[Tutor] Cosmetic question about printing

[Steve Willoughby]

On Tue, May 6, 2008 11:35, Dick Moores wrote:

> Could someone just come right out and do it for me? I'm lost here.
> That '*' is just too magical..  Where did you guys learn about
> '%*s'? Does the '%s' still mean a string?

Python's % operator (for string formatting) is derived from the C standard
library function printf(), which also accepts the %*s notation.  It's
capable of a lot of powerful features you may not be aware of.  See
printf(3) for full details (you can google for printf if you don't have
manpages on your system).

In a nutshell, between the % and the s you can put the desired field
width, like "%10s" which means to pad out the data in the string to be at
least 10 characters, right-justifying the column.  "%-10s" means to left
justify it.  If the string being printed is longer than that, it's just
printed as-is, it's not truncated.  But you can specify that if you like,
too: "%10.10s"

In place of either of those numbers, you can use "*" which just means
"pick up the desired width from the next value in the tuple", which allows
you to compute the width on the fly, which is what's being done here.

Try this:

def print_result(date1, date2, days1, weeks, days2):
  line1 = 'The difference between %s and %s is %d day%s' % (
    date1.strftime('%m/%d/%Y'),
    date2.strftime('%m/%d/%Y'),
    days1, ('' if days1 == 1 else 's'))
  line2 = 'Or %d week%s and %d day%s' % (
    weeks, ('' if weeks == 1 else 's'),
    days2, ('' if days2 == 1 else 's'))

  print line1
  print '%*s' % (len(line1), line2)