Make the substitution more explicit

[madchucky]

Different way of substituting the length of the string in format string as the %-formatting is called the "old %-formatting" in the documentation, be it for python:

• 2.7 https://docs.python.org/2.7/library/string.html?highlight=string#module-string or
• 3.6 https://docs.python.org/3.6/library/string.html?highlight=string#module-string