Introduction to Python

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Reading Multidimensional Containers: Looping

looping through a struct to read each "inner" structure

We begin by identifying the "inner" structures; 'for' looping takes us to each one in turn.

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

for inner_list in value_table:    # list, [ 1, 2, 3 ]

    print(inner_list[0])          # 1
                                  # 10
                                  # 100

• in this program we are looking to retrieve a value from each inner item of a multidimensional
• we first identify that each inner item is a list
• we can use a 'for' loop to assign each "inner" list to the control variable (here we have chosen to call it inner_list)
• next we can use subscripts to access a value within each "inner" list
• it is recommended to name your variables descriptively, for example inner_list -- this will keep the identity of each variable clear to you as you work

looping through and accessing values 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'  }
]

for inner_dict in lod:
    print(inner_dict['fname'])         # Ally
    print(inner_dict['lname'])         # Kane
    print()

                                       # Bernie
                                       # Bain

                                       # Josie
                                       # Smith

• we first identify this struct as a list of dicts
• looping through the "outer" list, we see that each item is a dict
• each "inner" dict has identical keys 'fname' and 'lname'
• as we loop through the list, each "inner" dict is assigned to the control variable (inner_dict); we can then access whatever values we wish by using simple dict subscripting on the "inner" dict

looping through and accessing values within a dict of dicts

In dict of dicts, looping through retrieves each key, and we must subscript to retrieve the "inner" dict.

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

for id_key in dod:
    inner_dict = dod[id_key]

    print((inner_dict['fname']))        # Ally
    print((inner_dict['lname']))        # Kane
    print()

• we first identify this struct as a dict of dicts
• looping through the "outer" dict, each key in the dict is assigned to the control variable (id_key)
• we then must use the key to get the value, which is the "inner_dict" for that key
• we can then subscript this "inner" dict for the values that we need

Ex. 7.16 -> 7.18 also to discuss building a struct from file (Ex. 7.25 -> 7.30)