CS61A-lecture9-sequences

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note › cs61a

sequences

list

python list

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digits = [1, 8, 2, 8]
[2, 7] + digits * 2
pairs = [[10, 20], [30, 40]]

containers

it just search element by element

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>>> 1 in digits
True

for statements

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def count(s, value):
  """count the numberof times that value in sequence s.
  """"

  total, index = 0, 0
  while index < len(s):
    element = s[index]
    if element == value:
      total = total + 1
    index = index + 1
  return total

range

range(1, n) from 1 to n - 1

list comprehesion

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[x * x for x in sets if x % 25 == 0]

lists, Slices & Recursion

expamle

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def sum_list(s):
  """sum the elements of list s.
  """
  if len(s) == 0:
    return 0
  else:
    return s[0] + sum_list(s[1:])

containers

box-and-pointer Notation

the closure property of data types

  1. 操作的结果仍然属于相同的类型
  2. 闭包的强大之处在于：它允许我们构建层级结构（hierarchical structures）。
  3. 层级结构的本质是“部分由部分组成”。
  4. 在 Python 里，列表是一种具有闭包性质的数据结构

box-and-pointer Notation in environment diagrams

slicing

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odds = [3, 5, 7, 9, 11]
[odd[i] for i in range(1, 3)]

precessing container values

there are some build-in function

sequence aggregation

  • `sum(literable [, other])

  • ‘max(literable [, key])