University of Arizona, Department of Computer Science

CSc 120: Update a 2-level dictionary

Definitions

A two-level dictionary is analogous to a list-of-lists (aka "2D-list"), except that it involves dictionaries rather than lists:

A list-of-lists L is a list where each element L[someidx] is itself a list; and L[someidx][anotheridx] gives us a value stored in L.
Analogously, a two-level dictionary D is a dictionary-of-dictionaries: D[somekey] is itself a dictionary, and D[somekey][anotherkey] gives us a value stored in the two-level dictionary D. In this example, somekey is called the first-level key and anotherkey is called the second-level key.

In the examples below, DD is assumed to be the following two-level dictionary:

{ 'aaa' : { 'bbb' : 'string1', 'ccc' : 'string2', 'ddd' : 'string3' },
  'bbb' : { 'ccc' : 'string4', 'ddd' : 'string5', 'eee' : 'string6', 'fff' : 'string7' },
  'ccc' : { 'aaa' : 'string8', 'bbb' : 'string9' }
}

Thus, we have: DD['bbb']['ccc'] is the value 'string4', while DD['ccc']['bbb'] is 'string9'.

Expected Behavior

Write a function update_dict2(dict2, key1, key2, value), where dict2 is a two-level dictionary; key1 is the first-level key; key2 is the second-level key; and value is a value to be stored at dict2[key1][key2]. This function should return a dictionary obtained by updating dict2 such that in the resulting dictionary, which we refer to as newdict2, the following holds:

newdict2[key1][key2] == value.

Examples

DD is the two-level dictionary shown above (under Definitions).

update_dict2(DD,'aaa','ccc',12)
return value:

{ 'aaa' : { 'bbb' : 'string1', 'ccc' : 12, 'ddd' : 'string3' },
  'bbb' : { 'ccc' : 'string4', 'ddd' : 'string5', 'eee' : 'string6', 'fff' : 'string7' },
  'ccc' : { 'aaa' : 'string8', 'bbb' : 'string9' }
}

update_dict2(DD,'aaa','ggg','string17')
return value:

{ 'aaa' : { 'bbb' : 'string1', 'ccc' : 12, 'ddd' : 'string3', 'ggg' : 'string17' },
  'bbb' : { 'ccc' : 'string4', 'ddd' : 'string5', 'eee' : 'string6', 'fff' : 'string7' },
  'ccc' : { 'aaa' : 'string8', 'bbb' : 'string9' }
}

update_dict2(DD,'ggg','aaa','string17')
return value:

{ 'aaa' : { 'bbb' : 'string1', 'ccc' : 12, 'ddd' : 'string3' },
  'bbb' : { 'ccc' : 'string4', 'ddd' : 'string5', 'eee' : 'string6', 'fff' : 'string7' },
  'ccc' : { 'aaa' : 'string8', 'bbb' : 'string9' },
  'ggg' : { 'aaa' : 'string17' }
}