What about
>>> a = range(100)
>>> a[78:80] + a[85:97]
[78, 79, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96]
Update: Not sure what you want as the output for your string example:
>>> import string
>>> a = list(string.lowercase[:7])
>>> a[1:3] + a[4:6]
['b', 'c', 'e', 'f']