Fix some check_untyped_defs = True mypy warnings

src/_pytest/_code/code.py

@@ -5,10 +5,15 @@ import traceback
 from inspect import CO_VARARGS
 from inspect import CO_VARKEYWORDS
 from traceback import format_exception_only
+from types import CodeType
 from types import TracebackType
+from typing import Any
+from typing import Dict
 from typing import Generic
+from typing import List
 from typing import Optional
 from typing import Pattern
+from typing import Set
 from typing import Tuple
 from typing import TypeVar
 from typing import Union
@@ -29,7 +34,7 @@ if False:  # TYPE_CHECKING
 class Code:
     """ wrapper around Python code objects """
 
-    def __init__(self, rawcode):
+    def __init__(self, rawcode) -> None:
         if not hasattr(rawcode, "co_filename"):
             rawcode = getrawcode(rawcode)
         try:
@@ -38,7 +43,7 @@ class Code:
             self.name = rawcode.co_name
         except AttributeError:
             raise TypeError("not a code object: {!r}".format(rawcode))
-        self.raw = rawcode
+        self.raw = rawcode  # type: CodeType
 
     def __eq__(self, other):
         return self.raw == other.raw
@@ -351,7 +356,7 @@ class Traceback(list):
         """ return the index of the frame/TracebackEntry where recursion
             originates if appropriate, None if no recursion occurred
         """
-        cache = {}
+        cache = {}  # type: Dict[Tuple[Any, int, int], List[Dict[str, Any]]]
         for i, entry in enumerate(self):
             # id for the code.raw is needed to work around
             # the strange metaprogramming in the decorator lib from pypi
@@ -650,7 +655,7 @@ class FormattedExcinfo:
                 args.append((argname, saferepr(argvalue)))
             return ReprFuncArgs(args)
 
-    def get_source(self, source, line_index=-1, excinfo=None, short=False):
+    def get_source(self, source, line_index=-1, excinfo=None, short=False) -> List[str]:
         """ return formatted and marked up source lines. """
         import _pytest._code
 
@@ -722,7 +727,7 @@ class FormattedExcinfo:
         else:
             line_index = entry.lineno - entry.getfirstlinesource()
 
-        lines = []
+        lines = []  # type: List[str]
         style = entry._repr_style
         if style is None:
             style = self.style
@@ -799,7 +804,7 @@ class FormattedExcinfo:
                 exc_msg=str(e),
                 max_frames=max_frames,
                 total=len(traceback),
-            )
+            )  # type: Optional[str]
             traceback = traceback[:max_frames] + traceback[-max_frames:]
         else:
             if recursionindex is not None:
@@ -812,10 +817,12 @@ class FormattedExcinfo:
 
     def repr_excinfo(self, excinfo):
 
-        repr_chain = []
+        repr_chain = (
+            []
+        )  # type: List[Tuple[ReprTraceback, Optional[ReprFileLocation], Optional[str]]]
         e = excinfo.value
         descr = None
-        seen = set()
+        seen = set()  # type: Set[int]
         while e is not None and id(e) not in seen:
             seen.add(id(e))
             if excinfo:
@@ -868,8 +875,8 @@ class TerminalRepr:
 
 
 class ExceptionRepr(TerminalRepr):
-    def __init__(self):
+    def __init__(self) -> None:
-        self.sections = []
+        self.sections = []  # type: List[Tuple[str, str, str]]
 
     def addsection(self, name, content, sep="-"):
         self.sections.append((name, content, sep))

src/_pytest/_code/source.py

@@ -7,6 +7,7 @@ import tokenize
 import warnings
 from ast import PyCF_ONLY_AST as _AST_FLAG
 from bisect import bisect_right
+from typing import List
 
 import py
 
@@ -19,11 +20,11 @@ class Source:
     _compilecounter = 0
 
     def __init__(self, *parts, **kwargs):
-        self.lines = lines = []
+        self.lines = lines = []  # type: List[str]
         de = kwargs.get("deindent", True)
         for part in parts:
             if not part:
-                partlines = []
+                partlines = []  # type: List[str]
             elif isinstance(part, Source):
                 partlines = part.lines
             elif isinstance(part, (tuple, list)):
@@ -157,8 +158,7 @@ class Source:
         source = "\n".join(self.lines) + "\n"
         try:
             co = compile(source, filename, mode, flag)
-        except SyntaxError:
+        except SyntaxError as ex:
-            ex = sys.exc_info()[1]
             # re-represent syntax errors from parsing python strings
             msglines = self.lines[: ex.lineno]
             if ex.offset:
@@ -173,7 +173,8 @@ class Source:
             if flag & _AST_FLAG:
                 return co
             lines = [(x + "\n") for x in self.lines]
-            linecache.cache[filename] = (1, None, lines, filename)
+            # Type ignored because linecache.cache is private.
+            linecache.cache[filename] = (1, None, lines, filename)  # type: ignore
             return co
 
