The main problem with callable type hints is that they can be misleading. For example, the following code snippet uses a callable type hint to indicate that the function f() should be treated as a function that takes one argument:
def f(x):
print(“In f() x is {}”.format(x))
However, this code actually defines a function that takes two arguments. If you try to run this code, you’ll get an error message like this:
In f() x is not defined
This error message is caused by the fact that Python doesn’t know how to interpret the callable type hint in this context. In general, callable type hints are only useful if you’re actually defining a function that takes one or more arguments.
def foo(x: callable[[int], int]) -> int:
return x(3)
#In this example, the foo function takes an argument x that must be a callable object,
#and returns an int. The callable object must take an int as its first argument
#and return an int.
#When the foo function is called, it will call the x function with 3 as its first argument.
#The return value of the x function will be returned by the foo function.
Type Hint
Type hinting is a feature of the Python programming language that allows you to indicate to the compiler which type of variable or function you are referring to.
What is typing
?
In Python, typing is the process of entering text on a computer keyboard.
