Creating a Dictionary

1. Literal syntax - {key: value,}

Key must be a hashable immutable type.

D = {
    'one': 'uno',
    2: 'dos',
    'three': 'tres',
    }

Output:

{'one': 'uno', 2: 'dos', 'three': 'tres'}

2. Use dict() value constructor and a pass keyword arguments

Key must be a string.

 D = dict(
     one = 'uno',
     two = 'dos',
     )

Output:
::

 {'one': 'uno', 'two': 'dos'}

3. Pass a collection (list) of a key-value pairs (tuples)

D = dict(
    [
        ('one', 'uno'),
        ('two', 'dos'),
        ('three', 'tres'),
    ]
)

Output:

{'one': 'uno', 'two': 'dos', 'three': 'tres'}

4. Use dict.fromkeys() method

Use collection as a dict keys [used before we had a “set” type]

Useful to count each letter in a word

from string import ascii_lowercase
D = dict.fromkeys(ascii_lowercase)
# D = dict.fromkeys(ascii_lowercase, 0)     # with default value

Output:

{'a': None,
 'b': None,
 'c': None,
 . . .
 'x': None,
 'y': None,
 'z': None}

5. Use a dict value constructor and pass it to an existing dictionary

Creates a shallow copy of the existing dict - keys are the same but values could be different.

D = {1:1, 2:4, 3:9}
D1 = dict(D)
D1[2], D2[3] = 8, 27
D, D1

Output:

({1: 1, 2: 4, 3: 9}, {1: 1, 2: 8, 3: 27})