 
@@ -282,7 +283,7 @@ def get_statement_startend2(lineno, node):
     return start, end
 
 
-def getstatementrange_ast(lineno, source, assertion=False, astnode=None):
+def getstatementrange_ast(lineno, source: Source, assertion=False, astnode=None):
     if astnode is None:
         content = str(source)
         # See #4260:

src/_pytest/assertion/__init__.py

@@ -2,6 +2,7 @@
 support for presenting detailed information in failing assertions.
 """
 import sys
+from typing import Optional
 
 from _pytest.assertion import rewrite
 from _pytest.assertion import truncate
@@ -52,7 +53,9 @@ def register_assert_rewrite(*names):
             importhook = hook
             break
     else:
-        importhook = DummyRewriteHook()
+        # TODO(typing): Add a protocol for mark_rewrite() and use it
+        # for importhook and for PytestPluginManager.rewrite_hook.
+        importhook = DummyRewriteHook()  # type: ignore
     importhook.mark_rewrite(*names)
 
 
@@ -69,7 +72,7 @@ class AssertionState:
     def __init__(self, config, mode):
         self.mode = mode
         self.trace = config.trace.root.get("assertion")
-        self.hook = None
+        self.hook = None  # type: Optional[rewrite.AssertionRewritingHook]
 
 
 def install_importhook(config):
@@ -108,6 +111,7 @@ def pytest_runtest_setup(item):
     """
 
     def callbinrepr(op, left, right):
+        # type: (str, object, object) -> Optional[str]
         """Call the pytest_assertrepr_compare hook and prepare the result
 
         This uses the first result from the hook and then ensures the
@@ -133,12 +137,13 @@ def pytest_runtest_setup(item):
                 if item.config.getvalue("assertmode") == "rewrite":
                     res = res.replace("%", "%%")
                 return res
+        return None
 
     util._reprcompare = callbinrepr
 
     if item.ihook.pytest_assertion_pass.get_hookimpls():
 
-        def call_assertion_pass_hook(lineno, expl, orig):
+        def call_assertion_pass_hook(lineno, orig, expl):
             item.ihook.pytest_assertion_pass(
                 item=item, lineno=lineno, orig=orig, expl=expl
             )

src/_pytest/assertion/rewrite.py

@@ -17,6 +17,7 @@ from typing import Dict
 from typing import List
 from typing import Optional
 from typing import Set
+from typing import Tuple
 
 import atomicwrites
 
@@ -48,13 +49,13 @@ class AssertionRewritingHook(importlib.abc.MetaPathFinder):
         except ValueError:
             self.fnpats = ["test_*.py", "*_test.py"]
         self.session = None
-        self._rewritten_names = set()
+        self._rewritten_names = set()  # type: Set[str]
-        self._must_rewrite = set()
+        self._must_rewrite = set()  # type: Set[str]
         # flag to guard against trying to rewrite a pyc file while we are already writing another pyc file,
         # which might result in infinite recursion (#3506)
         self._writing_pyc = False
         self._basenames_to_check_rewrite = {"conftest"}
-        self._marked_for_rewrite_cache = {}
+        self._marked_for_rewrite_cache = {}  # type: Dict[str, bool]
         self._session_paths_checked = False
 
     def set_session(self, session):
@@ -203,7 +204,7 @@ class AssertionRewritingHook(importlib.abc.MetaPathFinder):
 
         return self._is_marked_for_rewrite(name, state)
 
-    def _is_marked_for_rewrite(self, name, state):
+    def _is_marked_for_rewrite(self, name: str, state):
         try:
             return self._marked_for_rewrite_cache[name]
         except KeyError:
@@ -218,7 +219,7 @@ class AssertionRewritingHook(importlib.abc.MetaPathFinder):
             self._marked_for_rewrite_cache[name] = False
             return False
 
-    def mark_rewrite(self, *names):
+    def mark_rewrite(self, *names: str) -> None:
         """Mark import names as needing to be rewritten.
 
