CHAP 9 COSC 1010

dictionary

object that stores a collection of data, consists of a key and value

retrieve value

dictionary_name[key]

add elements

dictionary[key]=value

delete elements

del dictionary[key]

len function

empty dictionary

use {}

for loop

for key in dictionary:, for item in set:

clear method

deletes all the elements in a dictionary, leaving it empty (dictionary.clear())

get method

gets a value associated with specified key from the dictionary (dictionary.get(key, default))

items method

returns all the dictionaries keys and associated values (dictionary.items())

keys method

returns all the dictionaries keys as a sequence (dictionary.keys())

pop method

returns value associated with specified key and removes that key-value pair from the dictionary (dictionary.pop(key, default))

popitem method

Returns, as a tuple, the key-value pair that was last added to the dictionary, also removes the key-value pair from dictionary (dictionary.popitem())

values method

returns all the dictionaries values as a sequence (dictionary.values())

dictionary comprehension

an expression that reads a sequence of input elements and uses those input
elements to produce a dictionary (squares={item**2 for item in numbers})

set

object that stores a collection of data in same way as mathematical set (mutable)

set function

used to create a set, empty set call set(), non-empty call set(argument)

len function

returns the number of elements in the set

add method

adds an element to a set

update method

adds a group of elements to a set, elements must be iterable

remove + discard methods

remove the specified item from the set, remove raises KeyError, discard does not

clear method

clears all the elements of the set

in operator

used to test whether a value exists in set, not in as well

union of two sets

a set that contains all the elements of both sets (set3=set1.union(set2) or set1 | set2)

intersection of two sets

a set that contains only the elements found in both sets (set3=set1.intersection(set2) or set1 & set2)

difference of two sets

a set that contains elements that appear in the first set but do not appear
in second set (set3=set1.difference(set2) or set1-set2)

symmetric difference of two sets

a set that contains the elements that are not shared by the two sets (set1.symmetric_difference(set2) or set1^set2)

subset

Set A is subset of set B if all the elements in set A are included in set B (setA.issubset(setB) or setA <= setB)

superset

Set A is superset of set B if it contains all the elements of set B (setA.issuperset(setB) or setA >= setB)

set comprehension

a concise expression that creates a new set by iterating over the elements of a
sequence (set2={item for item in set1})

serialize an object

convert the object to a stream of bytes that can easily be stored in a file

pickling

serializing an object, import pickle (pickle.dump(object, file)) then close

unpickling

retrieving pickled object, import pickle then open file (pickle.load(file)) then close