Dictionaries

Dictionaries are collections of key-value pairs. It supports mixed types of key-value pairs.

Example of a dictionary: fruitColors = {'apple': 'red', 'orange': 'orange', 'pear': 'green'}.

Useful Operations

Operator	Use	Explanation
[]	myDict[k]	Returns the value associated with k, otherwise its an error
in	key in adict	Returns True if key is in the dictionary, False otherwise
del	del adict[key]	Removes the entry from the dictionary

Additional Operations

Method Name	Use	Explanation
keys	adict.keys()	Returns the keys of the dictionary in a dict_keys object
values	adict.values()	Returns the values of the dictionary in a dict_values object
items	adict.items()	Returns the key-value pairs in a dict_items object
get	adict.get(k)	Returns the value associated with k, None otherwise
get	adict.get(k,alt)	Returns the value associated with k, alt otherwise

Time Complexity of Operations

operation	Big-O Efficiency
copy	O(n)
get item	O(1)
set item	O(1)
delete item	O(1)
contains (in)	O(1)
iteration	O(n)

Examples

Iterating a Dictionary

for key, value in dict.items():

print(key)

print(value)

Check if a Key Exists

if key in dictionary:

do_smth()

Sorting a Dictionary by Keys

d = {'apple':'red', 'orange':'orange'}

sorted(my_dict) # returns ['apple', 'orange']