         The named module or package as well as any nested modules will
@@ -385,6 +386,7 @@ def _format_boolop(explanations, is_or):
 
 
 def _call_reprcompare(ops, results, expls, each_obj):
+    # type: (Tuple[str, ...], Tuple[bool, ...], Tuple[str, ...], Tuple[object, ...]) -> str
     for i, res, expl in zip(range(len(ops)), results, expls):
         try:
             done = not res
@@ -400,11 +402,13 @@ def _call_reprcompare(ops, results, expls, each_obj):
 
 
 def _call_assertion_pass(lineno, orig, expl):
+    # type: (int, str, str) -> None
     if util._assertion_pass is not None:
-        util._assertion_pass(lineno=lineno, orig=orig, expl=expl)
+        util._assertion_pass(lineno, orig, expl)
 
 
 def _check_if_assertion_pass_impl():
+    # type: () -> bool
     """Checks if any plugins implement the pytest_assertion_pass hook
     in order not to generate explanation unecessarily (might be expensive)"""
     return True if util._assertion_pass else False
@@ -578,7 +582,7 @@ class AssertionRewriter(ast.NodeVisitor):
     def _assert_expr_to_lineno(self):
         return _get_assertion_exprs(self.source)
 
-    def run(self, mod):
+    def run(self, mod: ast.Module) -> None:
         """Find all assert statements in *mod* and rewrite them."""
         if not mod.body:
             # Nothing to do.
@@ -620,12 +624,12 @@ class AssertionRewriter(ast.NodeVisitor):
         ]
         mod.body[pos:pos] = imports
         # Collect asserts.
-        nodes = [mod]
+        nodes = [mod]  # type: List[ast.AST]
         while nodes:
             node = nodes.pop()
             for name, field in ast.iter_fields(node):
                 if isinstance(field, list):
-                    new = []
+                    new = []  # type: List
                     for i, child in enumerate(field):
                         if isinstance(child, ast.Assert):
                             # Transform assert.
@@ -699,7 +703,7 @@ class AssertionRewriter(ast.NodeVisitor):
         .explanation_param().
 
         """
-        self.explanation_specifiers = {}
+        self.explanation_specifiers = {}  # type: Dict[str, ast.expr]
         self.stack.append(self.explanation_specifiers)
 
     def pop_format_context(self, expl_expr):
@@ -742,7 +746,8 @@ class AssertionRewriter(ast.NodeVisitor):
             from _pytest.warning_types import PytestAssertRewriteWarning
             import warnings
 
-            warnings.warn_explicit(
+            # Ignore type: typeshed bug https://github.com/python/typeshed/pull/3121
+            warnings.warn_explicit(  # type: ignore
                 PytestAssertRewriteWarning(
                     "assertion is always true, perhaps remove parentheses?"
                 ),
@@ -751,15 +756,15 @@ class AssertionRewriter(ast.NodeVisitor):
                 lineno=assert_.lineno,
             )
 
-        self.statements = []
+        self.statements = []  # type: List[ast.stmt]
-        self.variables = []
+        self.variables = []  # type: List[str]
         self.variable_counter = itertools.count()
 
         if self.enable_assertion_pass_hook:
-            self.format_variables = []
+            self.format_variables = []  # type: List[str]
 
-        self.stack = []
+        self.stack = []  # type: List[Dict[str, ast.expr]]
-        self.expl_stmts = []
+        self.expl_stmts = []  # type: List[ast.stmt]
         self.push_format_context()
         # Rewrite assert into a bunch of statements.
         top_condition, explanation = self.visit(assert_.test)
@@ -897,7 +902,7 @@ warn_explicit(
         # Process each operand, short-circuiting if needed.
         for i, v in enumerate(boolop.values):
             if i:
-                fail_inner = []
+                fail_inner = []  # type: List[ast.stmt]
                 # cond is set in a prior loop iteration below
                 self.expl_stmts.append(ast.If(cond, fail_inner, []))  # noqa
                 self.expl_stmts = fail_inner
@@ -908,10 +913,10 @@ warn_explicit(
             call = ast.Call(app, [expl_format], [])
             self.expl_stmts.append(ast.Expr(call))
             if i < levels:
-                cond = res
+                cond = res  # type: ast.expr
                 if is_or:
                     cond = ast.UnaryOp(ast.Not(), cond)
-                inner = []
+                inner = []  # type: List[ast.stmt]
                 self.statements.append(ast.If(cond, inner, []))
                 self.statements = body = inner
         self.statements = save
@@ -977,7 +982,7 @@ warn_explicit(
         expl = pat % (res_expl, res_expl, value_expl, attr.attr)
         return res, expl
 
