Author Dusty Phillips Reviewers

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The 
GOOG
stock was already in the dictionary, so when we tried to 
setdefault
it to 
an invalid value, it just returned the value already in the dictionary. 
BBRY
was not in 
the dictionary, so 
setdefault
returned the default value and set the new value in 
the dictionary for us. We then check that the new stock is, indeed, in the dictionary.
Three other very useful dictionary methods are 
keys()
, 
values()
, and 
items()
. The 
first two return an iterator over all the keys and all the values in the dictionary. We 
can use these like lists or in 
for
loops if we want to process all the keys or values. The 
items()
method is probably the most useful; it returns an iterator over tuples of 
(key, 
value)
pairs for every item in the dictionary. This works great with tuple unpacking 
in a 
for
loop to loop over associated keys and values. This example does just that to 
print each stock in the dictionary with its current value:
>>> for stock, values in stocks.items():
... print("{} last value is {}".format(stock, values[0]))
...
GOOG last value is 613.3
BBRY last value is 10.50
MSFT last value is 30.25
Each key/value tuple is unpacked into two variables named 
stock
and 
values
(we could use any variable names we wanted, but these both seem appropriate)
and then printed in a formatted string.
Notice that the stocks do not show up in the same order in which they were inserted. 
Dictionaries, due to the efficient algorithm (known as hashing) that is used to make 
key lookup so fast, are inherently unsorted.
So, there are numerous ways to retrieve data from a dictionary once it has been 
instantiated; we can use square brackets as index syntax, the 
get
method, the 
setdefault
method, or iterate over the 
items
method, among others.
Finally, as you likely already know, we can set a value in a dictionary using the
same indexing syntax we use to retrieve a value: