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``````# CS 8

# Midterm 2:
#   - Mean
#   - std:

''' A few notes about Lab07
- Lab07 uses tuples as a way to organize certain data.
- One of the requirements is to print certain data in
descending order
- We talked about sorting lists
'''

L = ["b","c","a"]
L.sort()
print(L)

# but what if we had a list of tuples? How would the list sort
# these items?

L = [(1,3),(3,2),(3,1),(3,3),(0,1)]
L.sort()
print(L)

# by default, list.sort() will sort the first value and then by
# the 2nd value in the case of a tie.
# We can reverse the sorting order (descending instead of ascending)

L.sort(reverse=True)
print(L)

''' Dictionaries
- New Tool: DICTIONARIES
- Otherwise known as TABLES or MAPS
- Works where a KEY maps to a VALUE
- Use dictionaries for two main reasons:
- Gives us more precise indexing than Lists
- L['someString'] - allows us to index elements
based on some key
- Performance is MUCH better than searching through
Lists.
- keys are HASHED to a specific index value
- keys are passed through some math equation
and an index is computed
- Provides DIRECT ACCESS to the value given a
key.
- Details of hashing is not discussed in this class,
but you may see it sometime...
'''
''' Syntax for Dictionaries
{<key1>:<value1>,<key2>:<value2>, ... , <keyn>:valuen>}
'''

D = {} # Empty dictionary. Notice the curly braces instead of []

D = {'Jane':18, 'Jen':19, 'Joe':20, 'John':21}

'''
print(D)
print("Jane's age is:", D['Jane'])
print(len(D))

# Simple way to get key / value
for x in D:
print(x) # Prints the keys
print(D[x]) # Prints the values
'''
''' Restrictions on using Dictionaries
- Keys must be an immutable type (int, str, namedtuples, - not
lists for example).
- Values can be anything (mutable or immutable objects)
- For our purposes, KEYS are UNIQUE. Don't define something like
{'Joe':17, 'Joe':18}.
- Python is actually OK with duplicate keys and it will return
the last key/value in the dictionary.
- Again, for our purposes, we should never use duplicate key
values (kinda defeats the purpose of dictionaries).
'''

''' dictionary methods
D.pop(key) # remove and return the value
D.update(D2) # combine values in D and D2
D.get(key) # returns item if it exists. If not, returns None or a default value
D.keys() # dict_keys([ LIST OF KEYS ])
D.values() # dict_values([ LIST OF VALUES ])
D.items() # dict_items([ LIST OF KEY,VALUE ])
'''
'''
value = D.pop('John')
print(D)
print(value)
D.update({'Jess':25,'Jerry':27})
print(D)

# What if something is not in the dictionary and we try to access it?
#print(D["CS8"]) #ERROR - "CS8" key doesn't exist.
print(D.get("CS8"))

# Can define the default return value if key doesn't exist
print(D.get("CS8", "not in dictionary!"))

print(D.keys())
print(D.values())
'''
'''
for item in D.keys():
print(item)
'''
'''
keys = D.keys()
#print(keys) # ERROR - Not a list!
print(list(keys)) # OK
'''

# Example of adding to a dictionary
D = {}
print(D)
D['CS8'] = "UCSB"
print(D)
D['CS16'] = "UCSB"
print(D)
'''

``````