Dictionaries

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For code examples see the [[Week2 Dictionaries Lab]]

Dictionaries are another collection variable but whose index is a set of keys, and are unordered. The keys also need not be integers but are usually characters. Dictionaries store "key-value" pairs, with values being accessed by their associated key.

Keys are the first elements. They must be

• immutable
• unique.

Each key is followed by a value separated by a colon. The values can be:

• immutable
• mutable
• duplicates.

Each key and value pair is separated by a comma.

char_dict = { "Name" : "Emily", "Species" : "Essai", "Designation": "Eclipse"}

Alternatively, this structure is also valid.

char_dict = { 
	"Name" : "Emily", 
	"Species" : "Essai", 
	"Designation": "Eclipse"
	}

Obtaining values from dictionaries

We use the keys to obtain the values from a dictionary.

E.g.

print(char_dict["Name"])
>>> Emily
print(char_dict["Designation"])
>>> Eclipse

Manipulating dictionaries

Add a key-value pair

We can add a key-value pair to an existing dictionary by using the assignment operator = when we call a key from the dictionary.

E.g.

char_dict["Father"] = "Morgan Medici"

char_dict = { 
	"Name" : "Emily", 
	"Species" : "Essai", 
	"Designation": "Eclipse",
	"Father" : "Morgan Medici"
}

Delete a key-value pair

We can delete a key-value pair from a dictionary by passing the dictionary while calling a specific key into the del() function.

E.g.

del(char_dict["Father"]) #oops, black hole got him

char_dict = { 
	"Name" : "Emily", 
	"Species" : "Essai", 
	"Designation": "Eclipse"
}

Checking if a key is in a dictionary

We can verify if a key is in a dictionary using the in command.

E.g.

sc_dict = dict( 
			Leviathan : "Claire McKinley",
			Behemoth: "Jon Smyth",
			Monarch : "Morgan Medici",
			Eclipse : "Emily Medici",
			Golem : "The Mother of the Essai"
			)
if "Monarch" in sc_dict:
	print("Monarch is active.")

Obtaining a list of keys and values

Keys

You can obtain a list of all keys in a dictionary using the keys() method.

E.g.

print(sc_dict.keys())
>>> ["Leviathan", "Behemoth", "Monarch", "Eclipse", "Golem"]

Values

Likewise, values can be obtained using the values() method.

print(sc_dict.values())
>>> ["Claire McKinley", "Jon Smyth", "Morgan Medici". "Emily Medici", "The Mother of the Essai"]