What I'm trying to do is to print the reverse number of the input. input = "1 3 4 2" output = "2 4 3 1"
I want to know why my code show this error:
if __name__ == "__main__":
n = 4
arr = map(int, "1 3 4 2".split())
ar = list(arr)
ar.reverse()
string = ' '
string.join(ar)
print(string)
Error:
string.join(ar)
TypeError: sequence item 0: expected str instance, int found
and if i change the map argument from int to str, it shows no result.
You should use much simpler approach:
>>> ''.join(reversed('1 2 3 4'))
'4 3 2 1'
n = 4
arr = map(int, "1 3 4 2".split())
ar = list(arr)
b=ar.reverse()
string =' '
string=string.join(str(ar))
print(string)
There are some mistakes in your code when you use map with int as a parameter the string is splitted to integers and the join function expects strings
One more thing the string.join function does not change the value of the string it just computes the value. If you want your strings value to be changed you should assign explicitly as in the code I have provided
You clearly need to join list of numbers. So unlike what others suggest, map(int, list) is correct.
sorting of list of strings that have number is not the same as sorting of list of strings.
That is, [121,17,11] will be [11,17,121] when you sort. But ["121","17","11"] will be ["11",121","17"]
>>> n = 4
>>> arr = map(int, "1 3 4 2".split())
>>> ar = list(arr)
>>> ar.reverse()
>>> string = ' '
>>> string.join(ar)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: sequence item 0: expected string, int found
>>> ar
[2, 4, 3, 1]
>>> map(str,ar)
['2', '4', '3', '1']
So you need to convert the list of int back to list of string and then join
>>> string.join(map(str,ar))
'2 4 3 1'
>>> print(string)
You are trying to join an int object, for your piece of code to work
you will have to replace your 3 line.
arr = map(str, "1 3 4 2".split())
Use the below method to join the elements:
string.join(str(x) for x in ar)
Looks like you solved the initial error of int vs str, nice work.
Now, string.join will return a new string, not modify the existing one in place.
So
n = 4
arr = map(str, "1 3 4 2".split())
ar = list(arr)
ar.reverse()
string = ' '
new_string = string.join(ar)
print(new_string)
returns
2 4 3 1
There are some cleaner ways to do what this is doing. For example
reversed_str = "".join(reversed("1 3 4 2"))
print(reversed_str)
in list, you can get a reversed list using list(reversed(array)).
and to convert list to string, you can do this:
some_str.join(str(x) for x in arr)
map(intpart and it should work.list(map()), eh. It also looks like you’re not saving the result of yourjoinanywhere.arr = map(int, "1 3 4 2".split())the "1 3 4 2" should be the input with that format. I simplified the code and tried to understand python. that's why i need the map() and turn it into a list.