[Tutor] Adding line numbers to a Python Script

[Sudip Bhattacharya]

I quote this example (and the problem that I am facing trying to understand)
from the book "Beginning Python - From Novice to Professional" by Magnus Lie
Hetland

Page 227

# numberlines.py
import fileinput........................(1)

for line in fileinput.input(inplace = true)............(2)
   line = line.rstrip()........................................(3)
   num=fileinput.lineno()..................................(4)
   print '%-40s #%2i' %(line,num).....................(5)


Question: Please help me understand:

Line (3) - Are we stripping the entire line of code first, inserting the
code at the end (line (5)) and then placing it back at the same place ?

Line (5) - What does the individual characters in the expression "Print
'%-40s #%2i' %(line,num)" mean ?

     - '-40s' : is this the space [what does "-40s" mean] that we are
creating post - which the line nos is inserted "#%2i" ?
     - What does '%2" mean ? - Is that 2 cursor spaces of width ?

Much thanks in advance...
-- 
Thanks and regards,
Sudip Bhattacharya

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