-    def visit_Compare(self, comp):
+    def visit_Compare(self, comp: ast.Compare):
         self.push_format_context()
         left_res, left_expl = self.visit(comp.left)
         if isinstance(comp.left, (ast.Compare, ast.BoolOp)):
@@ -1010,7 +1015,7 @@ warn_explicit(
             ast.Tuple(results, ast.Load()),
         )
         if len(comp.ops) > 1:
-            res = ast.BoolOp(ast.And(), load_names)
+            res = ast.BoolOp(ast.And(), load_names)  # type: ast.expr
         else:
             res = load_names[0]
         return res, self.explanation_param(self.pop_format_context(expl_call))

src/_pytest/assertion/util.py

@@ -1,6 +1,9 @@
 """Utilities for assertion debugging"""
 import pprint
 from collections.abc import Sequence
+from typing import Callable
+from typing import List
+from typing import Optional
 
 import _pytest._code
 from _pytest import outcomes
@@ -10,11 +13,11 @@ from _pytest._io.saferepr import saferepr
 # interpretation code and assertion rewriter to detect this plugin was
 # loaded and in turn call the hooks defined here as part of the
 # DebugInterpreter.
-_reprcompare = None
+_reprcompare = None  # type: Optional[Callable[[str, object, object], Optional[str]]]
 
 # Works similarly as _reprcompare attribute. Is populated with the hook call
 # when pytest_runtest_setup is called.
-_assertion_pass = None
+_assertion_pass = None  # type: Optional[Callable[[int, str, str], None]]
 
 
 def format_explanation(explanation):
@@ -177,7 +180,7 @@ def _diff_text(left, right, verbose=0):
     """
     from difflib import ndiff
 
-    explanation = []
+    explanation = []  # type: List[str]
 
     def escape_for_readable_diff(binary_text):
         """
@@ -235,7 +238,7 @@ def _compare_eq_verbose(left, right):
     left_lines = repr(left).splitlines(keepends)
     right_lines = repr(right).splitlines(keepends)
 
-    explanation = []
+    explanation = []  # type: List[str]
     explanation += ["-" + line for line in left_lines]
     explanation += ["+" + line for line in right_lines]
 
@@ -259,7 +262,7 @@ def _compare_eq_iterable(left, right, verbose=0):
 
 def _compare_eq_sequence(left, right, verbose=0):
     comparing_bytes = isinstance(left, bytes) and isinstance(right, bytes)
-    explanation = []
+    explanation = []  # type: List[str]
     len_left = len(left)
     len_right = len(right)
     for i in range(min(len_left, len_right)):
@@ -327,7 +330,7 @@ def _compare_eq_set(left, right, verbose=0):
 
 
 def _compare_eq_dict(left, right, verbose=0):
-    explanation = []
+    explanation = []  # type: List[str]
     set_left = set(left)
     set_right = set(right)
     common = set_left.intersection(set_right)

src/_pytest/config/__init__.py

@@ -9,6 +9,15 @@ import types
 import warnings
 from functools import lru_cache
 from pathlib import Path
+from types import TracebackType
+from typing import Any
+from typing import Callable
+from typing import Dict
+from typing import List
+from typing import Optional
+from typing import Sequence
+from typing import Set
+from typing import Tuple
 
 import attr
 import py
@@ -32,6 +41,10 @@ from _pytest.outcomes import fail
 from _pytest.outcomes import Skipped
 from _pytest.warning_types import PytestConfigWarning
 
+if False:  # TYPE_CHECKING
+    from typing import Type
+
+
 hookimpl = HookimplMarker("pytest")
 hookspec = HookspecMarker("pytest")
 
@@ -40,7 +53,7 @@ class ConftestImportFailure(Exception):
     def __init__(self, path, excinfo):
         Exception.__init__(self, path, excinfo)
         self.path = path
-        self.excinfo = excinfo
+        self.excinfo = excinfo  # type: Tuple[Type[Exception], Exception, TracebackType]
 
 
 def main(args=None, plugins=None):
@@ -237,14 +250,18 @@ class PytestPluginManager(PluginManager):
 
     def __init__(self):
         super().__init__("pytest")
-        self._conftest_plugins = set()
+        # The objects are module objects, only used generically.
+        self._conftest_plugins = set()  # type: Set[object]
 
