# 列表为可迭代对象
list_1 = ["1","2","3","4"]  # 元素为字符串的列表
res = "".join(list_1)    # res的值为 "1234",数据类型为str

# 字典为可迭代对象
dict_1 = {"key1":"value2","key2":"value2"} # key为字符串类型的字段
res = "".join(dict_1)    # res的值为"key1key2",数据类型为str

# 自己写一个可迭代的对象
class A:
  __field = []

  def __init__(self, *args):
    for i in args:
      self.__field.append(i)

  def __iter__(self):
    changdu = len(self.__field)
    for i in range(self.__index, changdu):
      yield self.__field[i]

a = A("1","2","3","4")
res = "".join(a)     # res的值为"1234",数据类型为str

# 比如 "--".join(list_1)这个操作,它的输出为"1--2--3--4",一个字符串
list_1 = ["1","2","3","4"]
param = "--"
res = ""
for i in range(len(list_1)):
  if i == len(lis) - 1:
    res += lis[i]
  else:
    res += lis[i]
    res += param
print(res)  # 输出为 "1--2--3--4"

# 那么字典，还有对象a呢？
print(list(dict_1))  # 输出 ["key1","key2"]
print(list(a))    # 输出 ["1","2","3","4"]

"||".join(["a","b","c"])  # 输出 "a||b||c"，类型为str
b"||".join([b"a", b"b", b"c"]) # 输出 b"a||b||c",类型为bytes类型

list_2 = ["1","2",3,4] # 列表中的元素由str类型，int类型
"".join(list_2)