Overview

Hour 1
- Tuples
- Dictionaries
- Take Up Midterm
Hours 2 and 3
- Work Time

Lists

A list is an object that contains multiple data items
Lists are mutable
Lists can be indexed and sliced
Lists have methods

Syntax

Square brackets
Commas as separators



In [33]:

    
number_list = [1, 2, 4, 8, 16, 32]
the_pythons = ["Graham", "Terry",  "Michael", "Eric", "Terry", "John"]
mixed = [1, "Terry", 4]

print (mixed)









    



[1, 'Terry', 4]

Tuple

A tuple is an immutable version of a list
Immutable means that the contents cannot change after creation

Syntax

Parentheses
Commas as separators



In [34]:

    
monty = ("Graham", "Terry",  "Michael", "Eric", "Terry", "John")



In [35]:

    
# the entire tuple
print (monty)









    



('Graham', 'Terry', 'Michael', 'Eric', 'Terry', 'John')



In [36]:

    
# one element at a time
for name in monty:
    print(name)









    



Graham
Terry
Michael
Eric
Terry
John



In [39]:

    
# indexing
print(the_pythons[2])

print(monty[2])









    



Michael
Michael

[] brackets or square brackets () parentheses {} curly braces or braces

Converting Between Lists and Tuples

list()
tuple()



In [7]:

    
# monty is the tuple, and the_pythons is a list
print (monty)
print (list(monty))









    



('Graham', 'Terry', 'Michael', 'Eric', 'Terry', 'John')
['Graham', 'Terry', 'Michael', 'Eric', 'Terry', 'John']



In [9]:

    
print (the_pythons)
print (tuple(the_pythons))









    



['Graham', 'Terry', 'Michael', 'Eric', 'Terry', 'John']
('Graham', 'Terry', 'Michael', 'Eric', 'Terry', 'John')

Why?

Performance
- Tuples are faster
Safety
- Can't be modified

Looking ahead: tuples can be keys in a dictionary, but lists can't



In [ ]:

    
# Safer than constants, because it is enforced by interpreter
CONVERSION_CONSTANT = 5/9

Dictionaries

A dictionary is a collection data structure. Each element in a dictionary has two parts: a key and a value. You use a key to locate a specific value.
Shorthand description: a dictionary is like a list, but instead of the index being a number, the index is any value, e.g. int, float, string, tuple, etc.
Think dictionaries and phone books



In [20]:

    
my_dict = {}
my_dict[3.14] = "pi"
my_dict["pi"] = 3.14159
my_dict[(1,2)] = "x,y coordinates"
my_dict[(2,3)] = "x,y coordinates"
print my_dict









    



{(1, 2): 'x,y coordinates', 'pi': 3.14159, (2, 3): 'x,y coordinates', 3.14: 'pi'}



In [40]:

    
my_dict[(1,2)] = [4, 5, 6, 7]
print my_dict









    



{(1, 2): [4, 5, 6, 7], 'pi': 3.14159, (2, 3): 'x,y coordinates', 3.14: 'pi'}



In [41]:

    
len(my_dict)









    Out[41]:





4



In [14]:

    
phone_book = {"Graham":"555-111", 
              "Terry": "555-2222", 
              "Michael": "555-3333"}

Retrieving a Value from a Dictionary

dictionary[key]



In [15]:

    
phone_book









    Out[15]:





{'Graham': '555-111', 'Michael': '555-3333', 'Terry': '555-2222'}



In [18]:

    
phone_book['Michael']









    Out[18]:





'555-3333'



In [42]:

    
my_dict[(1,2)]









    Out[42]:





[4, 5, 6, 7]



In [43]:

    
phone_book['Wanda']









    



---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-43-7a063856545e> in <module>()
----> 1 phone_book['Wanda']

KeyError: 'Wanda'

Testing for Value in a Dictionary



In [45]:

    
# Using 'in'

if "Michael" in phone_book:
    print phone_book["Michael"]



In [46]:

    
# Using 'not in'

if "Wanda" not in phone_book:
    print("Fish don't need phone numbers")









    



Fish don't need phone numbers

Adding Elements to a Dictionary



In [49]:

    
print(phone_book)

# Eric, Terry, John

phone_book["Eric"] = "555-4444"
phone_book["Terry"] = "555-5555"
phone_book["John"] = "555-6666"









    



{'Michael': '555-3333', 'John': '555-6666', 'Graham': '555-111', 'Eric': '555-4444', 'Terry': '555-5555'}

Deleting Elements

del dictionary[key]



In [50]:

    
del phone_book["John"]



In [51]:

    
print(phone_book)









    



{'Michael': '555-3333', 'Graham': '555-111', 'Eric': '555-4444', 'Terry': '555-5555'}

Putting it together

Test for presence of key before deletion



In [53]:

    
if 'Michael' in phone_book:
    del phone_book['Michael']

print(phone_book)









    



{'Graham': '555-111', 'Eric': '555-4444', 'Terry': '555-5555'}



In [54]:

    
if '555-4444' in phone_book:
    print ("Can match values too!")

Iterating over a Dictionary



In [55]:

    
for name in phone_book:
    print (name, phone_book[name])









    



('Graham', '555-111')
('Eric', '555-4444')
('Terry', '555-5555')

Dictionary Methods



In [56]:

    
phone_book.items()









    Out[56]:





[('Graham', '555-111'), ('Eric', '555-4444'), ('Terry', '555-5555')]



In [57]:

    
phone_book.keys()









    Out[57]:





['Graham', 'Eric', 'Terry']



In [58]:

    
phone_book.values()









    Out[58]:





['555-111', '555-4444', '555-5555']



In [59]:

    
if '555-4444' in phone_book.values():
    print("We can match values too")









    



We can match values too

Midterm Discussion



In [62]:

    
even = False
if even = True: 
    print("It is even!")









    



  File "<ipython-input-62-f4a5eccef0b1>", line 2
    if even = True:
            ^
SyntaxError: invalid syntax



In [63]:

    
154 >= 300 != False









    Out[63]:





False



In [71]:

    
def is_equal(t1, t2):
#    return t1 == t2
    return t1.sort() == t2.sort()

list1 = ["name", "age", "temp"]
list2 = ["name", "temp", "age"]

if is_equal(list1, list2):
    print("Same!")
else:
    print ("Different!")









    



Same!