Stop using more-itertools

We barely use it; the couple places that do are not really worth the
extra dependency, I think the code is clearer without it.

Also simplifies one (regular) itertools usage.

Also improves a check and an error message in `pytest.raises`.

changelog/7587.trivial.rst

@@ -0,0 +1 @@
+The dependency on the ``more-itertools`` package has been removed.

setup.cfg

@@ -42,7 +42,6 @@ packages =
 install_requires =
     attrs>=17.4.0
     iniconfig
-    more-itertools>=4.0.0
     packaging
     pluggy>=0.12,<1.0
     py>=1.8.2

src/_pytest/fixtures.py

@@ -1,6 +1,5 @@
 import functools
 import inspect
-import itertools
 import sys
 import warnings
 from collections import defaultdict
@@ -1489,10 +1488,10 @@ class FixtureManager:
         else:
             argnames = ()
 
-        usefixtures = itertools.chain.from_iterable(
-            mark.args for mark in node.iter_markers(name="usefixtures")
+        usefixtures = tuple(
+            arg for mark in node.iter_markers(name="usefixtures") for arg in mark.args
         )
-        initialnames = tuple(usefixtures) + argnames
+        initialnames = usefixtures + argnames
         fm = node.session._fixturemanager
         initialnames, names_closure, arg2fixturedefs = fm.getfixtureclosure(
             initialnames, node, ignore_args=self._get_direct_parametrize_args(node)

src/_pytest/python_api.py

@@ -1,11 +1,9 @@
-import inspect
 import math
 import pprint
 from collections.abc import Iterable
 from collections.abc import Mapping
 from collections.abc import Sized
 from decimal import Decimal
-from itertools import filterfalse
 from numbers import Number
 from types import TracebackType
 from typing import Any
@@ -18,8 +16,6 @@ from typing import Tuple
 from typing import TypeVar
 from typing import Union
 
-from more_itertools.more import always_iterable
-
 import _pytest._code
 from _pytest.compat import overload
 from _pytest.compat import STRING_TYPES
@@ -30,9 +26,6 @@ if TYPE_CHECKING:
     from typing import Type
 
 
-BASE_TYPE = (type, STRING_TYPES)
-
-
 def _non_numeric_type_error(value, at: Optional[str]) -> TypeError:
     at_str = " at {}".format(at) if at else ""
     return TypeError(
@@ -680,11 +673,16 @@ def raises(  # noqa: F811
         documentation for :ref:`the try statement <python:try>`.
     """
     __tracebackhide__ = True
-    for exc in filterfalse(
-        inspect.isclass, always_iterable(expected_exception, BASE_TYPE)
-    ):
-        msg = "exceptions must be derived from BaseException, not %s"
-        raise TypeError(msg % type(exc))
+
+    if isinstance(expected_exception, type):
+        excepted_exceptions = (expected_exception,)  # type: Tuple[Type[_E], ...]
+    else:
+        excepted_exceptions = expected_exception
+    for exc in excepted_exceptions:
+        if not isinstance(exc, type) or not issubclass(exc, BaseException):
+            msg = "expected exception must be a BaseException type, not {}"
+            not_a = exc.__name__ if isinstance(exc, type) else type(exc).__name__
+            raise TypeError(msg.format(not_a))
 
     message = "DID NOT RAISE {}".format(expected_exception)
 

src/_pytest/terminal.py

@@ -25,7 +25,6 @@ from typing import Union
 import attr
 import pluggy
 import py
-from more_itertools import collapse
 
 import pytest
 from _pytest import nodes
@@ -715,11 +714,14 @@ class TerminalReporter:
             self._write_report_lines_from_hooks(lines)
 
     def _write_report_lines_from_hooks(
-        self, lines: List[Union[str, List[str]]]
+        self, lines: Sequence[Union[str, Sequence[str]]]
     ) -> None:
-        lines.reverse()
-        for line in collapse(lines):
-            self.write_line(line)
+        for line_or_lines in reversed(lines):
+            if isinstance(line_or_lines, str):
+                self.write_line(line_or_lines)
+            else:
+                for line in line_or_lines:
+                    self.write_line(line)
 
     def pytest_report_header(self, config: Config) -> List[str]:
         line = "rootdir: %s" % config.rootdir

testing/python/raises.py

@@ -283,3 +283,22 @@ class TestRaises:
             with pytest.raises(Exception, foo="bar"):  # type: ignore[call-overload]
                 pass
         assert "Unexpected keyword arguments" in str(excinfo.value)
+
+    def test_expected_exception_is_not_a_baseexception(self) -> None:
+        with pytest.raises(TypeError) as excinfo:
+            with pytest.raises("hello"):  # type: ignore[call-overload]
+                pass  # pragma: no cover
+        assert "must be a BaseException type, not str" in str(excinfo.value)
+
+        class NotAnException:
+            pass
+
+        with pytest.raises(TypeError) as excinfo:
+            with pytest.raises(NotAnException):  # type: ignore[type-var]
+                pass  # pragma: no cover
+        assert "must be a BaseException type, not NotAnException" in str(excinfo.value)
+
+        with pytest.raises(TypeError) as excinfo:
+            with pytest.raises(("hello", NotAnException)):  # type: ignore[arg-type]
+                pass  # pragma: no cover
+        assert "must be a BaseException type, not str" in str(excinfo.value)