def pad(s, destination_size=None):
"""Pad a string using different whitespace characters to stop Twitter
from thinking two tweets are the same.
Will try to add 10% whitespace to the string.
"""
if not destination_size:
destination_size = min(len(s) + max(int(len(s)*0.1), 5), 140)
padding = ''
for i in range(len(s), destination_size):
padding += Alphabet.random_whitespace()
return s + padding
