[clean strict optional] Fix some strict optional errors in mypy (#3228)

This PR fixes 26 ``--strict-optional`` errors in mypy itself (out of 547 total) in following files:
* stubgen.py
* stubgenc.py
* checkstrformat.py
* report.py
* strconv.py

Author: ilevkivskyi

mypy/checkstrformat.py

@@ -2,7 +2,7 @@
 
 import re
 
-from typing import cast, List, Tuple, Dict, Callable, Union
+from typing import cast, List, Tuple, Dict, Callable, Union, Optional
 
 from mypy.types import (
     Type, AnyType, TupleType, Instance, UnionType
@@ -18,6 +18,7 @@
 from mypy.messages import MessageBuilder
 
 FormatStringExpr = Union[StrExpr, BytesExpr, UnicodeExpr]
+Checkers = Tuple[Callable[[Expression], None], Callable[[Type], None]]
 
 
 class ConversionSpecifier:
@@ -105,7 +106,7 @@ def parse_conversion_specifiers(self, format: str) -> List[ConversionSpecifier]:
         return specifiers
 
     def analyze_conversion_specifiers(self, specifiers: List[ConversionSpecifier],
-                                      context: Context) -> bool:
+                                      context: Context) -> Optional[bool]:
         has_star = any(specifier.has_star() for specifier in specifiers)
         has_key = any(specifier.has_key() for specifier in specifiers)
         all_have_keys = all(
@@ -192,9 +193,8 @@ def check_mapping_str_interpolation(self, specifiers: List[ConversionSpecifier],
 
     def build_replacement_checkers(self, specifiers: List[ConversionSpecifier],
                                    context: Context, expr: FormatStringExpr
-                                   ) -> List[Tuple[Callable[[Expression], None],
-                                                   Callable[[Type], None]]]:
-        checkers = []  # type: List[Tuple[Callable[[Expression], None], Callable[[Type], None]]]
+                                   ) -> Optional[List[Checkers]]:
+        checkers = []  # type: List[Checkers]
         for specifier in specifiers:
             checker = self.replacement_checkers(specifier, context, expr)
             if checker is None:
@@ -203,13 +203,12 @@ def build_replacement_checkers(self, specifiers: List[ConversionSpecifier],
         return checkers
 
     def replacement_checkers(self, specifier: ConversionSpecifier, context: Context,
-                             expr: FormatStringExpr) -> List[Tuple[Callable[[Expression], None],
-                                                                   Callable[[Type], None]]]:
+                             expr: FormatStringExpr) -> Optional[List[Checkers]]:
         """Returns a list of tuples of two functions that check whether a replacement is
         of the right type for the specifier. The first functions take a node and checks
         its type in the right type context. The second function just checks a type.
         """
-        checkers = []  # type: List[Tuple[Callable[[Expression], None], Callable[[Type], None]]]
+        checkers = []  # type: List[Checkers]
 
         if specifier.width == '*':
             checkers.append(self.checkers_for_star(context))
@@ -227,14 +226,13 @@ def replacement_checkers(self, specifier: ConversionSpecifier, context: Context,
             checkers.append(c)
         return checkers
 
-    def checkers_for_star(self, context: Context) -> Tuple[Callable[[Expression], None],
-                                                           Callable[[Type], None]]:
+    def checkers_for_star(self, context: Context) -> Checkers:
         """Returns a tuple of check functions that check whether, respectively,
         a node or a type is compatible with a star in a conversion specifier
         """
         expected = self.named_type('builtins.int')
 
-        def check_type(type: Type = None) -> None:
+        def check_type(type: Type) -> None:
             expected = self.named_type('builtins.int')
             self.chk.check_subtype(type, expected, context, '* wants int')
 
@@ -246,16 +244,16 @@ def check_expr(expr: Expression) -> None:
 
     def checkers_for_regular_type(self, type: str,
                                   context: Context,
-                                  expr: FormatStringExpr) -> Tuple[Callable[[Expression], None],
-                                                                   Callable[[Type], None]]:
+                                  expr: FormatStringExpr) -> Optional[Checkers]:
         """Returns a tuple of check functions that check whether, respectively,
         a node or a type is compatible with 'type'. Return None in case of an
         """
         expected_type = self.conversion_type(type, context, expr)
         if expected_type is None:
             return None
 
