In-class notes for 03/17/2014

CS 121B (CS1), Spring 2014

• Homework assignment

• Quiz returned

  Problem 1, Problem 2

Exercise

• An atom in a list is an element of that list or one of its sublists that is not a non-empty list. Examples:

      ['ab', 3, [14, True]]     has four atoms (but 3 elements)
  
      [['x', -1.1, [6, 0], 2], 'y', []]  has 7 atoms (3 elements)
  
      [[[], -1.1, [6, 0], 2], 'y', []]   also has 7 atoms (3 elements)
  
      [[]]     has one atom, (and one element) an empty list
  

  Exercise: Write a function that counts the number of atoms in a list, using recursion

  countAtoms One argument: Any (possibly nested) Python3 list Return: A non-negative integer, the number of atoms in that list arg1

  Example calls:

      countAtoms(['ab', 3, [14, True]]) --> 4
      countAtoms([[14, True], 'ab', 3]) --> 4
      countAtoms([]) --> 0
  

  Hints:

  • Start by writing down the cases

  • Then write a "framework" function definition that includes guards for cases, but no code for what to compute in those cases. Include "assert" comments.

  • Then, fill in the code for computing those cases. Look for opportunities for recursive calls with smaller data, reasoning from the spec.

• Solution

Submitted questions on assignments and technology

• Files on the Link computers

Upcoming

• Homework 16

• Quiz on Wednesday. See below for topics.

Summary of strings chapter

Files

• open()

• Traversing line-by-line with a for loop

• Methods close(), read(), write()

Dictionaries

Submitted questions on readings

To study for quiz

• Trees: list representations; (non-recursive) functions such as problem 12

• Strings, including Strings problem 1:

  • Methods: split(), lower(), strip()

  • Traversing a string ("approach 1" or "approach 2"), as in HW12A

  • Reading from input and/or argument string/list of strings

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