Python Fundamentals

Syntax: Below is how we can define a dictionary:

d = {

	key: value,
	key: value,
	.
	.
	key: value
}

• From Python 3.6 onwards, Dictionaries are ordered data structures, which means that they keep their elements in the same order in which they were introduced.
• Keys must be unique
• Key must of of a type that is immutable (a list of dictionary cannot be a key). Technically, key should be hashable, i.e. when passed to the built-in hash() method, should return the hash value. All immutable objects are hashable, but not all hashable objects are immutable.

We can also create a dictionary using the dict() function which takes a sequence (list of tuples below for example) of key-value pairs:

d = dict([(key,value),(key,value),...,(key,value)])

Below are some useful dictionary operations:

• dict_var[key]: Using the square bracket notation, we can access the associated value for the key.
• dic_var[key] = value: To add a new key-value pair. Can also be used to update the value for an existing key.
• del dict_var[key] will delete the specified key-value pair.
• key in dict_var to test of a key exists in the dictionary.
• len(dict_var) will return the number of key-value pairs.
• dict(zip(list1,list2)) will create a dictionary from. two lists. First list of items will be keys for the dictionary, and the second list of items will be the dictionary.
• key in dict_var check if the key exists.
• val in dict_var.values() check if the value exists