From 3c804594214c7a3916d8183fa11dff1c77bae4a5 Mon Sep 17 00:00:00 2001
From: hauntsaninja <hauntsaninja@gmail.com>
Date: Mon, 1 May 2023 21:30:18 -0700
Subject: [PATCH 1/2] Improve assert_type phrasing
I'd like to make the fact that this does nothing at runtime
really obvious, since I suspect this is unintuitive for users who are
unfamiliar with static type checking.
I thought of this because of
https://discuss.python.org/t/add-arg-check-type-to-types/26384
wherein I'm skeptical that the user really did want `assert_type`.
---
Doc/library/typing.rst | 7 ++++---
Lib/typing.py | 7 ++++---
2 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/Doc/library/typing.rst b/Doc/library/typing.rst
index 409a95d528b5d3..c22fc0b28a50d0 100644
--- a/Doc/library/typing.rst
+++ b/Doc/library/typing.rst
@@ -2484,15 +2484,16 @@ Functions and decorators
Ask a static type checker to confirm that *val* has an inferred type of *typ*.
- When the type checker encounters a call to ``assert_type()``, it
+ At runtime this does nothing: it returns the first argument unchanged with no
+ checks or side effects, no matter the actual type of the argument.
+
+ When a static type checker encounters a call to ``assert_type()``, it
emits an error if the value is not of the specified type::
def greet(name: str) -> None:
assert_type(name, str) # OK, inferred type of `name` is `str`
assert_type(name, int) # type checker error
- At runtime this returns the first argument unchanged with no side effects.
-
This function is useful for ensuring the type checker's understanding of a
script is in line with the developer's intentions::
diff --git a/Lib/typing.py b/Lib/typing.py
index 354bc80eb3abfa..40ac7e9132da81 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -2308,15 +2308,16 @@ def cast(typ, val):
def assert_type(val, typ, /):
"""Ask a static type checker to confirm that the value is of the given type.
- When the type checker encounters a call to assert_type(), it
+ At runtime this does nothing: it returns the first argument unchanged with no
+ checks or side effects, no matter the actual type of the argument.
+
+ When a static type checker encounters a call to assert_type(), it
emits an error if the value is not of the specified type::
def greet(name: str) -> None:
assert_type(name, str) # ok
assert_type(name, int) # type checker error
- At runtime this returns the first argument unchanged and otherwise
- does nothing.
"""
return val
From 9376fbaf7dd0c451b0241129747ff5ea330f070b Mon Sep 17 00:00:00 2001
From: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
Date: Mon, 1 May 2023 21:44:04 -0700
Subject: [PATCH 2/2] Update Lib/typing.py
Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
---
Lib/typing.py | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Lib/typing.py b/Lib/typing.py
index 40ac7e9132da81..e743d8ab39d2ea 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -2309,7 +2309,7 @@ def assert_type(val, typ, /):
"""Ask a static type checker to confirm that the value is of the given type.
At runtime this does nothing: it returns the first argument unchanged with no
- checks or side effects, no matter the actual type of the argument.
+ checks or side effects, no matter the actual type of the argument.
When a static type checker encounters a call to assert_type(), it
emits an error if the value is not of the specified type::