Chapter 6 Lists

1
Chapter 6 Lists

• Dr. Bernard Chen Ph.D.
• University of Central Arkansas
• Spring 2012

2
Lists

• Lists are Pythons most flexible ordered
  collection object type
• Lists can contain any sort of object numbers,
  strings and even other lists

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Lists

• Ordered collections of arbitrary objects
• --- from the functional view, lists are just a
  place to collect other objects
• --- Lists also define a left to right positional
  ordering of the items in the list

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Lists

• Accessed by offset
• --- Just as strings, you can fetch a component
  object out of a list by indexing the list on the
  objects offset
• --- you can also for such tasks as slicing and
  concatenation

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Lists

• Variable length, heterogeneous, arbitrary
  nestable
• --- Unlike strings, list can grow and shrink in
  place
• --- lists may contain any sort of object, not
  just one-character strings (they are
  heterogeneous)

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Lists

• gtgtgt aa An empty list
• gtgtgt aa1,2,3,4 4 items, index 0-3

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List in action

• List respond to the and operations much like
  strings
• gtgtgt aa1,2,3
• gtgtgt bb4,5,6
• gtgtgt aabb
• gtgtgt aa3

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List in action

• Lists also have the function len() to tell the
  size of lists and in function
• gtgtgt aa1,2,3
• gtgtgt len(aa)

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Indexing, Slicing, and Matrixes

• Besides lists are sequences, index and slicing
  work the same way
• gtgtgt aa1,2,3
• gtgtgt aa2
• gtgtgt aa-2
• gtgtgt aa1
• (also try some strings in aa)

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Indexing, Slicing, and Matrixes

• We can also assign lists in a list
• gtgtgt matrix1,2,3,4,5,6,7,8,9
• gtgtgt matrix0
• gtgtgt matrix10
• gtgtgt matrix02

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Changing Lists in-place

• When using a list, you can change its contains b
  assigning to a particular item (offset), or an
  entire section (slice)
• gtgtgt aa1,2,3
• gtgtgt aa04
• gtgtgt aa15,6

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List method calls

• The list append method simply tacks a single item
  onto the end of the list
• gtgtgt aa
• gtgtgt aa.append(1)
• gtgtgt aa.append(2)
• gtgtgt aa.append(3)
• gtgtgt aa.append(4)
• gtgtgt aa.append(5.0)

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List method calls

• The sort function orders a list in place (in
  ascending fashion)
• gtgtgt aa4,2,6,8,1,3,4,10
• gtgtgt aa.sort()
• (also try strings in lists)

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List method calls

• reverse reverse the list in-place
• gtgtgt aa1,2,3,4
• gtgtgt aa.reverse()

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List method calls

• del can used to delete an item or section
• gtgtgt aa1,2,3,4,5,6
• gtgtgt del aa0
• gtgtgt del aa2

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In Class Practice

• gtgtgt a1,2,3
• gtgtgt b4,5,6
• gtgtgt bba
• gtgtgt b
• gtgtgt b.sort()
• gtgtgt b
• gtgtgt b.append(7)
• gtgtgt b

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In Class Practice

• gtgtgt a1,2,3
• gtgtgt b4,5,6
• gtgtgt c7,8,9,10
• gtgtgt array
• gtgtgt array.append(a)
• gtgtgt array.append(b)
• gtgtgt array.append(c)
• gtgtgt array2
• gtgtgt array00
• gtgtgt array23