This Week

1
This Week

• while loops
• Using the debugger
• Dictionaries
• not exactly Websters
• Midterm Questions

in Wing
in PPT then wing
2
Dictionaries

• Generalize the concept were used to.
• Have a key value pair
• Websters Dictionary
• key word
• value definition of word
• Use the key to locate the corresponding value
• Say the key indexes into the dictionary
• Keys are unique.

3
Dictionary Examples

• Student grades file
• key student number, value grade
• GDP for Canada since 1900
• key year, value GDP
• Growth rate of fruit flies
• key time, value number of fruit flies

4
Dictionaries and Python

• dictionary_name key1 value1, key2 value2,
  
• Example
• N. American fossil fuel emissions by year
• Units are 1000s of metric tons of carbon
• emissions 1799 1, 1800 70, 1801 74, 1802
  82,
• 1902 215630, 2002 1733297
• Look up entry
• emissions1902 or emissions.get(1902)
• Add entry
• emissions1950 734914
• Delete entry
• del emissions1902
• Check for membership
• 1950 in emissions

5
More Dictionary Operations

• Looping over dictionaries
• for key in emissions
• print key , emissionskey
• Create a list of keys
• emissions.keys() 1799, 1800, 1801, 1802,
  1902, 2002
• Create a list of values
• emissions.values() 1, 70, 74, 82, 215630,
  1733297
• Create a list of (key, value) pairs
• emissions.items() (1799, 1), (1800, 70),
  (1801, 74), (1802, 82), (1902, 215630), (2002,
  1733297)

6
More Dictionary Operations

• emissions 1799 1, 1800 70, 1801 74, 1802
  82, 1902 215630, 2002 1733297
• emissions2 1850 5418, 1875 37561, 1925
  486728, 1950 735036, 2004 1824421
• Add the contents of one dictionary to another
• emissions.update(emissions2)
• emissions is
• 1799 1, 1800 70, 1801 74, 1802 82,
  1902 215630, 2002 1733297, 1925 486728,
  1950 735036, 2004 1824421, 1850 5418, 1875
  37561
• Clear the contents of a dictionary
• emissions2.clear()