Writing data to multiple folders in Python

I am trying to write A in multiple folders, namely, 1,2,3,4,5 with file name A.txt. But I am getting an error. How do I fix it?

import os

Runs=5

def function(run):
    from scipy.stats import truncnorm
    import numpy as np
    import csv 
    
    parent_folder = str(run + 1)
    os.mkdir(parent_folder)

    A=3


    ######################################

    with open(os.path.join(parent_folder, rf"A.txt"), 'w+') as f: 
        
        #print("A =",[A])
        writer = csv.writer(f)
        writer.writerow(A)
     


for x in range(Runs):
    function(x)

The error is

in function
    writer.writerow(A)

Error: iterable expected, not int

>Solution :

There appears to be a dearth of answers explaining what the actual problem is among the possible duplicates on this site, so here goes.

csv.csvwriter.writerow expects an iterable of elements that represents a row of data. It can’t and won’t guess that a single element should be treated specially (what the error is telling you). If you try to pass in something that’s only accidentally an iterable, such as a string, each character will be treated as a separate element. To correctly write a row, wrap it in an iterable, such as a list, tuple, or even generator:

[A]
(A,)
(A for _ in range(1))