Kristian Rother at 19:58, 5 February 2013

2013-02-05T19:58:16Z

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{{Cat|Python Commands}}
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== 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.

<source lang="python">
prices = {
'banana':0.75,
'apple':0.55,
'orange':0.80
}
</source>

== 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.

<source lang="python">
print prices['banana']
print prices['kiwi']
</source>

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

<source lang="python">
for fruit in prices:
print fruit

# 0.75
# KeyError!
</source>

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

===== Checking whether a key exists: =====
<source lang="python">
prices.has_key('apple')
</source>

===== Retrieving values in a fail-safe way: =====
<source lang="python">
prices.get('banana') # 0.75

prices.get('kiwi')
</source>

===== Setting values if they dont exist yet: =====
<source lang="python">
prices.setdefault('kiwi',0.99)

prices.setdefault('banana',0.99)

# for 'banana', nothing happens.
</source>

===== Getting all keys / values: =====
<source lang="python">
print prices.keys()

print prices.values()

# None
</source>

Dictionaries - Revision history

Kristian Rother at 19:58, 5 February 2013