Write a method named addCommas that accepts a string representing a number and returns a new string with a comma at every third position, starting from the right. For example, the call of addCommas("12345678") returns "12,345,678".

Locale unaware

'{:,}'.format(value) # For Python ≥2.7

f'{value:,}' # For Python ≥3.6

Locale aware

import locale

locale.setlocale(locale.LC_ALL, '') # Use '' for auto, or force e.g. to 'en_US.UTF-8'

'{:n}'.format(value) # For Python ≥2.7

f'{value:n}' # For Python ≥3.6

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