         # state related to local conftest plugins
-        self._dirpath2confmods = {}
+        # Maps a py.path.local to a list of module objects.
-        self._conftestpath2mod = {}
+        self._dirpath2confmods = {}  # type: Dict[Any, List[object]]
+        # Maps a py.path.local to a module object.
+        self._conftestpath2mod = {}  # type: Dict[Any, object]
         self._confcutdir = None
         self._noconftest = False
-        self._duplicatepaths = set()
+        # Set of py.path.local's.
+        self._duplicatepaths = set()  # type: Set[Any]
 
         self.add_hookspecs(_pytest.hookspec)
         self.register(self)
@@ -653,7 +670,7 @@ class Config:
 
         args = attr.ib()
         plugins = attr.ib()
-        dir = attr.ib()
+        dir = attr.ib(type=Path)
 
     def __init__(self, pluginmanager, *, invocation_params=None):
         from .argparsing import Parser, FILE_OR_DIR
@@ -674,10 +691,10 @@ class Config:
         self.pluginmanager = pluginmanager
         self.trace = self.pluginmanager.trace.root.get("config")
         self.hook = self.pluginmanager.hook
-        self._inicache = {}
+        self._inicache = {}  # type: Dict[str, Any]
-        self._override_ini = ()
+        self._override_ini = ()  # type: Sequence[str]
-        self._opt2dest = {}
+        self._opt2dest = {}  # type: Dict[str, str]
-        self._cleanup = []
+        self._cleanup = []  # type: List[Callable[[], None]]
         self.pluginmanager.register(self, "pytestconfig")
         self._configured = False
         self.hook.pytest_addoption.call_historic(kwargs=dict(parser=self._parser))
@@ -778,7 +795,7 @@ class Config:
     def pytest_load_initial_conftests(self, early_config):
         self.pluginmanager._set_initial_conftests(early_config.known_args_namespace)
 
-    def _initini(self, args):
+    def _initini(self, args) -> None:
         ns, unknown_args = self._parser.parse_known_and_unknown_args(
             args, namespace=copy.copy(self.option)
         )
@@ -879,8 +896,7 @@ class Config:
             self.hook.pytest_load_initial_conftests(
                 early_config=self, args=args, parser=self._parser
             )
-        except ConftestImportFailure:
+        except ConftestImportFailure as e:
-            e = sys.exc_info()[1]
             if ns.help or ns.version:
                 # we don't want to prevent --help/--version to work
                 # so just let is pass and print a warning at the end
@@ -946,7 +962,7 @@ class Config:
         assert isinstance(x, list)
         x.append(line)  # modifies the cached list inline
 
-    def getini(self, name):
+    def getini(self, name: str):
         """ return configuration value from an :ref:`ini file <inifiles>`. If the
         specified name hasn't been registered through a prior
         :py:func:`parser.addini <_pytest.config.Parser.addini>`
@@ -957,7 +973,7 @@ class Config:
             self._inicache[name] = val = self._getini(name)
             return val
 
-    def _getini(self, name):
+    def _getini(self, name: str) -> Any:
         try:
             description, type, default = self._parser._inidict[name]
         except KeyError:
@@ -1002,7 +1018,7 @@ class Config:
             values.append(relroot)
         return values
 
-    def _get_override_ini_value(self, name):
+    def _get_override_ini_value(self, name: str) -> Optional[str]:
         value = None
         # override_ini is a list of "ini=value" options
         # always use the last item if multiple values are set for same ini-name,
@@ -1017,7 +1033,7 @@ class Config:
                     value = user_ini_value
         return value
 
-    def getoption(self, name, default=notset, skip=False):
+    def getoption(self, name: str, default=notset, skip: bool = False):
         """ return command line option value.
 
         :arg name: name of the option.  You may also specify

src/_pytest/config/argparsing.py

@@ -2,6 +2,11 @@ import argparse
 import sys
 import warnings
 from gettext import gettext
+from typing import Any
+from typing import Dict
+from typing import List
+from typing import Optional
+from typing import Tuple
 
 import py
 
@@ -21,12 +26,12 @@ class Parser:
 
     def __init__(self, usage=None, processopt=None):
         self._anonymous = OptionGroup("custom options", parser=self)
-        self._groups = []
+        self._groups = []  # type: List[OptionGroup]
         self._processopt = processopt
         self._usage = usage
-        self._inidict = {}
+        self._inidict = {}  # type: Dict[str, Tuple[str, Optional[str], Any]]
-        self._ininames = []
+        self._ininames = []  # type: List[str]
-        self.extra_info = {}
+        self.extra_info = {}  # type: Dict[str, Any]
 
     def processoption(self, option):
         if self._processopt:
@@ -80,7 +85,7 @@ class Parser:
         args = [str(x) if isinstance(x, py.path.local) else x for x in args]
         return self.optparser.parse_args(args, namespace=namespace)
 
