Python内置函数之callable函数解读

callable(object) -> bool

def add(a, b):
    return a + b

class Calculator:
    def multiply(self, a, b):
        return a * b

print(callable(add))           # 输出: True
print(callable(Calculator().multiply))  # 输出: True

print(callable(Calculator))    # 输出: True
obj = Calculator()             # 类被调用，创建实例

class Adder:
    def __call__(self, a, b):
        return a + b

adder = Adder()
print(callable(adder))         # 输出: True
print(adder(3, 4))             # 输出: 7（实例被调用）

print(callable(len))           # 输出: True

x = 42
s = "hello"
print(callable(x))             # 输出: False
print(callable(s))             # 输出: False

lst = [1, 2, 3]
dct = {"a": 1}
print(callable(lst))           # 输出: False
print(callable(dct.get))       # 输出: True（get是方法，可调用）

import math
print(callable(math))          # 输出: False
print(callable(math.sqrt))     # 输出: True

def apply_function(func, x):
    if not callable(func):
        raise TypeError("func必须是可调用对象")
    return func(x)

result = apply_function(lambda x: x**2, 5)  # 正常
# apply_function(42, 5)  # 报错：TypeError

def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

operation = add if True else subtract
print(callable(operation))     # 输出: True
print(operation(5, 3))         # 输出: 8

class EventHandler:
    def __init__(self, callback=None):
        self.callback = callback if callable(callback) else lambda x: None
    
    def handle_event(self, data):
        self.callback(data)

# 使用自定义回调
def log_data(data):
    print(f"Logging: {data}")

handler = EventHandler(log_data)
handler.handle_event("Event occurred")  # 输出: Logging: Event occurred

# 使用默认回调（无操作）
handler = EventHandler()
handler.handle_event("Silent event")    # 无输出

def ensure_callable(func):
    if not callable(func):
        raise ValueError("传入的不是可调用对象")
    
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__}...")
        return func(*args, **kwargs)
    
    return wrapper

@ensure_callable
def greet(name):
    return f"Hello, {name}!"

print(greet("Alice"))  # 输出: Calling greet... \n Hello, Alice!

class BadCallable:
    def __call__(self):
        raise Exception("Cannot be called")

obj = BadCallable()
print(callable(obj))  # 输出: True
# obj()  # 报错：Exception