Dictionaries are used to store data values in key:value pairs. A dictionary is a collection which is ordered (from Python 3.7 onwards), changeable, and does not allow duplicate keys.

1. Create dictionary

Dictionaries are written with curly brackets {}, and have keys and values.

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict)

Dictionary items are presented in key:value pairs, and can be referred to by using the key name. Duplicate keys are not allowed; if you specify the same key twice, the second value will overwrite the first.

2. Access items

You can access the items of a dictionary by referring to its key name, inside square brackets.

x = thisdict["model"] # "Mustang"

You can also use the get() method to achieve the same result. get() is safer because it returns None instead of throwing an error if the key does not exist.

x = thisdict.get("model")

Getting Keys, Values, and Items

keys(): Returns a list of all the keys.
values(): Returns a list of all the values.
items(): Returns a list of tuples containing each key-value pair.

keys = thisdict.keys()
values = thisdict.values()
items = thisdict.items()

3. Change values

You can change the value of a specific item by referring to its key name.

thisdict["year"] = 2018

You can also use the update() method to update the dictionary with items from a given argument (a dictionary or an iterable of key-value pairs).

thisdict.update({"year": 2020})

4. Add items

Adding an item to the dictionary is done by using a new index key and assigning a value to it.

thisdict["color"] = "red"

You can also use the update() method here; if the key does not exist, it will be added.

5. Remove items

There are several methods to remove items from a dictionary:

pop(): Removes the item with the specified key name.
```
thisdict.pop("model")
```
popitem(): Removes the last inserted item.
```
thisdict.popitem()
```
del: Removes the item with the specified key name. It can also delete the dictionary completely.
```
del thisdict["year"]
```
clear(): Empties the dictionary.
```
thisdict.clear()
```

6. Loop through dictionary

You can loop through a dictionary by using a for loop. When looping, the return value are the keys, but there are methods to return the values as well.

# Loop through keys
for x in thisdict:
    print(x) # prints keys

# Loop through values
for x in thisdict.values():
    print(x)

# Loop through both keys and values
for x, y in thisdict.items():
    print(x, y)

7. Nested dictionaries

A dictionary can contain dictionaries, this is called nested dictionaries.

myfamily = {
  "child1" : {
    "name" : "Emil",
    "year" : 2004
  },
  "child2" : {
    "name" : "Tobias",
    "year" : 2007
  }
}

print(myfamily["child2"]["name"]) # Tobias

8. Dictionary methods

Python has a set of built-in methods that you can use on dictionaries.

Method	Description
`clear()`	Removes all the elements from the dictionary
`copy()`	Returns a copy of the dictionary
`fromkeys()`	Returns a dictionary with the specified keys and value
`get()`	Returns the value of the specified key
`items()`	Returns a list containing a tuple for each key value pair
`keys()`	Returns a list containing the dictionary’s keys
`setdefault()`	Returns the value of the specified key. If the key does not exist: insert the key, with the specified value