-    def _getparser(self):
+    def _getparser(self) -> "MyOptionParser":
         from _pytest._argcomplete import filescompleter
 
         optparser = MyOptionParser(self, self.extra_info, prog=self.prog)
@@ -94,7 +99,10 @@ class Parser:
                     a = option.attrs()
                     arggroup.add_argument(*n, **a)
         # bash like autocompletion for dirs (appending '/')
-        optparser.add_argument(FILE_OR_DIR, nargs="*").completer = filescompleter
+        # Type ignored because typeshed doesn't know about argcomplete.
+        optparser.add_argument(  # type: ignore
+            FILE_OR_DIR, nargs="*"
+        ).completer = filescompleter
         return optparser
 
     def parse_setoption(self, args, option, namespace=None):
@@ -103,13 +111,15 @@ class Parser:
             setattr(option, name, value)
         return getattr(parsedoption, FILE_OR_DIR)
 
-    def parse_known_args(self, args, namespace=None):
+    def parse_known_args(self, args, namespace=None) -> argparse.Namespace:
         """parses and returns a namespace object with known arguments at this
         point.
         """
         return self.parse_known_and_unknown_args(args, namespace=namespace)[0]
 
-    def parse_known_and_unknown_args(self, args, namespace=None):
+    def parse_known_and_unknown_args(
+        self, args, namespace=None
+    ) -> Tuple[argparse.Namespace, List[str]]:
         """parses and returns a namespace object with known arguments, and
         the remaining arguments unknown at this point.
         """
@@ -163,8 +173,8 @@ class Argument:
     def __init__(self, *names, **attrs):
         """store parms in private vars for use in add_argument"""
         self._attrs = attrs
-        self._short_opts = []
+        self._short_opts = []  # type: List[str]
-        self._long_opts = []
+        self._long_opts = []  # type: List[str]
         self.dest = attrs.get("dest")
         if "%default" in (attrs.get("help") or ""):
             warnings.warn(
@@ -268,8 +278,8 @@ class Argument:
                     )
                 self._long_opts.append(opt)
 
-    def __repr__(self):
+    def __repr__(self) -> str:
-        args = []
+        args = []  # type: List[str]
         if self._short_opts:
             args += ["_short_opts: " + repr(self._short_opts)]
         if self._long_opts:
@@ -286,7 +296,7 @@ class OptionGroup:
     def __init__(self, name, description="", parser=None):
         self.name = name
         self.description = description
-        self.options = []
+        self.options = []  # type: List[Argument]
         self.parser = parser
 
     def addoption(self, *optnames, **attrs):
@@ -421,7 +431,7 @@ class DropShorterLongHelpFormatter(argparse.HelpFormatter):
         option_map = getattr(action, "map_long_option", {})
         if option_map is None:
             option_map = {}
-        short_long = {}
+        short_long = {}  # type: Dict[str, str]
         for option in options:
             if len(option) == 2 or option[2] == " ":
                 continue

src/_pytest/config/findpaths.py

@@ -1,10 +1,15 @@
 import os
+from typing import List
+from typing import Optional
 
 import py
 
 from .exceptions import UsageError
 from _pytest.outcomes import fail
 
+if False:
+    from . import Config  # noqa: F401
+
 
 def exists(path, ignore=EnvironmentError):
     try:
@@ -102,7 +107,12 @@ def get_dirs_from_args(args):
 CFG_PYTEST_SECTION = "[pytest] section in {filename} files is no longer supported, change to [tool:pytest] instead."
 
 
-def determine_setup(inifile, args, rootdir_cmd_arg=None, config=None):
+def determine_setup(
+    inifile: str,
+    args: List[str],
+    rootdir_cmd_arg: Optional[str] = None,
+    config: Optional["Config"] = None,
+):
     dirs = get_dirs_from_args(args)
     if inifile:
         iniconfig = py.iniconfig.IniConfig(inifile)

src/_pytest/mark/evaluate.py

@@ -51,6 +51,8 @@ class MarkEvaluator:
         except TEST_OUTCOME:
             self.exc = sys.exc_info()
             if isinstance(self.exc[1], SyntaxError):
+                # TODO: Investigate why SyntaxError.offset is Optional, and if it can be None here.
+                assert self.exc[1].offset is not None
                 msg = [" " * (self.exc[1].offset + 4) + "^"]
                 msg.append("SyntaxError: invalid syntax")
             else:

src/_pytest/mark/structures.py

@@ -292,7 +292,7 @@ class MarkGenerator:
     _config = None
     _markers = set()  # type: Set[str]
 
