Classwork:

Two ways to create a dictionary in python:
1.

grocery1 = {'lettuce': 1.99, 'tomato': 0.49, 'onion': 0.35, 'olives': 0.99}

2.

grocery2 = {}
grocery2['lettuce'] = 1.99
grocery2['tomato'] = 0.49
grocery2['onion'] = 0.35
grocery2['olives'] = 0.99
grocery2
{'olives': 0.99, 'tomato': 0.49, 'onion': 0.35, 'lettuce': 1.99}

Two ways to insert a new key-value pair to the dictionary:
1.

grocery1['lemon'] = 0.78
grocery1
{'olives': 0.99, 'lemon': 0.78, 'tomato': 0.49, 'onion': 0.35, 'lettuce': 1.99}

2.

grocery1.update({'potato':1.10})
grocery1
{'lemon': 0.78, 'onion': 0.35, 'potato': 1.1, 'olives': 0.99, 'tomato': 0.49, 'lettuce': 1.99}

Two ways to create a list of the keys of the dictionary:
1.

keys = grocery1.keys()
keys
dict_keys(['lemon', 'onion', 'potato', 'olives', 'tomato', 'lettuce'])
for key in keys:
print(grocery1[key], end = '-')
0.78-0.35-1.1-0.99-0.49-1.99-

print(keys)
dict_keys(['onion', 'tomato', 'olives', 'lettuce'])
for key in keys:
print(key, end = ' ')
onion tomato olives lettuce

2.

keys_list = list(grocery1.keys())
keys_list
['lemon', 'onion', 'potato', 'olives', 'tomato', 'lettuce']
 

Two ways to create a list of values:
1.

values_list = []
for key in keys:
    values_list += [grocery1[key]]

values_list
[0.78, 0.35, 1.1, 0.99, 0.49, 1.99]
 

2.

val_list = grocery1.values()
val_list
dict_values([0.78, 0.35, 1.1, 0.99, 0.49, 1.99])
 

More to know:

x = 'lemon' in grocery
x
True

y = 'carrot' in grocery
y
False

How to delete a key-value entry pair from a dictionary:

grocery1 = {'lettuce': 1.99, 'tomato': 0.49, 'onion': 0.35, 'olives': 0.99}
del grocery1['lettuce']
grocery1
{'onion': 0.35, 'tomato': 0.49, 'olives': 0.99}

In edmodo.com
Homework:
Answer the following questions in edmodo.com

1. Do lists allow duplicate elements? what about dictionaries?

adict = {'a':1,'b':2,'a':4}
adict
{'a': 4, 'b': 2}

2. What are two ways to insert key–> value pairs into a dictionary.
3. Can different ‘types’ of keys be used in the same dictionary?
4. What happens when you try entering a value for a key that is already in the dictionary?
5. Create a scenario in which you would use a dictionary (without using the grocery example from these slides), and explain why you’d use a dictionary rather than a list.

Gota, you were right. Here is another way to add a key-value pair to a dictionary from stackoverflow.com

x = {1:2}
print x
{1: 2}

x.update({3:4})
print x
{1: 2, 3: 4}