Dictionaries

Creating dictionaries

Dictionaries are an unordered, associative array. They have a set of key/value pairs. They are very versatile data structures, but slower than lists. Dictionaries can be used easily as a hashtable.

prices = {
'banana':0.75,
'apple':0.55,
'orange':0.80
}

Accessing elements in dictionaries

By applying square brackets with a key inside, the values of a dictionary can be requested. Valid types for keys are strings, integers, floats, and tuples.

print prices['banana']
print prices['kiwi']

Looping over a dictionary

You can access the keys of a dictionary in a for loop. However, their order is not guaranteed, then.

for fruit in prices:
print fruit

# 0.75
# KeyError!

Dictionary functions

There is a number of functions that can be used on every dictionary:

Checking whether a key exists:

prices.has_key('apple')

Retrieving values in a fail-safe way:

prices.get('banana') # 0.75

prices.get('kiwi')

Setting values if they dont exist yet:

prices.setdefault('kiwi',0.99)

prices.setdefault('banana',0.99)

# for 'banana', nothing happens.

Getting all keys / values:

print prices.keys()

print prices.values()

# None