Index

1. Python dictionaries

• recall from our first python lecture that python has a dictionary type

• #!/usr/bin/python
  
  d = {’spam’:2, ’ham’:1, ’eggs’:10}
  
  print d[’eggs’]

• ./py13.py
  10

• can alter the dictionary
  • by adding new entries
  • by changing values
  • by removing entries
• we can test for the presence of an entry within the dictionary

• #!/usr/bin/python
  
  d = {’spam’:2, ’ham’:1, ’eggs’:10}
  print d[’eggs’]
  
  
  d[’eggs’]=12
  d[’bacon’]=1
  print d[’bacon’]
  print d

• ./py14.py
  10
  1
  {’spam’: 2, ’ham’: 1, ’bacon’: 1, ’eggs’: 12}

2. Dictionary initialisation

• we can create an empty dictionary by:

• d = {}

• we can add to a dictionary by:

• d[’foobar’] = 4

3. Dictionary modification

• we can remove an entry via:

• del d[’eggs’]

• we can test whether an item exists in the dictionary

• #!/usr/bin/python
  
  d = {’spam’:2, ’ham’:1, ’eggs’:10}
  
  if d.has_key(’eggs’):
      print ’we have some eggs’
  else:
      print ’we do not have any eggs’
  
  
  if d.has_key(’flour’):
      print ’we have some flour’
  else:
      print ’we do not have any flour’

Index

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