Positive/Negative Indexes, Slicing

  • Lists, strings, and tuples have a positive index system:
["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]   
0      1      2      3      4      5      6
  • And a negative index system:
["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]  
-7     -6     -5     -4     -3     -2     -1
  • In a list, the 2nd, 3rd, and 4th items can be accessed with:
days = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
days[1:4]
Output: ['Tue', 'Wed', 'Thu']
  • First three items of a list:
days = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
days[:3]
Output:['Mon', 'Tue', 'Wed'] 
  • Last three items of a list:
days = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
days[-3:]
Output: ['Fri', 'Sat', 'Sun']
  • Everything but the last:
days = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
days[:-1] 
Output: ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'] 
  • Everything but the last two:
days = ["Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"]
days[:-2] 
Output: ['Mon', 'Tue', 'Wed', 'Thu', 'Fri'] 
  • A single in a dictionary can be accessed using its key:
phone_numbers = {"John Smith":"+37682929928","Marry Simpons":"+423998200919"}
phone_numbers["Marry Simpsons"]
Output: '+423998200919'