Python regex: Finding input not matching a specific (variable-defined) length -

i'm writing regular expressions in python, keep getting problem:

typeerror: 'int' object not iterable.  

my regular expression:

searchresults = (re.findall("[0-9]{"+re.escape(columns)"}",content)) 

my variable columns length of first element of set (len(..)) of regular expression. when i'm using normal number works. when try print(columns), see normal number.

thanks help!

sample of content:

111111111111 100111011101 180101020111 1001010000112 101610170051 150100111001 101100111101 100010000111 100000801111 100081010111 111111111111 

sample columns: 12

as result i'm trying line (which not have 12 numbers): 1001010000112

if want filter strings of not matching specific length, following trick:

re.findall('(^[0-9]{0,%d}$|[0-9]{%d}[0-9])' % (columns, columns), s)