TypeError: ‘type‘ object is not iterable

Description of the problem: TypeError: 'type' object is not iterable occurs when python3 passes list in the def function

My list is obtained in the following way, value_list is some elements in the obtained set, which is actually a list too.

But passing the list into a def will report an error. Because it is traversed directly with for i in value_list: in this form, an error will be reported if this form is found.

 

But in the function changed to

def str_join(str_list): # The input is a list, and all the elements in the set are directly spliced ​​together and returned.
    l_result = ""
    it = iter(str_list)
    for l in it:
        l_result = l_result + l
    return l_result

This is not wrong.

But if you don't use the def function to pass in the list, but directly after fetching the set, directly for i in value_list: this will not report an error.