-        def check_type(type: Type = None) -> None:
+        def check_type(type: Type) -> None:
+            assert expected_type is not None
             self.chk.check_subtype(type, expected_type, context,
                               messages.INCOMPATIBLE_TYPES_IN_STR_INTERPOLATION,
                               'expression has type', 'placeholder has type')
@@ -268,16 +266,16 @@ def check_expr(expr: Expression) -> None:
 
     def checkers_for_c_type(self, type: str,
                             context: Context,
-                            expr: FormatStringExpr) -> Tuple[Callable[[Expression], None],
-                                                             Callable[[Type], None]]:
+                            expr: FormatStringExpr) -> Optional[Checkers]:
         """Returns a tuple of check functions that check whether, respectively,
         a node or a type is compatible with 'type' that is a character type
         """
         expected_type = self.conversion_type(type, context, expr)
         if expected_type is None:
             return None
 
-        def check_type(type: Type = None) -> None:
+        def check_type(type: Type) -> None:
+            assert expected_type is not None
             self.chk.check_subtype(type, expected_type, context,
                               messages.INCOMPATIBLE_TYPES_IN_STR_INTERPOLATION,
                               'expression has type', 'placeholder has type')
@@ -291,7 +289,7 @@ def check_expr(expr: Expression) -> None:
 
         return check_expr, check_type
 
-    def conversion_type(self, p: str, context: Context, expr: FormatStringExpr) -> Type:
+    def conversion_type(self, p: str, context: Context, expr: FormatStringExpr) -> Optional[Type]:
         """Return the type that is accepted for a string interpolation
         conversion specifier type.
 

mypy/parse.py

@@ -7,7 +7,7 @@
 
 def parse(source: Union[str, bytes],
           fnam: str,
-          errors: Errors,
+          errors: Optional[Errors],
           options: Options) -> MypyFile:
     """Parse a source file, without doing any semantic analysis.
 

mypy/report.py

@@ -200,7 +200,7 @@ def visit_func_def(self, defn: FuncDef) -> None:
             if cur_indent is None:
                 # Consume the line, but don't mark it as belonging to the function yet.
                 cur_line += 1
-            elif cur_indent > start_indent:
+            elif start_indent is not None and cur_indent > start_indent:
                 # A non-blank line that belongs to the function.
                 cur_line += 1
                 end_line = cur_line
@@ -211,7 +211,7 @@ def visit_func_def(self, defn: FuncDef) -> None:
         is_typed = defn.type is not None
         for line in range(start_line, end_line):
             old_indent, _ = self.lines_covered[line]
-            assert start_indent > old_indent
+            assert start_indent is not None and start_indent > old_indent
             self.lines_covered[line] = (start_indent, is_typed)
 
         # Visit the body, in case there are nested functions
@@ -304,7 +304,7 @@ def __init__(self, reports: Reports, output_dir: str) -> None:
         self.css_html_path = os.path.join(reports.data_dir, 'xml', 'mypy-html.css')
         xsd_path = os.path.join(reports.data_dir, 'xml', 'mypy.xsd')
         self.schema = etree.XMLSchema(etree.parse(xsd_path))
-        self.last_xml = None  # type: etree._ElementTree
+        self.last_xml = None  # type: Optional[etree._ElementTree]
         self.files = []  # type: List[FileInfo]
 
     def on_file(self,
@@ -532,6 +532,7 @@ def on_file(self,
 
     def on_finish(self) -> None:
         last_xml = self.memory_xml.last_xml
+        assert last_xml is not None
         out_path = os.path.join(self.output_dir, 'index.xml')
         out_xslt = os.path.join(self.output_dir, 'mypy-html.xslt')
         out_css = os.path.join(self.output_dir, 'mypy-html.css')
@@ -575,6 +576,7 @@ def on_file(self,
 
     def on_finish(self) -> None:
         last_xml = self.memory_xml.last_xml
+        assert last_xml is not None
         out_path = os.path.join(self.output_dir, 'index.html')
         out_css = os.path.join(self.output_dir, 'mypy-html.css')
         transformed_html = bytes(self.xslt_html(last_xml, ext=self.param_html))
@@ -606,6 +608,7 @@ def on_file(self,
 
     def on_finish(self) -> None:
         last_xml = self.memory_xml.last_xml
+        assert last_xml is not None
         out_path = os.path.join(self.output_dir, 'index.txt')
         stats.ensure_dir_exists(os.path.dirname(out_path))
         transformed_txt = bytes(self.xslt_txt(last_xml))

mypy/strconv.py

@@ -24,13 +24,14 @@ class StrConv(NodeVisitor[str]):
 
     def __init__(self, show_ids: bool = False) -> None:
         self.show_ids = show_ids
+        self.id_mapper = None  # type: Optional[IdMapper]
         if show_ids:
             self.id_mapper = IdMapper()
-        else:
-            self.id_mapper = None
 
