python lambda evaluate expression-CodePudding

I am trying out lambda in python and came across this question:

def foo(y):
    return lambda x: x(x(y))
def bar(x):
    return lambda y: x(y)
print((bar)(bar)(foo)(2)(lambda x:x 1))

can someone explain/breakdown how this code works? I am having problems trying to figure out what is x and y.

CodePudding user response：

Lambda (in python) is just syntatic sugar. You can think of this structure:

anony_mouse = lambda x: x # don't actually assign lambdas

as equivalent to this structure:

def anony_mouse(x):
    return x

Thus let's write out the top example using standard function notation:

def foo(y):
    # note that y exists here
    def baz(x):
        return x(x(y))

    return baz

So we have a factory function, which generates a function which... expects to be called with a function (x), and returns x(x(arg_to_factory_function)). Consider:

>>> def add_six(x):
        return x   6
>>> bazzer = foo(3)
>>> bazzer(add_six) # add_six(add_six(3)) = 6 (6 3)

I could go on, but does that make it clearer?

Incidentally that code is horrible, and almost makes me agree with Guido that lambdas are bad.

CodePudding user response：

The 1st ‘(bar)’ is equal to just ‘bar’ so it is an ordinary function call, the 2nd — argument to that call, i.e. bar(bar) — substitute ‘x’ to ‘bar’ there any you will get what is result of bar(bar); the’(foo)’ argument passing to the result of bar(bar) it will be a lambda-function with some arg. — substitute it to ‘foo’ and get result and so on until you reach the end of expression