-    def __getattr__(self, name):
+    def __getattr__(self, name: str) -> MarkDecorator:
         if name[0] == "_":
             raise AttributeError("Marker name must NOT start with underscore")
 

src/_pytest/nodes.py

@@ -1,14 +1,26 @@
 import os
 import warnings
 from functools import lru_cache
+from typing import Any
+from typing import Dict
+from typing import List
+from typing import Set
+from typing import Tuple
+from typing import Union
 
 import py
 
 import _pytest._code
 from _pytest.compat import getfslineno
+from _pytest.mark.structures import Mark
+from _pytest.mark.structures import MarkDecorator
 from _pytest.mark.structures import NodeKeywords
 from _pytest.outcomes import fail
 
+if False:  # TYPE_CHECKING
+    # Imported here due to circular import.
+    from _pytest.fixtures import FixtureDef
+
 SEP = "/"
 
 tracebackcutdir = py.path.local(_pytest.__file__).dirpath()
@@ -78,13 +90,13 @@ class Node:
         self.keywords = NodeKeywords(self)
 
         #: the marker objects belonging to this node
-        self.own_markers = []
+        self.own_markers = []  # type: List[Mark]
 
         #: allow adding of extra keywords to use for matching
-        self.extra_keyword_matches = set()
+        self.extra_keyword_matches = set()  # type: Set[str]
 
         # used for storing artificial fixturedefs for direct parametrization
-        self._name2pseudofixturedef = {}
+        self._name2pseudofixturedef = {}  # type: Dict[str, FixtureDef]
 
         if nodeid is not None:
             assert "::()" not in nodeid
@@ -127,7 +139,8 @@ class Node:
                 )
             )
         path, lineno = get_fslocation_from_item(self)
-        warnings.warn_explicit(
+        # Type ignored: https://github.com/python/typeshed/pull/3121
+        warnings.warn_explicit(  # type: ignore
             warning,
             category=None,
             filename=str(path),
@@ -160,7 +173,9 @@ class Node:
         chain.reverse()
         return chain
 
-    def add_marker(self, marker, append=True):
+    def add_marker(
+        self, marker: Union[str, MarkDecorator], append: bool = True
+    ) -> None:
         """dynamically add a marker object to the node.
 
         :type marker: ``str`` or ``pytest.mark.*``  object
@@ -168,17 +183,19 @@ class Node:
             ``append=True`` whether to append the marker,
             if ``False`` insert at position ``0``.
         """
-        from _pytest.mark import MarkDecorator, MARK_GEN
+        from _pytest.mark import MARK_GEN
 
-        if isinstance(marker, str):
+        if isinstance(marker, MarkDecorator):
-            marker = getattr(MARK_GEN, marker)
+            marker_ = marker
-        elif not isinstance(marker, MarkDecorator):
+        elif isinstance(marker, str):
-            raise ValueError("is not a string or pytest.mark.* Marker")
+            marker_ = getattr(MARK_GEN, marker)
-        self.keywords[marker.name] = marker
-        if append:
-            self.own_markers.append(marker.mark)
         else:
-            self.own_markers.insert(0, marker.mark)
+            raise ValueError("is not a string or pytest.mark.* Marker")
+        self.keywords[marker_.name] = marker
+        if append:
+            self.own_markers.append(marker_.mark)
+        else:
+            self.own_markers.insert(0, marker_.mark)
 
     def iter_markers(self, name=None):
         """
@@ -211,7 +228,7 @@ class Node:
 
     def listextrakeywords(self):
         """ Return a set of all extra keywords in self and any parents."""
-        extra_keywords = set()
+        extra_keywords = set()  # type: Set[str]
         for item in self.listchain():
             extra_keywords.update(item.extra_keyword_matches)
         return extra_keywords
@@ -239,7 +256,8 @@ class Node:
         pass
 
     def _repr_failure_py(self, excinfo, style=None):
-        if excinfo.errisinstance(fail.Exception):
+        # Type ignored: see comment where fail.Exception is defined.
+        if excinfo.errisinstance(fail.Exception):  # type: ignore
             if not excinfo.value.pytrace:
                 return str(excinfo.value)
         fm = self.session._fixturemanager
@@ -385,13 +403,13 @@ class Item(Node):
 
     def __init__(self, name, parent=None, config=None, session=None, nodeid=None):
         super().__init__(name, parent, config, session, nodeid=nodeid)
-        self._report_sections = []
+        self._report_sections = []  # type: List[Tuple[str, str, str]]
 
         #: user properties is a list of tuples (name, value) that holds user
         #: defined properties for this test.
-        self.user_properties = []
+        self.user_properties = []  # type: List[Tuple[str, Any]]
 
