问题:将带有参数的函数传递给Python中的另一个函数?

是否可以将带有参数的函数传递给Python中的另一个函数?

说出类似的内容:

def perform(function):
    return function()

但是要传递的函数将具有以下参数:

action1()
action2(p)
action3(p,r)

Is it possible to pass functions with arguments to another function in Python?

Say for something like:

def perform(function):
    return function()

But the functions to be passed will have arguments like:

action1()
action2(p)
action3(p,r)

回答 0

你是这个意思吗

def perform( fun, *args ):
    fun( *args )

def action1( args ):
    something

def action2( args ):
    something

perform( action1 )
perform( action2, p )
perform( action3, p, r )

Do you mean this?

def perform( fun, *args ):
    fun( *args )

def action1( args ):
    something

def action2( args ):
    something

perform( action1 )
perform( action2, p )
perform( action3, p, r )

回答 1

这就是lambda的用途:

def Perform(f):
    f()

Perform(lambda: Action1())
Perform(lambda: Action2(p))
Perform(lambda: Action3(p, r))

This is what lambda is for:

def Perform(f):
    f()

Perform(lambda: Action1())
Perform(lambda: Action2(p))
Perform(lambda: Action3(p, r))

回答 2

您可以像这样从functools使用局部函数。

from functools import partial

def perform(f):
    f()

perform(Action1)
perform(partial(Action2, p))
perform(partial(Action3, p, r))

也适用于关键字

perform(partial(Action4, param1=p))

You can use the partial function from functools like so.

from functools import partial

def perform(f):
    f()

perform(Action1)
perform(partial(Action2, p))
perform(partial(Action3, p, r))

Also works with keywords

perform(partial(Action4, param1=p))

回答 3

使用functools.partial,而不是lambdas!而且Ofc Perform是一个无用的函数,您可以直接传递函数。

for func in [Action1, partial(Action2, p), partial(Action3, p, r)]:
  func()

Use functools.partial, not lambdas! And ofc Perform is a useless function, you can pass around functions directly.

for func in [Action1, partial(Action2, p), partial(Action3, p, r)]:
  func()

回答 4

(几个月后)一个很小的真实示例,其中lambda很有用,但部分没有用:
说您想要通过2维函数的各种1维横截面,例如穿过一排山丘的切片。
quadf( x, f )接受一维f并调用它x
称其为y = -1 0 1处的垂直切割和x = -1 0 1处的水平切割

fx1 = quadf( x, lambda x: f( x, 1 ))
fx0 = quadf( x, lambda x: f( x, 0 ))
fx_1 = quadf( x, lambda x: f( x, -1 ))
fxy = parabola( y, fx_1, fx0, fx1 )

f_1y = quadf( y, lambda y: f( -1, y ))
f0y = quadf( y, lambda y: f( 0, y ))
f1y = quadf( y, lambda y: f( 1, y ))
fyx = parabola( x, f_1y, f0y, f1y )

据我所知,partial不能这样做-

quadf( y, partial( f, x=1 ))
TypeError: f() got multiple values for keyword argument 'x'

(如何为此添加标签numpy,partial,lambda?)

(months later) a tiny real example where lambda is useful, partial not:
say you want various 1-dimensional cross-sections through a 2-dimensional function, like slices through a row of hills.
quadf( x, f ) takes a 1-d f and calls it for various x.
To call it for vertical cuts at y = -1 0 1 and horizontal cuts at x = -1 0 1,

fx1 = quadf( x, lambda x: f( x, 1 ))
fx0 = quadf( x, lambda x: f( x, 0 ))
fx_1 = quadf( x, lambda x: f( x, -1 ))
fxy = parabola( y, fx_1, fx0, fx1 )

f_1y = quadf( y, lambda y: f( -1, y ))
f0y = quadf( y, lambda y: f( 0, y ))
f1y = quadf( y, lambda y: f( 1, y ))
fyx = parabola( x, f_1y, f0y, f1y )

As far as I know, partial can’t do this —

quadf( y, partial( f, x=1 ))
TypeError: f() got multiple values for keyword argument 'x'

(How to add tags numpy, partial, lambda to this ?)


回答 5

这称为部分函数,​​至少有3种方法可以做到这一点。我最喜欢的方式是使用lambda,因为它避免了对额外程序包的依赖,并且最不冗长。假设您有一个函数,add(x, y)并且希望将add(3, y)其他函数作为参数传递,以便其他函数确定用于y

使用lambda

# generic function takes op and its argument
def runOp(op, val):
    return op(val)

# declare full function
def add(x, y):
    return x+y

# run example
def main():
    f = lambda y: add(3, y)
    result = runOp(f, 1) # is 4

创建自己的包装器

在这里,您需要创建一个返回部分函数的函数。这显然更加冗长。

# generic function takes op and its argument
def runOp(op, val):
    return op(val)

# declare full function
def add(x, y):
    return x+y

# declare partial function
def addPartial(x):
    def _wrapper(y):
        return add(x, y)
    return _wrapper

# run example
def main():
    f = addPartial(3)
    result = runOp(f, 1) # is 4

从functools使用部分

这几乎与lambda上面显示的相同。那我们为什么需要这个呢?有几个原因。简而言之,partial在某些情况下可能会更快(请参阅其实现),并且您可以将其用于早期绑定而不是lambda的后期绑定。

from functools import partial

# generic function takes op and its argument
def runOp(op, val):
    return op(val)

# declare full function
def add(x, y):
    return x+y

# run example
def main():
    f = partial(add, 3)
    result = runOp(f, 1) # is 4

This is called partial functions and there are at least 3 ways to do this. My favorite way is using lambda because it avoids dependency on extra package and is the least verbose. Assume you have a function add(x, y) and you want to pass add(3, y) to some other function as parameter such that the other function decides the value for y.

Use lambda

# generic function takes op and its argument
def runOp(op, val):
    return op(val)

# declare full function
def add(x, y):
    return x+y

# run example
def main():
    f = lambda y: add(3, y)
    result = runOp(f, 1) # is 4

Create Your Own Wrapper

Here you need to create a function that returns the partial function. This is obviously lot more verbose.

# generic function takes op and its argument
def runOp(op, val):
    return op(val)

# declare full function
def add(x, y):
    return x+y

# declare partial function
def addPartial(x):
    def _wrapper(y):
        return add(x, y)
    return _wrapper

# run example
def main():
    f = addPartial(3)
    result = runOp(f, 1) # is 4

Use partial from functools

This is almost identical to lambda shown above. Then why do we need this? There are few reasons. In short, partial might be bit faster in some cases (see its implementation) and that you can use it for early binding vs lambda’s late binding.

from functools import partial

# generic function takes op and its argument
def runOp(op, val):
    return op(val)

# declare full function
def add(x, y):
    return x+y

# run example
def main():
    f = partial(add, 3)
    result = runOp(f, 1) # is 4

回答 6

这是一种使用闭包的方法:

    def generate_add_mult_func(func):
        def function_generator(x):
            return reduce(func,range(1,x))
        return function_generator

    def add(x,y):
        return x+y

    def mult(x,y):
        return x*y

    adding=generate_add_mult_func(add)
    multiplying=generate_add_mult_func(mult)

    print adding(10)
    print multiplying(10)

Here is a way to do it with a closure:

    def generate_add_mult_func(func):
        def function_generator(x):
            return reduce(func,range(1,x))
        return function_generator

    def add(x,y):
        return x+y

    def mult(x,y):
        return x*y

    adding=generate_add_mult_func(add)
    multiplying=generate_add_mult_func(mult)

    print adding(10)
    print multiplying(10)

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