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10/28/09

Dictionaries

Emad Nawfal

10/28/09

A minimal dictionary

english2arabic = {'man': 'rajul',

'country': 'balad',

'peace': 'salam',

'terror': 'irhab',

'child': 'tifl'}

10/28/09

Dictionaries have pairs of items.Each item has a key and a value.Dictionaries are indexed by keys, not

by digits indicating position as in lists

The key has to be an immutable type: what are immutable types?

The values can be anything.

10/28/09

Dictionaries support the in operator (tests for keys, not values)

Dictionaries support iterationThe .values() method gets us all the

values.The .keys() method gets us all the

keys.The .items() method gets us all the

items.Dict1.py as an example

10/28/09

Building dictionaries programmatically

It is very tedious to build dictionaries by hand.

You can build dictionaries programmatically easily in two steps:

Initialize a dictionary

Update the dictionary keys.

10/28/09

Counting words with dictionaries

Question: How do you count word frequencies in a text?

Can we use: listname.count(x)? Dictionaries: buildDict.py Default dictionaries: countWords.py

10/28/09

Advanced Topics

Dictionaries of dictionaries Dictionaries of lists Lists of dictionaries Use a database if possible. Things get

ugly quickly.