[1,2,3,4,3,2,1] 

 a = [1,2,3,4,3,2,1]
b = []
for i in a:
    b.append(str(i))
b = ''.join(b)

 b = ''.join(b)

 >>> a = [1,2,3,4,3,2,1]
>>> b = ''.join(map(str,a))
>>> b
'1234321'
>>>

 "".join([str(1),str(2)])
"".join([hex(1),hex(2)])

 "".concat(1,2,3)
"123"

  
>>> m = map(str, [1, 2, 3])
>>> m
<map object at 0x7fbe40fdfe80>
>>> dir(m)
['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__lt__', '__ne__', '__new__', '__next__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']
>>>
>>> next(m)
'1'
>>> next(m)
'2'
>>> next(m)
'3'
>>> next(m)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration
>>>