Python Introduction | Lists, Tuples, Ranges, Sets, and Dictionaries | Managing Values with Dictionaries

Lists and tuples manage values by numeric index. Python dictionaries manage values by key instead.

Create a dictionary with braces or with dict.

variable = {key1: value1, key2: value2, ...}
variable = dict(key1=value1, key2=value2, ...)

Use brackets to retrieve or assign a value.

variable = dictionary[key]
dictionary[key] = value

A dictionary uses keys, not numeric positions. It is not a sequence.

Using for in

Iterating over a dictionary returns its keys. Use each key to retrieve its value.

dic = {'taro':'taro@yamada.com',
       'hanako':'hanako@flower',
       'ichiro':'ichiro@baseball'}
for n in dic:
    print(n + ' (' + dic[n] + ')')

This example uses names as keys and email addresses as values. Dictionaries are useful for small database-like collections.

dictionary[key] = value

If the key does not exist, Python adds a new entry. If it exists, Python updates the value.

del dictionary[key]

variable = dictionary.keys()

variable = dictionary.values()

variable = dictionary.items()

items() returns key-value pairs. Choose dictionaries when named keys are more useful than numeric positions.