如何使用 yield 将两个列表中的数字按索引连接到一个元组中？（Python）

Question

I need to make a "generator function" which will take 2 lists and concatenate numbres from two lists by indices into a tuple. For example:

l1 = [3, 2, 1]
l2 = [4, 3, 2]

The result of the first iteration will be (3, 4) The result of the second iteration will be (2, 3) And the third (1, 2) And also, one of lists may have more numbers than the other one. In that case I need to write condition "if one of the lists ended while iterating, then no further iterations are performed." (using try, except )

I know, that generator functions use yield instead of return , but I have no idea how to write this fuction... I did this

def generate_something(l1, l2):
    l3 = tuple(tuple(x) for x in zip(l1, l2))
    return l3

output is

((3, 4), (2, 3), (1, 2))

It works, but this is not geterator function, there is no yield , there is no first-,second-,etc- iterations. I hope you can help me...

Answer 1

May be this help for you:

def generate_something_2(l1, l2):
    # if one of the lists ended while iterating, then no further iterations are performed.
    # For this get minimal len of list
    min_i = len(l1) if len(l1) < len(l2) else len(l2)
    for i in range(0,min_i):
        yield (l1[i], l2[i])

l1 = [3, 2, 1, 1]
l2 = [4, 3, 2]

l3 = tuple(generate_something_2(l1, l2))
# Result: ((3, 4), (2, 3), (1, 2))
print(l3)

Answer 2

you can create your own generator:

def iterate_lists(l1,l2):
   for i,item in enumerate(l1):
       yield l1[i],l2[i]

or as a variable by generator comprehension :

iterate_lists = (li[i],l2[i] for i,item in enumerate(l1))

about if the lengthes arent equal its not clear to me what exactly you want to do, without the message you can just go on the smaller list... just change the for i,item in enumerate(l1) with for i in range(min((len(l1),len(l2)))

Answer 3

Use a while loop and keep track of the index position, when a IndexError is raised you've hit the end of the shortest list and stop:

def generate_something(l1, l2):
    idx = 0
    while True:
        try:
            yield l1[idx], l2[idx]
            idx += 1
        except IndexError:
            break


l1 = [3, 2, 1]
l2 = [4, 3, 2]

g = generate_something(l1, l2)
print(list(g))

Output:

[(3, 4), (2, 3), (1, 2)]