diff --git a/mercurial/profiling.py b/mercurial/profiling.py
--- a/mercurial/profiling.py
+++ b/mercurial/profiling.py
@@ -272,7 +272,12 @@
                 exception_type, exception_value, traceback
             )
             if self._output == b'blackbox':
+                # We always use io.BytesIO if self._output == b"blackbox". But
+                # pytype doesn't realize this and thinks we're attempting to
+                # access .getvalue() on an IO type.
+                # pytype: disable=attribute-error
                 val = b'Profile:\n%s' % self._fp.getvalue()
+                # pytype: enable=attribute-error
                 # ui.log treats the input as a format string,
                 # so we need to escape any % signs.
                 val = val.replace(b'%', b'%%')
diff --git a/mercurial/pycompat.py b/mercurial/pycompat.py
--- a/mercurial/pycompat.py
+++ b/mercurial/pycompat.py
@@ -36,6 +36,16 @@
 
 if not globals():  # hide this from non-pytype users
     import typing
+    from typing import (
+        Any,
+        AnyStr,
+        Dict,
+        IO,
+        Iterator,
+        List,
+        NoReturn,
+        Tuple,
+    )
 
     TYPE_CHECKING = typing.TYPE_CHECKING
 
@@ -112,15 +122,15 @@
     sysexecutable = os.fsencode(sysexecutable)
 
 
-def maplist(*args):
+def maplist(*args) -> 'List[Any]':
     return list(map(*args))
 
 
-def rangelist(*args):
+def rangelist(*args) -> 'List[int]':
     return list(range(*args))
 
 
-def ziplist(*args):
+def ziplist(*args) -> 'List[Any]':
     return list(zip(*args))
 
 
@@ -226,20 +236,20 @@
             s = str(s).encode('ascii')
         return bytes.__new__(cls, s)
 
-    def __getitem__(self, key):
+    def __getitem__(self, key) -> bytes:
         s = bytes.__getitem__(self, key)
         if not isinstance(s, bytes):
             s = bytechr(s)
         return s
 
-    def __iter__(self):
+    def __iter__(self) -> 'Iterator[bytes]':
         return iterbytestr(bytes.__iter__(self))
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return bytes.__repr__(self)[1:]  # drop b''
 
 
-def iterbytestr(s):
+def iterbytestr(s) -> 'Iterator[bytes]':
     """Iterate bytes as if it were a str object of Python 2"""
     return map(bytechr, s)
 
@@ -251,7 +261,7 @@
     return s
 
 
-def sysbytes(s):
+def sysbytes(s) -> bytes:
     """Convert an internal str (e.g. keyword, __doc__) back to bytes
 
     This never raises UnicodeEncodeError, but only ASCII characters
@@ -262,7 +272,7 @@
     return s.encode('utf-8')
 
 
-def sysstr(s):
+def sysstr(s) -> str:
     """Return a keyword str to be passed to Python functions such as
     getattr() and str.encode()
 
@@ -275,26 +285,26 @@
     return s.decode('latin-1')
 
 
-def strurl(url):
+def strurl(url) -> str:
     """Converts a bytes url back to str"""
     if isinstance(url, bytes):
         return url.decode('ascii')
     return url
 
 
-def bytesurl(url):
+def bytesurl(url) -> bytes:
     """Converts a str url to bytes by encoding in ascii"""
     if isinstance(url, str):
         return url.encode('ascii')
     return url
 
 
-def raisewithtb(exc, tb):
+def raisewithtb(exc, tb) -> 'NoReturn':
     """Raise exception with the given traceback"""
     raise exc.with_traceback(tb)
 
 
-def getdoc(obj):
+def getdoc(obj) -> bytes:
     """Get docstring as bytes; may be None so gettext() won't confuse it
     with _('')"""
     doc = getattr(obj, '__doc__', None)
@@ -320,14 +330,16 @@
 unicode = str
 
 
-def open(name, mode=b'r', buffering=-1, encoding=None):
+def open(name, mode=b'r', buffering=-1, encoding=None) -> 'IO[AnyStr]':
     return builtins.open(name, sysstr(mode), buffering, encoding)
 
 
 safehasattr = _wrapattrfunc(builtins.hasattr)
 
 
-def _getoptbwrapper(orig, args, shortlist, namelist):
+def _getoptbwrapper(
+    orig, args, shortlist, namelist
+) -> 'Tuple[List[Tuple[bytes, bytes]], List[bytes]]':
     """
     Takes bytes arguments, converts them to unicode, pass them to
     getopt.getopt(), convert the returned values back to bytes and then
@@ -343,7 +355,7 @@
     return opts, args
 
 
-def strkwargs(dic):
+def strkwargs(dic) -> 'Dict[str, Any]':
     """
     Converts the keys of a python dictonary to str i.e. unicodes so that
     they can be passed as keyword arguments as dictionaries with bytes keys
@@ -353,7 +365,7 @@
     return dic
 
 
-def byteskwargs(dic):
+def byteskwargs(dic) -> 'Dict[bytes, Any]':
     """
     Converts keys of python dictionaries to bytes as they were converted to
     str to pass that dictonary as a keyword argument on Python 3.
@@ -363,7 +375,7 @@
 
 
 # TODO: handle shlex.shlex().
-def shlexsplit(s, comments=False, posix=True):
+def shlexsplit(s, comments=False, posix=True) -> 'List[bytes]':
     """
     Takes bytes argument, convert it to str i.e. unicodes, pass that into
     shlex.split(), convert the returned value to bytes and return that for
@@ -394,18 +406,18 @@
     return _getoptbwrapper(getopt.gnu_getopt, args, shortlist, namelist)
 
 
-def mkdtemp(suffix=b'', prefix=b'tmp', dir=None):
+def mkdtemp(suffix=b'', prefix=b'tmp', dir=None) -> 'AnyStr':
     return tempfile.mkdtemp(suffix, prefix, dir)
 
 
 # text=True is not supported; use util.from/tonativeeol() instead
-def mkstemp(suffix=b'', prefix=b'tmp', dir=None):
+def mkstemp(suffix=b'', prefix=b'tmp', dir=None) -> 'Tuple[int, AnyStr]':
     return tempfile.mkstemp(suffix, prefix, dir)
 
 
 # TemporaryFile does not support an "encoding=" argument on python2.
 # This wrapper file are always open in byte mode.
-def unnamedtempfile(mode=None, *args, **kwargs):
+def unnamedtempfile(mode=None, *args, **kwargs) -> 'IO[AnyStr]':
     if mode is None:
         mode = 'w+b'
     else: