Python将带有参数的函数作为参数传递给高阶函数？

Question

When ever I try to pass one function with parameter (test) to a function (await_char) the passod on function executes first skipping the runtime order of await_char ?

`

def await_char(param, func="", msg=""):
    import keyboard
    if msg == "":
        msg_out = 'Press {} to continue'.format(param.upper())
    else:
        msg_out = msg
    print(msg_out)
    while True:
        if keyboard.is_pressed("c"):
            break
        if keyboard.is_pressed("C"):
            break
        if keyboard.is_pressed(param):
            if func:
                func()
            break


def test(msg):
    print(msg)


await_char("y", "press some button, like: Y", test("John"))

`

I tried args, kwargs but I don't know how to make this optional parameter

Answer 1

Typically when you pass arguments to a function, those arguments are evaluated when the function is called. In your case, you want a pointer to a function that will be called later. There are a few ways to do this, but the simplest and first that comes to mind is via the lambda operator. It allows you to create a nameless function and then use that unnamed function later. But, more than that, when you define the unnamed function, you can pass whatever arguments you want to at the time of definition.

So, simplest change to your code is to change:

await_char("y", "press some button, like: Y", test("John"))

to:

await_char("y", "press some button, like: Y", lambda: test("John"))

Also, as a side note, please be consistent with your argument order. You define:

def await_char(param, func="", msg="")

but then later call it via await_char(param, msg, func) more or less... The order must be maintained, or you will get unexpected results.

Also, as a matter of taste, func="" is not the best default choice. Typically for a variable like func , None would be a more common default value. "" for msg is a fine choice.