diff --git a/src/_pytest/compat.py b/src/_pytest/compat.py
index 09e621c5d..fc810b3e5 100644
--- a/src/_pytest/compat.py
+++ b/src/_pytest/compat.py
@@ -10,11 +10,14 @@ import sys
 from contextlib import contextmanager
 from inspect import Parameter
 from inspect import signature
+from typing import Any
 from typing import Callable
 from typing import Generic
 from typing import Optional
 from typing import overload
+from typing import Tuple
 from typing import TypeVar
+from typing import Union
 
 import attr
 import py
@@ -46,7 +49,7 @@ else:
     import importlib_metadata  # noqa: F401
 
 
-def _format_args(func):
+def _format_args(func: Callable[..., Any]) -> str:
     return str(signature(func))
 
 
@@ -67,12 +70,12 @@ else:
     fspath = os.fspath
 
 
-def is_generator(func):
+def is_generator(func: object) -> bool:
     genfunc = inspect.isgeneratorfunction(func)
     return genfunc and not iscoroutinefunction(func)
 
 
-def iscoroutinefunction(func):
+def iscoroutinefunction(func: object) -> bool:
     """
     Return True if func is a coroutine function (a function defined with async
     def syntax, and doesn't contain yield), or a function decorated with
@@ -85,7 +88,7 @@ def iscoroutinefunction(func):
     return inspect.iscoroutinefunction(func) or getattr(func, "_is_coroutine", False)
 
 
-def getlocation(function, curdir=None):
+def getlocation(function, curdir=None) -> str:
     function = get_real_func(function)
     fn = py.path.local(inspect.getfile(function))
     lineno = function.__code__.co_firstlineno
@@ -94,7 +97,7 @@ def getlocation(function, curdir=None):
     return "%s:%d" % (fn, lineno + 1)
 
 
-def num_mock_patch_args(function):
+def num_mock_patch_args(function) -> int:
     """ return number of arguments used up by mock arguments (if any) """
     patchings = getattr(function, "patchings", None)
     if not patchings:
@@ -113,7 +116,13 @@ def num_mock_patch_args(function):
     )
 
 
-def getfuncargnames(function, *, name: str = "", is_method=False, cls=None):
+def getfuncargnames(
+    function: Callable[..., Any],
+    *,
+    name: str = "",
+    is_method: bool = False,
+    cls: Optional[type] = None
+) -> Tuple[str, ...]:
     """Returns the names of a function's mandatory arguments.
 
     This should return the names of all function arguments that:
@@ -181,7 +190,7 @@ else:
     from contextlib import nullcontext  # noqa
 
 
-def get_default_arg_names(function):
+def get_default_arg_names(function: Callable[..., Any]) -> Tuple[str, ...]:
     # Note: this code intentionally mirrors the code at the beginning of getfuncargnames,
     # to get the arguments which were excluded from its result because they had default values
     return tuple(
@@ -200,18 +209,18 @@ _non_printable_ascii_translate_table.update(
 )
 
 
-def _translate_non_printable(s):
+def _translate_non_printable(s: str) -> str:
     return s.translate(_non_printable_ascii_translate_table)
 
 
 STRING_TYPES = bytes, str
 
 
-def _bytes_to_ascii(val):
+def _bytes_to_ascii(val: bytes) -> str:
     return val.decode("ascii", "backslashreplace")
 
 
-def ascii_escaped(val):
+def ascii_escaped(val: Union[bytes, str]):
     """If val is pure ascii, returns it as a str().  Otherwise, escapes
     bytes objects into a sequence of escaped bytes:
 
@@ -308,7 +317,7 @@ def getimfunc(func):
         return func
 
 
-def safe_getattr(object, name, default):
+def safe_getattr(object: Any, name: str, default: Any) -> Any:
     """ Like getattr but return default upon any Exception or any OutcomeException.
 
     Attribute access can potentially fail for 'evil' Python objects.
@@ -322,7 +331,7 @@ def safe_getattr(object, name, default):
         return default
 
 
-def safe_isclass(obj):
+def safe_isclass(obj: object) -> bool:
     """Ignore any exception via isinstance on Python 3."""
     try:
         return inspect.isclass(obj)
@@ -343,21 +352,23 @@ COLLECT_FAKEMODULE_ATTRIBUTES = (
 )
 
 
-def _setup_collect_fakemodule():
+def _setup_collect_fakemodule() -> None:
     from types import ModuleType
     import pytest
 
-    pytest.collect = ModuleType("pytest.collect")
-    pytest.collect.__all__ = []  # used for setns
+    # Types ignored because the module is created dynamically.
+    pytest.collect = ModuleType("pytest.collect")  # type: ignore
+    pytest.collect.__all__ = []  # type: ignore  # used for setns
     for attr_name in COLLECT_FAKEMODULE_ATTRIBUTES:
-        setattr(pytest.collect, attr_name, getattr(pytest, attr_name))
+        setattr(pytest.collect, attr_name, getattr(pytest, attr_name))  # type: ignore
 
 
 class CaptureIO(io.TextIOWrapper):
-    def __init__(self):
+    def __init__(self) -> None:
         super().__init__(io.BytesIO(), encoding="UTF-8", newline="", write_through=True)
 
-    def getvalue(self):
+    def getvalue(self) -> str:
+        assert isinstance(self.buffer, io.BytesIO)
         return self.buffer.getvalue().decode("UTF-8")