Python 2nd Day

Data Type

• List
  • Compound data type, used to group together other values, which can be written as a list of comma-separated values (items) between square brackets.
  • All slice operations return a new list containing the requested elements. This means that the following slice returns a new (shallow) copy of the list:
    

  • >>> squares[:]
    [1, 4, 9, 16, 25]

  • lists are a mutable type.
  • looping a list:

  • >>> for i, v in enumerate(['tic', 'tac', 'toe']):
    ...     print(i, v)
    ...
    0 tic
    1 tac
    2 toe

  • looping over two or more sequences at the same time:

  • >>> questions = ['name', 'quest', 'favorite color']
    >>> answers = ['lancelot', 'the holy grail', 'blue']
    >>> for q, a in zip(questions, answers):
    ...     print('What is your {0}?  It is {1}.'.format(q, a))
    ...
    What is your name?  It is lancelot.
    What is your quest?  It is the holy grail.
    What is your favorite color?  It is blue.

• Dict
  • Unlike sequences, which are indexed by a range of numbers, dictionaries are indexed by keys, which can be any immutable type.
  • It is best to think of a dictionary as an unordered set of key:value pairs, with the requirement that the keys are unique.
  • Performing list(d.keys()) on a dictionary returns a list of all the keys used in the dictionary, in arbitrary order (if you want it sorted, just use sorted(d.keys()) instead).
  • looping a dict:

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