<SYSTEM_TASK:>
Given the following text description, write Python code to implement the functionality described below step by step
<END_TASK>
<USER_TASK:>
Description:
 Dictionaries
We've been learning about sequences in Python but now we're going to switch gears and learn about mappings in Python. If you're familiar with other languages you can think of these Dictionaries as hash tables. 
This section will serve as a brief introduction to dictionaries and consist of
Step1:  Its important to note that dictionaries are very flexible in the data types they can hold. For example
Step2:  We can effect the values of a key as well. For instance
Step3:  A quick note, Python has a built-in method of doing a self subtraction or addition (or multiplication or division). We could have also used += or -= for the above statement. For example
Step4:  We can also create keys by assignment. For instance if we started off with an empty dictionary, we could continually add to it
Step5:  Nesting with Dictionaries
Hopefully your starting to see how powerful Python is with its flexibility of nesting objects and calling methods on them. Let's see a dictionary nested inside a dictionary
Step6:  Wow! Thats a quite the inception of dictionaries! Let's see how we can grab that value
Step7:  A few Dictionary Methods
There are a few methods we can call on a dictionary. Let's get a quick introduction to a few of them
<ASSISTANT_TASK:>
Python Code:
# Make a dictionary with {} and : to signify a key and a value
my_dict = {'key1':'value1','key2':'value2'}
# Call values by their key
my_dict['key2']
Explanation: Dictionaries
We've been learning about sequences in Python but now we're going to switch gears and learn about mappings in Python. If you're familiar with other languages you can think of these Dictionaries as hash tables. 
This section will serve as a brief introduction to dictionaries and consist of:
1.) Constructing a Dictionary
2.) Accessing objects from a dictionary
3.) Nesting Dictionaries
4.) Basic Dictionary Methods
So what are mappings? Mappings are a collection of objects that are stored by a key, unlike a sequence that stored objects by their relative position. This is an important distinction, since mappings won't retain order since they have objects defined by a key.
A Python dictionary consists of a key and then an associated value. That value can be almost any Python object.
Constructing a Dictionary
Let's see how we can construct dictionaries to get a better understanding of how they work!
End of explanation
my_dict = {'key1':123,'key2':[12,23,33],'key3':['item0','item1','item2']}
#Lets call items from the dictionary
my_dict['key3']
# Can call an index on that value
my_dict['key3'][0]
#Can then even call methods on that value
my_dict['key3'][0].upper()
Explanation: Its important to note that dictionaries are very flexible in the data types they can hold. For example:
End of explanation
my_dict['key1']
# Subtract 123 from the value
my_dict['key1'] = my_dict['key1'] - 123
#Check
my_dict['key1']
Explanation: We can effect the values of a key as well. For instance:
End of explanation
# Set the object equal to itself minus 123 
my_dict['key1'] -= 123
my_dict['key1']
Explanation: A quick note, Python has a built-in method of doing a self subtraction or addition (or multiplication or division). We could have also used += or -= for the above statement. For example:
End of explanation
# Create a new dictionary
d = {}
# Create a new key through assignment
d['animal'] = 'Dog'
# Can do this with any object
d['answer'] = 42
#Show
d
Explanation: We can also create keys by assignment. For instance if we started off with an empty dictionary, we could continually add to it:
End of explanation
# Dictionary nested inside a dictionary nested in side a dictionary
d = {'key1':{'nestkey':{'subnestkey':'value'}}}
Explanation: Nesting with Dictionaries
Hopefully your starting to see how powerful Python is with its flexibility of nesting objects and calling methods on them. Let's see a dictionary nested inside a dictionary:
End of explanation
# Keep calling the keys
d['key1']['nestkey']['subnestkey']
Explanation: Wow! Thats a quite the inception of dictionaries! Let's see how we can grab that value:
End of explanation
# Create a typical dictionary
d = {'key1':1,'key2':2,'key3':3}
# Method to return a list of all keys 
d.keys()
# Method to grab all values
d.values()
# Method to return tuples of all items  (we'll learn about tuples soon)
d.items()
Explanation: A few Dictionary Methods
There are a few methods we can call on a dictionary. Let's get a quick introduction to a few of them:
End of explanation
<END_TASK>