fixes to dis stubs (#1025)

- Add sys.version_info checks (mypy now supports them)
- Went over Python 3 docs and corrected a few things
- Reexport things that are imported from opcode

stdlib/3/dis.pyi

@@ -3,48 +3,48 @@ from typing import List, Union, Iterator, Tuple, Optional, Any, IO, NamedTuple,
 import sys
 import types
 
-from opcode import (hasconst, hasname, hasjrel, hasjabs, haslocal, hascompare,
-                    hasfree, cmp_op, opname, opmap, HAVE_ARGUMENT,
-                    EXTENDED_ARG)
+from opcode import (hasconst as hasconst, hasname as hasname, hasjrel as hasjrel,
+                    hasjabs as hasjabs, haslocal as haslocal, hascompare as hascompare,
+                    hasfree as hasfree, cmp_op as cmp_op, opname as opname, opmap as opmap,
+                    HAVE_ARGUMENT as HAVE_ARGUMENT, EXTENDED_ARG as EXTENDED_ARG)
 
 if sys.version_info >= (3, 4):
-    from opcode import stack_effect
+    from opcode import stack_effect as stack_effect
 
 if sys.version_info >= (3, 6):
-    from opcode import hasnargs
+    from opcode import hasnargs as hasnargs
 
 _have_code = Union[types.MethodType, types.FunctionType, types.CodeType, type]
 _have_code_or_string = Union[_have_code, str, bytes]
 
 
-Instruction = NamedTuple(
-    "Instruction",
-    [
-        ('opname', str),
-        ('opcode', int),
-        ('arg', Optional[int]),
-        ('argval', Any),
-        ('argrepr', str),
-        ('offset', int),
-        ('starts_line', Optional[int]),
-        ('is_jump_target', bool)
-    ]
-)
+if sys.version_info >= (3, 4):
+    Instruction = NamedTuple(
+        "Instruction",
+        [
+            ('opname', str),
+            ('opcode', int),
+            ('arg', Optional[int]),
+            ('argval', Any),
+            ('argrepr', str),
+            ('offset', int),
+            ('starts_line', Optional[int]),
+            ('is_jump_target', bool)
+        ]
+    )
 
+    class Bytecode:
+        codeobj = ...  # type: types.CodeType
+        first_line = ...  # type: int
+        def __init__(self, x: _have_code_or_string, *, first_line: Optional[int] = ...,
+                     current_offset: Optional[int] = ...) -> None: ...
+        def __iter__(self) -> Iterator[Instruction]: ...
+        def __repr__(self) -> str: ...
+        def info(self) -> str: ...
+        def dis(self) -> str: ...
 
-# if sys.version_info >= (3, 4):
-class Bytecode:
-    codeobj = ...  # type: types.CodeType
-    first_line = ...  # type: int
-    def __init__(self, x: _have_code_or_string, *, first_line: int=...,
-                 current_offset: int=...) -> None: ...
-    def __iter__(self) -> Iterator[Instruction]: ...
-    def __repr__(self) -> str: ...
-    def info(self) -> str: ...
-    def dis(self) -> str: ...
-
-    @classmethod
-    def from_traceback(cls, tb: types.TracebackType) -> Bytecode: ...
+        @classmethod
+        def from_traceback(cls, tb: types.TracebackType) -> Bytecode: ...
 
 
 COMPILER_FLAG_NAMES = ...  # type:  Dict[int, str]
@@ -54,17 +54,19 @@ def pretty_flags(flags: int) -> str: ...
 def findlabels(code: _have_code) -> List[int]: ...
 def findlinestarts(code: _have_code) -> Iterator[Tuple[int, int]]: ...
 
-# Signature changes are not allowed by mypy
-# 'All conditional function variants must have identical signatures'
-# TODO: mypy issue #698
-
-# if sys.version_info >= (3, 2):
 def code_info(x: _have_code_or_string) -> str: ...
 
-# `file` parameter requires sys.version_info >= (3, 4):
-def dis(x: _have_code_or_string = ..., *, file: IO[str] = None) -> None: ...
-def distb(tb: types.TracebackType = ..., *, file: IO[str] = None) -> None: ...
-def disassemble(co: _have_code, lasti: int = ..., *, file: IO[str] = None) -> None: ...
-def show_code(co: _have_code, *, file: IO[str] = None) -> None: ...
+if sys.version_info >= (3, 4):
+    def dis(x: _have_code_or_string = ..., *, file: Optional[IO[str]] = ...) -> None: ...
+    def distb(tb: Optional[types.TracebackType] = ..., *, file: Optional[IO[str]] = ...) -> None: ...
+    def disassemble(co: _have_code, lasti: int = ..., *, file: Optional[IO[str]] = ...) -> None: ...
+    def disco(co: _have_code, lasti: int = ..., *, file: Optional[IO[str]] = ...) -> None: ...
+    def show_code(co: _have_code, *, file: Optional[IO[str]] = ...) -> None: ...
 
-def get_instructions(x: _have_code, *, first_line: int = ...) -> Iterator[Instruction]: ...
+    def get_instructions(x: _have_code, *, first_line: Optional[int] = ...) -> Iterator[Instruction]: ...
+else:
+    def dis(x: _have_code_or_string = ...) -> None: ...
+    def distb(tb: types.TracebackType = ...) -> None: ...
+    def disassemble(co: _have_code, lasti: int = ...) -> None: ...
+    def disco(co: _have_code, lasti: int = ...) -> None: ...
+    def show_code(co: _have_code) -> None: ...