Python: Drop support for Python 3.7

Debian 10 is not anymore a supported distro, since Debian 12 was
released on June 10, 2023.  Our supported build platforms as of today
all support at least 3.8 (and all of them except for Ubuntu 20.04
support 3.9):

openSUSE Leap 15.5: 3.6.15 (3.11.2)
CentOS Stream 8:    3.6.8  (3.8.13, 3.9.16, 3.11.4)
CentOS Stream 9:    3.9.17 (3.11.4)
Fedora 37:          3.11.4
Fedora 38:          3.11.4
Debian 11:          3.9.2
Debian 12:          3.11.2
Alpine 3.14, 3.15:  3.9.16
Alpine 3.16, 3.17:  3.10.10
Ubuntu 20.04 LTS:   3.8.10
Ubuntu 22.04 LTS:   3.10.12
NetBSD 9.3:         3.9.13*
FreeBSD 12.4:       3.9.16
FreeBSD 13.1:       3.9.18
OpenBSD 7.2:        3.9.17

Note: NetBSD does not appear to have a default meta-package, but offers
several options, the lowest of which is 3.7.15. However, "python39"
appears to be a pre-requisite to one of the other packages we request
in tests/vm/netbsd.

Since it is safe under our supported platform policy, bump our
minimum supported version of Python to 3.8.  The two most interesting
features to have by default include:

- the importlib.metadata module, whose lack is responsible for over 100
  lines of code in mkvenv.py

- improvements to asyncio, for example asyncio.CancelledError
  inherits from BaseException rather than Exception

In addition, code can now use the assignment operator ':='

Because mypy now learns about importlib.metadata, a small change to
mkvenv.py is needed to pass type checking.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

4 files changed, 12 insertions, 10 deletions

diff --git a/python/Makefile b/python/Makefile
index 7c70dcc8d1..1fa4ba2498 100644
--- a/python/Makefile
+++ b/python/Makefile
@@ -9,13 +9,13 @@ help:
 	@echo "make check-minreqs:"
 	@echo "    Run tests in the minreqs virtual environment."
 	@echo "    These tests use the oldest dependencies."
-	@echo "    Requires: Python 3.7"
-	@echo "    Hint (Fedora): 'sudo dnf install python3.7'"
+	@echo "    Requires: Python 3.8"
+	@echo "    Hint (Fedora): 'sudo dnf install python3.8'"
 	@echo ""
 	@echo "make check-tox:"
 	@echo "    Run tests against multiple python versions."
 	@echo "    These tests use the newest dependencies."
-	@echo "    Requires: Python 3.7 - 3.11, and tox."
+	@echo "    Requires: Python 3.8 - 3.11, and tox."
 	@echo "    Hint (Fedora): 'sudo dnf install python3-tox python3.11'"
 	@echo "    The variable QEMU_TOX_EXTRA_ARGS can be use to pass extra"
 	@echo "    arguments to tox".
@@ -59,7 +59,7 @@ PIP_INSTALL = pip install --disable-pip-version-check
 min-venv: $(QEMU_MINVENV_DIR) $(QEMU_MINVENV_DIR)/bin/activate
 $(QEMU_MINVENV_DIR) $(QEMU_MINVENV_DIR)/bin/activate: setup.cfg tests/minreqs.txt
 	@echo "VENV $(QEMU_MINVENV_DIR)"
-	@python3.7 -m venv $(QEMU_MINVENV_DIR)
+	@python3.8 -m venv $(QEMU_MINVENV_DIR)
 	@(								\
 		echo "ACTIVATE $(QEMU_MINVENV_DIR)";			\
 		. $(QEMU_MINVENV_DIR)/bin/activate;			\
diff --git a/python/scripts/mkvenv.py b/python/scripts/mkvenv.py
index 4f2349fbb6..57a2494803 100644
--- a/python/scripts/mkvenv.py
+++ b/python/scripts/mkvenv.py
@@ -435,6 +435,7 @@ def _gen_importlib(packages: Sequence[str]) -> Iterator[str]:
     try:
         # First preference: Python 3.8+ stdlib
         from importlib.metadata import (  # type: ignore
+            EntryPoint,
             PackageNotFoundError,
             distribution,
         )
@@ -442,6 +443,7 @@ def _gen_importlib(packages: Sequence[str]) -> Iterator[str]:
         logger.debug("%s", str(exc))
         # Second preference: Commonly available PyPI backport
         from importlib_metadata import (  # type: ignore
+            EntryPoint,
             PackageNotFoundError,
             distribution,
         )
@@ -449,7 +451,8 @@ def _gen_importlib(packages: Sequence[str]) -> Iterator[str]:
     def _generator() -> Iterator[str]:
         for package in packages:
             try:
-                entry_points = distribution(package).entry_points
+                entry_points: Iterator[EntryPoint] = \
+                    iter(distribution(package).entry_points)
             except PackageNotFoundError:
                 continue
 
diff --git a/python/setup.cfg b/python/setup.cfg
index e74b58a8c2..f6d2d8a136 100644
--- a/python/setup.cfg
+++ b/python/setup.cfg
@@ -14,7 +14,6 @@ classifiers =
     Natural Language :: English
     Operating System :: OS Independent
     Programming Language :: Python :: 3 :: Only
-    Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
     Programming Language :: Python :: 3.10
@@ -22,7 +21,7 @@ classifiers =
     Typing :: Typed
 
 [options]
-python_requires = >= 3.7
+python_requires = >= 3.8
 packages =
     qemu.qmp
     qemu.machine
@@ -76,7 +75,7 @@ exclude = __pycache__,
 
 [mypy]
 strict = True
-python_version = 3.7
+python_version = 3.8
 warn_unused_configs = True
 namespace_packages = True
 warn_unused_ignores = False
@@ -192,7 +191,7 @@ multi_line_output=3
 # of python available on your system to run this test.
 
 [tox:tox]
-envlist = py37, py38, py39, py310, py311
+envlist = py38, py39, py310, py311
 skip_missing_interpreters = true
 
 [testenv]
diff --git a/python/tests/minreqs.txt b/python/tests/minreqs.txt
index 979461be6b..a3f423efd8 100644
--- a/python/tests/minreqs.txt
+++ b/python/tests/minreqs.txt
@@ -1,5 +1,5 @@
 # This file lists the ***oldest possible dependencies*** needed to run
-# "make check" successfully under ***Python 3.7***. It is used primarily
+# "make check" successfully under ***Python 3.8***. It is used primarily
 # by GitLab CI to ensure that our stated minimum versions in setup.cfg
 # are truthful and regularly validated.
 #