diff --git a/mypy/plugins/default.py b/mypy/plugins/default.py
index b9ec575dabb5..ca9d3baad3bb 100644
--- a/mypy/plugins/default.py
+++ b/mypy/plugins/default.py
@@ -2,9 +2,10 @@
from typing import Callable, Optional, List
from mypy import message_registry
-from mypy.nodes import StrExpr, IntExpr, DictExpr, UnaryExpr
+from mypy.nodes import Expression, StrExpr, IntExpr, DictExpr, UnaryExpr
from mypy.plugin import (
- Plugin, FunctionContext, MethodContext, MethodSigContext, AttributeContext, ClassDefContext
+ Plugin, FunctionContext, MethodContext, MethodSigContext, AttributeContext, ClassDefContext,
+ CheckerPluginInterface,
)
from mypy.plugins.common import try_getting_str_literals
from mypy.types import (
@@ -66,6 +67,8 @@ def get_method_hook(self, fullname: str
return ctypes.array_getitem_callback
elif fullname == 'ctypes.Array.__iter__':
return ctypes.array_iter_callback
+ elif fullname == 'pathlib.Path.open':
+ return path_open_callback
return None
def get_attribute_hook(self, fullname: str
@@ -101,23 +104,55 @@ def get_class_decorator_hook(self, fullname: str
def open_callback(ctx: FunctionContext) -> Type:
- """Infer a better return type for 'open'.
-
- Infer TextIO or BinaryIO as the return value if the mode argument is not
- given or is a literal.
+ """Infer a better return type for 'open'."""
+ return _analyze_open_signature(
+ arg_types=ctx.arg_types,
+ args=ctx.args,
+ mode_arg_index=1,
+ default_return_type=ctx.default_return_type,
+ api=ctx.api,
+ )
+
+
+def path_open_callback(ctx: MethodContext) -> Type:
+ """Infer a better return type for 'pathlib.Path.open'."""
+ return _analyze_open_signature(
+ arg_types=ctx.arg_types,
+ args=ctx.args,
+ mode_arg_index=0,
+ default_return_type=ctx.default_return_type,
+ api=ctx.api,
+ )
+
+
+def _analyze_open_signature(arg_types: List[List[Type]],
+ args: List[List[Expression]],
+ mode_arg_index: int,
+ default_return_type: Type,
+ api: CheckerPluginInterface,
+ ) -> Type:
+ """A helper for analyzing any function that has approximately
+ the same signature as the builtin 'open(...)' function.
+
+ Currently, the only thing the caller can customize is the index
+ of the 'mode' argument. If the mode argument is omitted or is a
+ string literal, we refine the return type to either 'TextIO' or
+ 'BinaryIO' as appropriate.
"""
mode = None
- if not ctx.arg_types or len(ctx.arg_types[1]) != 1:
+ if not arg_types or len(arg_types[mode_arg_index]) != 1:
mode = 'r'
- elif isinstance(ctx.args[1][0], StrExpr):
- mode = ctx.args[1][0].value
+ else:
+ mode_expr = args[mode_arg_index][0]
+ if isinstance(mode_expr, StrExpr):
+ mode = mode_expr.value
if mode is not None:
- assert isinstance(ctx.default_return_type, Instance) # type: ignore
+ assert isinstance(default_return_type, Instance) # type: ignore
if 'b' in mode:
- return ctx.api.named_generic_type('typing.BinaryIO', [])
+ return api.named_generic_type('typing.BinaryIO', [])
else:
- return ctx.api.named_generic_type('typing.TextIO', [])
- return ctx.default_return_type
+ return api.named_generic_type('typing.TextIO', [])
+ return default_return_type
def contextmanager_callback(ctx: FunctionContext) -> Type:
diff --git a/test-data/unit/pythoneval.test b/test-data/unit/pythoneval.test
index 1a3c778b4604..f3a88ca47dcc 100644
--- a/test-data/unit/pythoneval.test
+++ b/test-data/unit/pythoneval.test
@@ -299,6 +299,32 @@ _testOpenReturnTypeInferenceSpecialCases.py:2: note: Revealed type is 'typing.Bi
_testOpenReturnTypeInferenceSpecialCases.py:3: note: Revealed type is 'typing.BinaryIO'
_testOpenReturnTypeInferenceSpecialCases.py:5: note: Revealed type is 'typing.IO[Any]'
+[case testPathOpenReturnTypeInference]
+from pathlib import Path
+p = Path("x")
+reveal_type(p.open())
+reveal_type(p.open('r'))
+reveal_type(p.open('rb'))
+mode = 'rb'
+reveal_type(p.open(mode))
+[out]
+_program.py:3: note: Revealed type is 'typing.TextIO'
+_program.py:4: note: Revealed type is 'typing.TextIO'
+_program.py:5: note: Revealed type is 'typing.BinaryIO'
+_program.py:7: note: Revealed type is 'typing.IO[Any]'
+
+[case testPathOpenReturnTypeInferenceSpecialCases]
+from pathlib import Path
+p = Path("x")
+reveal_type(p.open(mode='rb', errors='replace'))
+reveal_type(p.open(errors='replace', mode='rb'))
+mode = 'rb'
+reveal_type(p.open(mode=mode, errors='replace'))
+[out]
+_program.py:3: note: Revealed type is 'typing.BinaryIO'
+_program.py:4: note: Revealed type is 'typing.BinaryIO'
+_program.py:6: note: Revealed type is 'typing.IO[Any]'
+
[case testGenericPatterns]
from typing import Pattern
import re
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