-    def get_id(self, o: object) -> int:
-        return self.id_mapper.id(o)
+    def get_id(self, o: object) -> Optional[int]:
+        if self.id_mapper:
+            return self.id_mapper.id(o)
+        return None
 
     def format_id(self, o: object) -> str:
         if self.id_mapper:
@@ -47,6 +48,7 @@ def dump(self, nodes: Sequence[object], obj: 'mypy.nodes.Context') -> str:
         """
         tag = short_type(obj) + ':' + str(obj.get_line())
         if self.show_ids:
+            assert self.id_mapper is not None
             tag += '<{}>'.format(self.get_id(obj))
         return dump_tagged(nodes, tag, self)
 
@@ -504,7 +506,7 @@ def visit_backquote_expr(self, o: 'mypy.nodes.BackquoteExpr') -> str:
         return self.dump([o.expr], o)
 
 
-def dump_tagged(nodes: Sequence[object], tag: str, str_conv: 'StrConv') -> str:
+def dump_tagged(nodes: Sequence[object], tag: Optional[str], str_conv: 'StrConv') -> str:
     """Convert an array into a pretty-printed multiline string representation.
 
     The format is

mypy/stubgen.py

@@ -311,11 +311,10 @@ def visit_decorator(self, o: Decorator) -> None:
         super().visit_decorator(o)
 
     def visit_class_def(self, o: ClassDef) -> None:
+        sep = None  # type: Optional[int]
         if not self._indent and self._state != EMPTY:
             sep = len(self._output)
             self.add('\n')
-        else:
-            sep = None
         self.add('%sclass %s' % (self._indent, o.name))
         self.record_name(o.name)
         base_types = self.get_base_types(o)
@@ -465,7 +464,7 @@ def visit_import(self, o: Import) -> None:
                 self.add_import_line('import %s as %s\n' % (id, target_name))
                 self.record_name(target_name)
 
-    def get_init(self, lvalue: str, rvalue: Expression) -> str:
+    def get_init(self, lvalue: str, rvalue: Expression) -> Optional[str]:
         """Return initializer for a variable.
 
         Return None if we've generated one already or if the variable is internal.
@@ -511,7 +510,9 @@ def output(self) -> str:
     def is_not_in_all(self, name: str) -> bool:
         if self.is_private_name(name):
             return False
-        return self.is_top_level() and bool(self._all_) and name not in self._all_
+        if self._all_:
+            return self.is_top_level() and name not in self._all_
+        return False
 
     def is_private_name(self, name: str) -> bool:
         return name.startswith('_') and (not name.endswith('__')

mypy/stubgenc.py

@@ -111,12 +111,15 @@ def generate_c_function_stub(module: ModuleType,
         self_arg = '%s, ' % self_var
     else:
         self_arg = ''
-    if name in ('__new__', '__init__') and name not in sigs and class_name in class_sigs:
+    if (name in ('__new__', '__init__') and name not in sigs and class_name and
+            class_name in class_sigs):
         sig = class_sigs[class_name]
     else:
         docstr = getattr(obj, '__doc__', None)
-        sig = infer_sig_from_docstring(docstr, name)
-        if not sig:
+        inferred = infer_sig_from_docstring(docstr, name)
+        if inferred:
+            sig = inferred
+        else:
             if class_name and name not in sigs:
                 sig = infer_method_sig(name)
             else:

mypy/stubutil.py

@@ -90,7 +90,8 @@ def is_c_module(module: ModuleType) -> bool:
     return '__file__' not in module.__dict__ or module.__dict__['__file__'].endswith('.so')
 
 
-def write_header(file: IO[str], module_name: str, pyversion: Tuple[int, int] = (3, 5)) -> None:
+def write_header(file: IO[str], module_name: Optional[str] = None,
+                 pyversion: Tuple[int, int] = (3, 5)) -> None:
     if module_name:
         if pyversion[0] >= 3:
             version = '%d.%d' % (sys.version_info.major,