Exercise 8: Printing Printing

1. when to use %r instead of %s: e.g. %r shows with quotes when it is string

2. print str1 + str2,  #watch the comma at the end of it, is a space
    print str3 + str 4

3. code:

result:

4. """Double quotes, single quotes, triple double quotes and triple single quotes..."""
Watch the last print, why there are both double quotes and single quotes...