Class 21 — Wednesday, October 13

Look at the map

I say love is love — For aren’t we all just people — Living as we are

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Look both ways

• Back or ahead

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Agenda

• Introduce dict

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To do

• Examine artifacts

• Examine dict module documentation

• Examine collections epistle

• Examine while epistle

• Homework

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Examples

• Program romantic.py

• Program unromantic.py

• Program floradation.py

• Program even_odd.py

• Program good_doggie.py

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Some data sets

• romans.csv

• babelfish

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Problem romantic.py

• Get a roman numeral and determine its integer equivalent

Some program runs

Enter Roman numeral: V

5

Enter Roman numeral: d

500

Enter Roman numeral: 0

Unknown

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Problem unromantic.py

• Get a word and print its English equivalent

Some program runs

RecursionError: maximum recursion depth exceeded during compilation

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Discussion

• Repeat the word carrot ten times out loud

• The human brain is great with associations; e.g., many of us associate apple with red, sky with blue, and programming with fun.

• A dict is Python's software equivalent of a collection of associations. In particular, a dict is an un-ordered collection of associations.

• The elements of a dict are called mappings. A mapping associates one object (called the key) with another object (called the value).

• The literal for an empty dict is {}.

• A literal mapping is written using the : to separate the key with its value. For example, the below variable flora_to_color is a dict that associates flora with colors.

flora_to_color = { 'spruce': 'green', 'apple': 'red', 'shamrock': 'green',

  'banana': 'yellow', 'potato': 'brown', 'eggplant': 'purple' }

• The len() function works on a dict. For example, len( flora_to_color ) is 6, because the definition of flora_to_color specified six mappings.

• The brackets [] operator in conjunction with assignment can be used to put a mapping into a dict. For example, the statement below adds the mapping 'lemon' to 'yellow'.

flora_to_color[ 'lemon' ] = 'yellow'

• The keys of a dict are always distinct. So, the following statement

flora_to_color[ 'potato' ] = 'golden'

would cause flora_to_color to lose its association of mapping potato to brown — its association with 'potato' is now only to golden.

• As our flora_to_color example shows, the values of a dict are not necessarily unique.

• Python dict's have functions keys() and values() for getting a hold of keys and values.

the_keys = flora_to_color.keys()

the_values = flora_to_color.values()

While there are never any duplicates in the keys, depending upon the dictionary there may be duplicates in the values.

• Other information about dict objects are listed below. In the below, assume that d is a dict.

• d.get(k) returns the value that key k maps to in d. If there is no such value, returns None.

• d[k] returns the value that key k maps to in d. If there is no such value, an exception (error) occurs.

• (k in d) indicates whether k is a key value in d.

• (k not in d) indicates whether k is not a key value in d.

• d.clear() removes all mappings in d.

• del d[k] removes k’s mapping in d.

• Information on a dict is available in the module documentation section of the website.

• Additional information on collections is in general is available in the collections epistile.

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Problem even_odd.py

• Introduce the Python dict data structure

Some program runs

Enter a number: 3

3 odd

Enter even or odd: even

a number is even if its remainder divided by 2 is 0

Enter a number: 6

6 even

Enter even or odd: odd

a number is odd if its remainder divided by 2 is 1

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Problem good_doggie.py

• For a series of dog information requests, the program reports what it knows about the dog.

• Its dog information data source is located at URL

http://www.cs.virginia.edu/~cs1112/datasets/csv/puppies.csv

• Brainstorming

• How should we store the dog information?

• How do we get and store the input?

• How many times do we set up the dog information

• What times of loops do we need?

• Sequential

• Nested

• Mixture of nested and sequential

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Where am I

 

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