg_b:02x}"
+    html_bg = f"#{bg_r:02x}{bg_g:02x}{bg_b:02x}"
     if aspec.standout:
         html_fg, html_bg = html_bg, html_fg
     extra = (";text-decoration:underline" * aspec.underline +