Prevent TypedDict from accepting arbitrary parameters-CodePudding

I noticed that TypedDict seems to let you pass any arguments to it which is not great.

class X(TypedDict):
    id: int

obj1 = X(id=4)
print(obj1)
# {'obj1': 1}

obj2 = X(id=4, thing=3)
print(obj2)
# {'obj1': 1, 'thing': 3} # bad!

I guess this is since TypedDict only works at the type checker level.

But if I still wanted to prevent this happening during runtime, what is the alternative to using a TypedDict?

CodePudding user response：

It is possible to use mypy package.

sudo pip3.9 install mypy
rehash

cat typedDict_ex.py
#!/usr/bin/python3.9
from typing import TypedDict
class X(TypedDict):
    id: int

obj1 = X(id=4)
print(obj1)
# {'obj1': 1}

obj2 = X(id=4, thing=3)
print(obj2)
# {'obj1': 1, 'thing': 3} # bad!

mypy typedDict_ex.py
typedDict_ex.py:10: error: Extra key "thing" for TypedDict "X"
Found 1 error in 1 file (checked 1 source file)

CodePudding user response：

Type safety in current versions of Python is not achieved at runtime, but through the use of a static ahead-of-execution analysis with mypy

This is true also for dataclasses, which have a similar scope as TypedDict.

If you want to enforce type safety at runtime, this must be done explicitly, e.g.:

class Foo:
   def __init__(self, *, bar):
       if isinstance(bar, int):
           self.bar = bar
       else:
           raise TypeError

Foo(bar=1)
# <__main__.Foo at 0x7f5400f5c730>

Foo(bar="1")
# TypeError

Foo(baz=1)
# TypeError

or similar.