-    def add_report_section(self, when, key, content):
+    def add_report_section(self, when: str, key: str, content: str) -> None:
         """
         Adds a new report section, similar to what's done internally to add stdout and
         stderr captured output::

src/_pytest/reports.py

@@ -1,5 +1,6 @@
 from pprint import pprint
 from typing import Optional
+from typing import Union
 
 import py
 
@@ -221,7 +222,6 @@ class BaseReport:
                 reprcrash = reportdict["longrepr"]["reprcrash"]
 
                 unserialized_entries = []
-                reprentry = None
                 for entry_data in reprtraceback["reprentries"]:
                     data = entry_data["data"]
                     entry_type = entry_data["type"]
@@ -242,7 +242,7 @@ class BaseReport:
                             reprlocals=reprlocals,
                             filelocrepr=reprfileloc,
                             style=data["style"],
-                        )
+                        )  # type: Union[ReprEntry, ReprEntryNative]
                     elif entry_type == "ReprEntryNative":
                         reprentry = ReprEntryNative(data["lines"])
                     else:
@@ -352,7 +352,8 @@ class TestReport(BaseReport):
             if not isinstance(excinfo, ExceptionInfo):
                 outcome = "failed"
                 longrepr = excinfo
-            elif excinfo.errisinstance(skip.Exception):
+            # Type ignored -- see comment where skip.Exception is defined.
+            elif excinfo.errisinstance(skip.Exception):  # type: ignore
                 outcome = "skipped"
                 r = excinfo._getreprcrash()
                 longrepr = (str(r.path), r.lineno, r.message)

src/_pytest/runner.py

@@ -3,6 +3,10 @@ import bdb
 import os
 import sys
 from time import time
+from typing import Callable
+from typing import Dict
+from typing import List
+from typing import Tuple
 
 import attr
 
@@ -10,10 +14,14 @@ from .reports import CollectErrorRepr
 from .reports import CollectReport
 from .reports import TestReport
 from _pytest._code.code import ExceptionInfo
+from _pytest.nodes import Node
 from _pytest.outcomes import Exit
 from _pytest.outcomes import Skipped
 from _pytest.outcomes import TEST_OUTCOME
 
+if False:  # TYPE_CHECKING
+    from typing import Type
+
 #
 # pytest plugin hooks
 
@@ -118,6 +126,7 @@ def pytest_runtest_call(item):
     except Exception:
         # Store trace info to allow postmortem debugging
         type, value, tb = sys.exc_info()
+        assert tb is not None
         tb = tb.tb_next  # Skip *this* frame
         sys.last_type = type
         sys.last_value = value
@@ -185,7 +194,7 @@ def check_interactive_exception(call, report):
 def call_runtest_hook(item, when, **kwds):
     hookname = "pytest_runtest_" + when
     ihook = getattr(item.ihook, hookname)
-    reraise = (Exit,)
+    reraise = (Exit,)  # type: Tuple[Type[BaseException], ...]
     if not item.config.getoption("usepdb", False):
         reraise += (KeyboardInterrupt,)
     return CallInfo.from_call(
@@ -252,7 +261,8 @@ def pytest_make_collect_report(collector):
         skip_exceptions = [Skipped]
         unittest = sys.modules.get("unittest")
         if unittest is not None:
-            skip_exceptions.append(unittest.SkipTest)
+            # Type ignored because unittest is loaded dynamically.
+            skip_exceptions.append(unittest.SkipTest)  # type: ignore
         if call.excinfo.errisinstance(tuple(skip_exceptions)):
             outcome = "skipped"
             r = collector._repr_failure_py(call.excinfo, "line").reprcrash
@@ -266,7 +276,7 @@ def pytest_make_collect_report(collector):
     rep = CollectReport(
         collector.nodeid, outcome, longrepr, getattr(call, "result", None)
     )
-    rep.call = call  # see collect_one_node
+    rep.call = call  # type: ignore # see collect_one_node
     return rep
 
 
@@ -274,8 +284,8 @@ class SetupState:
     """ shared state for setting up/tearing down test items or collectors. """
 
     def __init__(self):
-        self.stack = []
+        self.stack = []  # type: List[Node]
-        self._finalizers = {}
+        self._finalizers = {}  # type: Dict[Node, List[Callable[[], None]]]
 
     def addfinalizer(self, finalizer, colitem):
         """ attach a finalizer to the given colitem. """
@@ -302,6 +312,7 @@ class SetupState:
                     exc = sys.exc_info()
         if exc:
             _, val, tb = exc
+            assert val is not None
             raise val.with_traceback(tb)
 
     def _teardown_with_finalization(self, colitem):
@@ -335,6 +346,7 @@ class SetupState:
                     exc = sys.exc_info()
         if exc:
             _, val, tb = exc
+            assert val is not None
             raise val.with_traceback(tb)
 
     def prepare(self, colitem):