插值lambda难以理解

Question

poly1 and poly2 are both lists containing coordinates (x,y).

Now this function is pre-implemented, which I find hard to understand:

def interpolate():
    # This function returns a list of tuples (x, y).
    return map(lambda a, b: (a[0] + b[0], a[1] + b[1]), poly_1,
               [(time * x[0], time * x[1]) for x in map(lambda p, q: (q[0] - p[0], q[1] - p[1]), poly_1, poly_2)])

But can you actually explain what happens in interpolate ?

All I can extract from this is (as far as the lambdas go)

def func_a(a, b):
    return (a[0] + b[0], a[1] + b[1])

and

def func_b(p, q):
    return (q[0] - p[0], q[1] - p[1]), poly_1, poly_2)

But all that mapping is confusing to me.

Answer 1

map simply apply a function to every element in one or more arrays

Lets take a look:

return map(lambda a, b: (a[0] + b[0], a[1] + b[1]), poly_1,
           [(time * x[0], time * x[1]) for x in map(lambda p, q: (q[0] - p[0], q[1] - p[1]), poly_1, poly_2)])

Its a map function that takes 3 arguments:

1. lambda a, b: (a[0] + b[0], a[1] + b[1]) can be translated as

def foo(a,b) : return (a[0] + b[0], a[1] + b[1])

You will apply it on next two lists

2. The first list poly_1

3. The second list [(time * x[0], time * x[1]) for x in map(lambda p, q: (q[0] - p[0], q[1] - p[1]), poly_1, poly_2)] :

First its a list of tuples with two arguments time * x[0], time * x[1]

"x" is taken from the list that return from map(lambda p, q: (q[0] - p[0], q[1] - p[1]), poly_1, poly_2)

Lets translate it:

1. map applies the lambda function to every element of poly_1 and poly_2
2. lambda p, q: (q[0] - p[0], q[1] - p[1]) equals to

def foo2(p,q) : return (q[0] - p[0], q[1] - p[1])

Answer 2

side note:

def interpolate(poly_1, poly_2):
    return map(lambda p, q: (p[0] + t*(q[0]-p[0]), p[1] + t*(q[1]-p[1])), poly_1, poly_2)

does the same job. way faster