以字符串形式存储到运行的方法中的方法[重复]

Question

我有一本这样的字典：

dictionary = { "a":function_1(), "b":function_2(), "c":function_3()}

但由于我不想在声明字典时运行所有函数，所以我将它们存储为字符串：

dictionary = { "a":"function_1()", "b":"function_2()", "c":"function_3()"}

我想做的是根据与之关联的键只调用一个函数：

for key,value in dictionary.items():
     if key == something:
          wanted_variable = value

如果我现在打印 Wanted_variable，它将返回“function_1()”，我希望它是 function_1() 返回的内容...

谁能帮帮我？

Answer 1

由于函数是第一类对象，您可以在不调用它们的情况下传递对它们的引用，并在以后调用它们：

dictionary = {
    "a":function_1,  # No parens here anymore
    "b":function_2,  # ''
    "c":function_3,  # ''
}

for key,value in dictionary.items():
     if key == something:
          # "Calling" parens here, not in the dictionary values
          wanted_variable = value()   

或者，

dictionary = {
    "a":function_1,  # No parens here anymore
    "b":function_2,  # ''
    "c":function_3,  # ''
}

func = dictionary.get(key)
if func:
    wanted_variable = func()

最终会做同样的事情，但不必遍历字典项。

对于更复杂的场景，当你想要捕获一个未调用的函数但也该函数的参数时，还有functools.partial

from functools import partial

dictionary = {
    "a":partial(function_1, 123), 
    "b":partial(function_2, 456), 
    "c":partial(function_3, 789),
}

for key,value in dictionary.items():
     if key == something:
          # "Calling" parens here, not in the dictionary values
          # This will actually call, for example, function_1(123).
          wanted_variable = value()   

例如：

from functools import partial

def foo(x):
    print("x is", x)

wrapped_foo = partial(foo, 123)

# Pass wrapped_foo around however you want...
d = {'func': wrapped_foo}

# Call it later
d['func']()   # Prints "foo is 123"

Answer 2

无需调用即可存储函数：

dictionary = { "a":function_1, "b":function_2, "c":function_3}  # no ()

然后

for key, value in dictionary.items():
    if key == something:
        wanted_variable = value()

顺便说一句，还有更有效的获取wanted_variable的方法：

if something in dictionary:
    wanted_variable = dictionary[something]()

Answer 3

你需要用函数名来定义字典：

dictionary = {"a":function_1, "b":function_2, "c":function_3}

如果你在函数名后面加上括号，你会立即调用它。

调用需要的函数匹配为：

for key, value in dictionary.items():
     if key == 'a':
          wanted_variable = value()

Answer 4

你可以只存储函数而不调用它们：

dictionary = { "a":function_1, "b":function_2, "c":function_3}

然后：

for key,value in dictionary.items():
     if key == something:
          wanted_variable = value()

Answer 5

你可以存储不带 () 的函数，这样它们就不会执行，那么你可以这样做：

def func1():
   x = "func1"
   print(x)
   return x
def func2():
   x = "func2"
   print(x)
   return x


d = {"a":func1, "b":func2}

wanted_variable = d["a"]()

Answer 6

eval 是对您的这个问题的更简单和实际的答案。

dictionary = { "a":"function_1()", "b":"function_2()", "c":"function_3()"}

for key, value in dictionary.items():
    if key == something:
        wanted_variable = eval(value)