#!/usr/bin/env python3

# Dictionaries map a value to a key, hence a value can be

# called using the key.

# 1. They ar3333i3ie mutable, ie. they can be changed.

# 3. They are surrounded by curly {} brackets.

# 3. They are indexed using square [] brackets.

# 4. Key and Value pairs are separated by columns ":"

# 5. Each pair of key/value pairs are separated by commas ",".

# 6. Dicts return values not in any order.

# 7. collections.OrderedDict() gives an ordered dictionary.

# Create a dict

mydict1 = {}

# Add values to the dict.

mydict1["host1"] = "A.B.C.D"

mydict1["host2"] = "E.F.G.H"

print(mydict1)

# Remove values

del mydict1["host2"]

print(mydict1)

# Check if a key exists in a dict.

"host2" in mydict1

"host1" in mydict1

# Add elements to the dictionary

mydict1["host3"] = "I.J.K.L"

mydict1["host4"] = "M.N.O.P"

print(mydict1)

# Check the length of the dictionary

print(len(mydict1))

print(mydict1.keys())

released = {

"IPhone": 2007,

"IPhone 3G": 2008,

"IPhone 3GS": 2009,

"IPhone 4": 2010,

"IPhone 4S": 2011,

"IPhone 5": 2012,

"IPhone 5s": 2013,

"IPhone SE": 2016,

}

for i, j in released.items():

print("{0} was released in {1}".format(i, j))

# Change a value for a specific key

print("Changing the value for a key")

released["IPhone"] = 2006

released["IPhone"] += 1

print(released["IPhone"])

released["IPhone"] -= 1

print(released["IPhone"])