Python incorrect ways to add to list when generating permutations

Question

In this example, why does this generate the correct result:

nxt = path + [nums[i]]

But not:

nxt = path ; nxt += [nums[i]]

nxt = path ; nxt.append(nums[i])

def permute(nums):
    def dfs(nums, path):
      if not nums: # empty, done with path
          all_perms.append(path)
          return

      for i in range(len(nums)):
        nxt = path + [nums[i]]
        # nxt = path ; nxt += [nums[i]]
        # nxt = path ; nxt.append(nums[i])
        print(nxt)
        dfs(nums[:i] + nums[i+1:], nxt)

    all_perms = []
    dfs(nums, [])
    return all_perms

Answer 1

In this example, why does this generate the correct result:

 nxt = path + [nums[i]]

This leaves path unmodified.

But not:

 nxt = path ; nxt += [nums[i]]

 nxt = path ; nxt.append(nums[i])

This appends nums[i] to path which is apparently incorrect.