如何将一个函数作为参数传递给另一个函数，并在python中使用该函数返回的值？

Question

I am trying to negate the value returned by one function.

Consider the code to be

def greater(a,b):
    return a>b

check = negate(greater)

assert check(8,9)

OR

def equal(a,b):
    return a==b

check = negate(equal)

assert check("python","java")

How should I define the NEGATE function???

Answer 1

Use a function-style decorator :

def negate(func):
    def inner(*args, **kwargs):
        val = func(*args, **kwargs)
        return not val
    return inner

Demo:

>>> greater(10, 20)
False
>>> negate(greater)(10, 20)
True

To preserve things like docstring and other attributes of the function being passed to negate you can use functools.wraps .

from functools import wraps

def negate(func):
    @wraps(func)
    def inner(*args, **kwargs):
        val = func(*args, **kwargs)
        return not val
    return inner

Answer 2

Like this:

def negate(func):
  def result(*args):
    return not func(*args)
  return result

This is a function which creates a function which returns the result of invoking the original function and not ing it's return value, and then returning that function.

Answer 3

Use the not operator in a decorator:

from functools import wraps

def negate(func):
    @wraps(func)
    def wrapper(*args, **kw):
        return not func(*args, **kw)
    return wrapper

The above decorator returns a wrapper function that applies not to the return value of the wrapped function. The @functools.wraps() decorator in the above example is optional but makes sure the wrapper gains the docstring and other introspectable attributes from the original function, making it behave more closely like the wrapped function.

Demo:

>>> from functools import wraps
>>> def negate(func):
...     @wraps(func)
...     def wrapper(*args, **kw):
...         return not func(*args, **kw)
...     return wrapper
... 
>>> def greater(a,b):
...     return a>b
... 
>>> check = negate(greater)
>>> check(8, 9)
True