0loj.md

lang.py.data.dictionary

An associative array with mapped key: value pair

Synopsis

  my_dict = ["Daniel": 13, "Jose": 25]

Overview

A dictionary can contain any inmmutable value as it's keys. So you can use tuples as long as they do not conatin mutalbe objects either directly or indirectly

Keys must be unique within one dictionary. You can also use comprehension to create dictionaries

Cookbook

View a list of all the keys in a dictionary

You can use the list(), built-in function to return a list of all the keys defined in the dictionary in inserti order

  tel = {'jack': 4098, 'guido': 4139, 'irv': 3000}
  list(tel)         # ['jack', 'guido', 'irv']

• To view a sorted list of all the keys use sorted()

  tel = {'jack': 4098, 'guido': 4139, 'irv': 3000}
  sorted(tel)       # ['guido', 'irv', 'jack']

Change the value of a key

You can change the value pair of a given key by referencing it

  tel = {'jack': 4098, 'sape': 4139, 'guido': 4000}
  tel["guido"] = 4127
  print(tel)        # {'jack': 4098, 'sape': 4139, 'guido': 4127}

Delete a key value pair

You can delete a key and it's value with the del keyword

  tel = {'jack': 4098, 'sape': 4139}
  del tel["sape"]
  print(tel)        # {'jack': 4098}

Create a dictionary with iterable keys

Normally you wouldn't be able to pass an iterable as the key of a dictionary, other than strings, since they keys have to be inmutable and list an other iterables tend to be mutable

You can use frozensets to pass a set, an iterable, as the key of a dictionary

  key_1 = frozenset([1, 2])
  key_2 = frozenset([3, 4])

  my_dict = {key_1: 'good', key_2: 'bad'}
  pairs = []

  for key, value in my_dict.items():
      for element in key:
          pairs.append((element, value))

# [(1, 'good'), (2, 'good'), (3, 'bad'), (4, 'bad')]

Build dictionaries from sequences of key: value pairs

You can use the dict() built-in function to create dictionaries from key: value pairs

  tel = dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
  print(tel)        # {'sape': 4139, 'guido': 4127, 'jack': 4098}

Build a dictionary from two lists

Following the same process from the past recipe we can use the zip() function to build the list of key: value pairs from two separete lists

  names = ["Daniel", "Jose"]
  ages = [23, 22]
  my_dict = dict(zip(names, ages))
  print(my_dict)                    # {'Daniel': 23, 'Jose': 22}

Loop through key and values at the same time

When looping through dictionaries, the key and value can be retrieved at the same time using the items() method.

  knights = {'gallahad': 'the pure', 'robin': 'the brave'}
  for k, v in knights.items():
      print(k, v)

  # gallahad the pure
  # robin the brave

Loop over the keys of a dictionary

The default way of looping over a dictionary is doing it by it's keys

  for key in my_dict:
      print(key)

Get a list of the the values

You can get a list of all the values in your dictionary with the values() method

  for value in my_dict.values():
      print(value)