[Tutor] A file containing a string of 1 billion random digits.

[Alan Gauld]

"Richard D. Moores" <rdmoores at gmail.com> wrote 

> Still, I understand yours, and not his (the return line). 

return "%0*d" % (n, random.randrange(10**n))

"%0*d"

The asterisk is quite unusual but basically means 
substitute the next argument but treat it as part of 
the format string. So:

>>> "%0*d" % (2,8)   # becomes same as "%02d"
'08'
>>> "%0*d" % (7,8)   # becomes same as "%07d"
'0000008'

So for the return statement with n = 4 it would give 

"%04d" % x

where x is a random number from range(10000).
That becomes

0dddd

where dddd is the random number


The same thing can be done in two steps with:

fmt = "%0%dd" % n   # eg. gives "%04d"  if n is 4
return fmt % randrange(....)

But the asterisk is neater (and faster) but can become hard to 
read, and debug, if over-used - like if there are many arguments 
in a single string!

HTH,

-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/