Add hints for most of the intermediate challenges (#74)

Author: piglei

challenges/intermediate-await/hints.md

@@ -0,0 +1 @@
+Check out [Awaitable](https://docs.python.org/3.12/library/collections.abc.html#collections.abc.Awaitable).

challenges/intermediate-await/solution.py

@@ -4,7 +4,7 @@
 `run_async` takes an awaitable integer.
 """
 
-from typing import Awaitable
+from collections.abc import Awaitable
 
 
 def run_async(func: Awaitable[int]):

challenges/intermediate-callable/hints.md

@@ -0,0 +1 @@
+Check out [Callable](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable).

challenges/intermediate-callable/solution.py

@@ -4,7 +4,7 @@
 Define a callable type that accepts a string argument and returns None.
 *The parameter name can be arbitrary.*
 """
-from typing import Callable
+from collections.abc import Callable
 
 SingleStringInput = Callable[[str], None]
 

challenges/intermediate-class-var/hints.md

@@ -0,0 +1 @@
+Check out [ClassVar](https://docs.python.org/3/library/typing.html#typing.ClassVar).

challenges/intermediate-decorator/hints.md

@@ -0,0 +1 @@
+[TypeVar](https://docs.python.org/3/library/typing.html#typing.TypeVar) and [Callable](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable) are all you need.

challenges/intermediate-generic/hints.md

@@ -0,0 +1,2 @@
+- Use [TypeVar](https://docs.python.org/3/library/typing.html#typing.TypeVar) to annotate a generic function.
+- Or try the ["Generic Functions"](https://docs.python.org/3/reference/compound_stmts.html#generic-functions) statement, it looks like this: `def func[T](arg: T): ...`.

challenges/intermediate-generic2/hints.md

@@ -1 +1,2 @@
-Check out [TypeVar](https://docs.python.org/3/library/typing.html#typing.TypeVar), the `constraints` argument might be a good fit for this challenge.
+- [TypeVar](https://docs.python.org/3/library/typing.html#typing.TypeVar) with `constraints` might be a good fit for this challenge.
+- You can also try to solve this using the ["Generic Functions"](https://docs.python.org/3/reference/compound_stmts.html#generic-functions) statement.

challenges/intermediate-instance-var/hints.md

@@ -0,0 +1 @@
+Annotating an instance variable is the same as annotating a variable, except that you have to put the code in the class body.

challenges/intermediate-literal/hints.md

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+Check out [Literal](https://docs.python.org/3/library/typing.html#typing.Literal).