Introduction to Python

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Reading Multidimensional Containers: Subscripting

pinpointing a specific value within a structure

We can use subscripts to "travel to" a value within a multidimensional.

value_table =       [
                       [ 1, 2, 3 ],
                       [ 10, 20, 30 ],
                       [ 100, 200, 300 ]
                    ]

val1 = value_table[0][0]       # float, 1
val2 = value_table[0][2]       # float, 3
val3 = value_table[2][2]       # float, 300

• If we are intending to retrieve a single value from a multidimensional, we can use subscripts to pinpoint the target value.
• This "outer" list has 3 items -- each item is a list, and each list represents a row of data. Each "inner" list has 3 items.
• In this case, the calculation is simple - count indices to the "row" you want, then count indices to the item.
• (Remember that indexing begins at 0.)

pinpointing a value within a list of dicts

In a list of dicts, each item is a dict.

lod = [
    { 'fname': 'Ally',
      'lname': 'Kane'   },
    { 'fname': 'Bernie',
      'lname': 'Bain'   },
    { 'fname': 'Josie',
      'lname': 'Smith'  }
]

val = lod[2]['lname']         # 'Smith'

val2 = lod[0]['fname']        # 'Ally'

• The "outer" list contains 3 items, each item a dictionary
• Each "inner" dictionary has identical keys 'fname' and 'lname'
• Our first subscript will be a list index that locates the dict we need, and the 2nd will be a dict key to get the value within that dict.

pinpointing a value in a dict of dicts

A dict of dicts has string keys and dict values.

dod = {
    'ak23':  { 'fname': 'Ally',
               'lname': 'Kane' },
    'bb98':  { 'fname': 'Bernie',
               'lname': 'Bain' },
    'js7':   { 'fname': 'Josie',
               'lname': 'Smith' },
}

val = dod['ak23']['fname']     # 'Ally'

val2 = dod['js7']['lname']     # 'Smith'

• The "outer" dict has 3 keys, each associated with a dictionary.
• Each "inner" dictionary has identical keys 'fname' and 'lname'.
• So our first subscript will be a dict key that locates the "inner" dict we need, and the 2nd will be another dict key to get the value within that dict.

Ex. 7.8 -> 7.10