Advanced scripting programming

1
Advanced scripting programming

• jesus.ibanez_at_upf.edu

2
Built-in data types
3
Generality

• In general
• Lists, dictionaries, and tuples can hold any kind
  of object.
• Lists, dictionaries, and tuples can be
  arbitrarily nested.
• Lists and dictionaries can dynamically grow and
  shrink.

4
Generality

• gtgtgt L 'abc', (1, 2), (3, 4), 5
• gtgtgt L1
• (1, 2), (3, 4)
• gtgtgt L11
• (3, 4)
• gtgtgt L110
• 3
• gtgtgt L1100
• 3

5
Shared references

• Assignments store references to objects, not
  copies.
• gtgtgt X 1, 2, 3
• gtgtgt L 'a', X, 'b'
• gtgtgt D 'x'X, 'y'2

6
Shared references

• Since lists are mutable...
• gtgtgt X1 'surprise' changes all three
  references!
• gtgtgt L
• 'a', 1, 'surprise', 3, 'b'
• gtgtgt D
• 'x' 1, 'surprise', 3, 'y' 2

7
Comparisons, Equality, and Truth

• gtgtgt L1 1, ('a', 3) same value,
  unique objects
• gtgtgt L2 1, ('a', 3)
• gtgtgt L1 L2, L1 is L2 equivalent?,
  same object?
• (1, 0)
• The operator tests value equivalence
• The is operator tests object identity

8
Comparisons, Equality, and Truth

• gtgtgt L1 1, ('a', 3)
• gtgtgt L2 1, ('a', 2)
• gtgtgt L1 lt L2, L1 L2, L1 gt L2 less, equal,
  greater a tuple of results
• (0, 0, 1)

9
Comparisons, Equality, and Truth

• In general, Python compares the types we've seen
  as follows
• Numbers are compared by relative magnitude.
• Strings are compared lexicographically,
  character-by-character ("abc" lt "ac").
• Lists and tuples are compared by comparing each
  component, from left to right.

10
Special cases

• Assignment creates references, not copies
• gtgtgt L 1, 2, 3
• gtgtgt M 'X', L, 'Y' embed a reference
  to L
• gtgtgt M
• 'X', 1, 2, 3, 'Y'
• gtgtgt L1 0 changes M too
• gtgtgt M
• 'X', 1, 0, 3, 'Y'

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Special cases

• solution
• gtgtgt L 1, 2, 3
• gtgtgt M 'X', L, 'Y' embed a copy of L
• gtgtgt L1 0 only changes L,
  not M
• gtgtgt L
• 1, 0, 3
• gtgtgt M
• 'X', 1, 2, 3, 'Y'

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Special cases

• Repetition
• gtgtgt L 4, 5, 6
• gtgtgt X L 4 like 4, 5, 6 4, 5,
  6 ...
• gtgtgt Y L 4 L L ... L,
  L,...
• gtgtgt X
• 4, 5, 6, 4, 5, 6, 4, 5, 6, 4, 5, 6
• gtgtgt Y
• 4, 5, 6, 4, 5, 6, 4, 5, 6, 4, 5, 6

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Special cases

• gtgtgt L1 0 impacts Y but not X
• gtgtgt X
• 4, 5, 6, 4, 5, 6, 4, 5, 6, 4, 5, 6
• gtgtgt Y
• 4, 0, 6, 4, 0, 6, 4, 0, 6, 4, 0, 6
• solution
• gtgtgt Y L 4
• instead of
• gtgtgt Y L 4

14
Special cases

• Immutable types can't be changed in place
• T (1, 2, 3)
• T2 4 error!
• T T2 (4,) okay (1, 2, 4)