Не могу исправить ошибку конкатенации Python

file = open("bin2.txt", 'w')
with open('bin2.txt', 'r'):
    for i in range(1000,9999):
        a = bin(i)[2:]
        file.write(str(a +'\n'))
file.close()

file0 = open("bin3.txt", 'w')
with open ("bin3.txt", 'r'):
    for i in range(1000,9999):
        newNum = ''
        while i > 0:
            newNum = str(i % 3) + newNum
            i //= 3
            file0.write(str(i+ '\n')) # **Здесь**
file0.close()