Question: Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

```
class Solution:
def twoSum(self, nums, target):

    lookup={}
    for cnt, num in enumerate (nums):
        if target-num in lookup:
            return lookup[target-num], cnt
        lookup[num]=cnt

```

I am not able to understand the steps after for loop is used.I am new on Python, someone please help me.