Introduction to Computation and Programming Using Python, Revided & Expanded

315 Pages·2013·13.431 MB·English

by  John V. Guttag

Introduction to
Computation and
Programming Using Python

Introduction to
Computation and
Programming Using Python

Revised and Expanded Edition

John V. Guttag

The MIT Press
Cambridge, Massachusetts
London, England
©
 2013
 Massachusetts Institute of Technology

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Library
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 Cataloging-­‐in-­‐Publication
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Guttag,
 John.

Introduction
 to
 computation
 and
 programming
 using
 Python
 /
 John
 V.
 Guttag.
 —

Revised
 and
 expanded
 edition.

  pages
  cm

Includes
 index.

ISBN
 978-­‐0-­‐262-­‐52500-­‐8
 (pbk.
 :
 alk.
 paper)

1.

 Python
 (Computer
 program
 language)
  2.

 Computer
 programming.
  I.
 Title.

QA76.73.P48G88
  2013

005.13'3—dc23

10
  9
  8
  7
  6
  5
  4
  3
  2
  1
To my family:

Olga
David
Andrea
Michael
Mark
Addie

CONTENTS

PREFACE ....................................................................................................... xiii

ACKNOWLEDGMENTS ..................................................................................... xv

1
  GETTING STARTED .................................................................................... 1

2
  INTRODUCTION TO PYTHON ...................................................................... 7

2.1
  The Basic Elements of Python ............................................................... 8

2.1.1
  Objects, Expressions, and Numerical Types .................................... 9

2.1.2
  Variables and Assignment ............................................................ 11

2.1.3
  IDLE ............................................................................................ 13

2.2
  Branching Programs ........................................................................... 14

2.3
  Strings and Input ............................................................................... 16

2.3.1
  Input ............................................................................................ 18

2.4
  Iteration .............................................................................................. 18

3
  SOME SIMPLE NUMERICAL PROGRAMS .................................................. 21

3.1
  Exhaustive Enumeration .................................................................... 21

3.2
  For Loops ............................................................................................ 23

3.3
  Approximate Solutions and Bisection Search ...................................... 25

3.4
  A Few Words About Using Floats ........................................................ 29

3.5
  Newton-Raphson ................................................................................ 32

4
  FUNCTIONS, SCOPING, and ABSTRACTION ............................................. 34

4.1
  Functions and Scoping ....................................................................... 35

4.1.1
  Function Definitions ..................................................................... 35

4.1.2
  Keyword Arguments and Default Values ....................................... 36

4.1.3
  Scoping ........................................................................................ 37

4.2
  Specifications ..................................................................................... 41

4.3
  Recursion ........................................................................................... 44

4.3.1
  Fibonacci Numbers ...................................................................... 45

4.3.2
  Palindromes ................................................................................. 48

4.4
  Global Variables ................................................................................. 50

4.5
  Modules .............................................................................................. 51

4.6
  Files ................................................................................................... 53
viii
(cid:3) (cid:3)
5 STRUCTURED TYPES, MUTABILITY, AND HIGHER-ORDER FUNCTIONS .. 56
(cid:3) (cid:3)
5.1 Tuples ................................................................................................ 56
(cid:3) (cid:3)
5.1.1 Sequences and Multiple Assignment ............................................. 57
(cid:3) (cid:3)
5.2 Lists and Mutability ............................................................................ 58
(cid:3) (cid:3)
5.2.1 Cloning ........................................................................................ 63
(cid:3) (cid:3)
5.2.2 List Comprehension ..................................................................... 63
(cid:3) (cid:3)
5.3 Functions as Objects .......................................................................... 64
(cid:3) (cid:3)
5.4 Strings, Tuples, and Lists ................................................................... 66
(cid:3) (cid:3)
5.5 Dictionaries ........................................................................................ 67
(cid:3) (cid:3)
6 TESTING AND DEBUGGING. ..................................................................... 70
(cid:3) (cid:3)
6.1 Testing ................................................................................................ 70
(cid:3) (cid:3)
6.1.1 Black-Box Testing ........................................................................ 71
(cid:3) (cid:3)
6.1.2 Glass-Box Testing ........................................................................ 73
(cid:3) (cid:3)
6.1.3 Conducting Tests ......................................................................... 74
(cid:3) (cid:3)
6.2 Debugging .......................................................................................... 76
(cid:3) (cid:3)
6.2.1 Learning to Debug ........................................................................ 78
(cid:3) (cid:3)
6.2.2 Designing the Experiment ............................................................ 79
(cid:3) (cid:3)
6.2.3 When the Going Gets Tough ......................................................... 81
(cid:3) (cid:3)
6.2.4 And When You Have Found “The” Bug .......................................... 82
(cid:3) (cid:3)
7 EXCEPTIONS AND ASSERTIONS .............................................................. 84
(cid:3) (cid:3)
7.1 Handling Exceptions ........................................................................... 84
(cid:3) (cid:3)
7.2 Exceptions as a Control Flow Mechanism ........................................... 87
(cid:3) (cid:3)
7.3 Assertions ........................................................................................... 90
(cid:3) (cid:3)
8 CLASSES AND OBJECT-ORIENTED PROGRAMMING ............................... 91
(cid:3) (cid:3)
8.1 Abstract Data Types and Classes ........................................................ 91
(cid:3) (cid:3)
8.1.1 Designing Programs Using Abstract Data Types ............................ 96
(cid:3) (cid:3)
8.1.2 Using Classes to Keep Track of Students and Faculty ................... 96
(cid:3) (cid:3)
8.2 Inheritance ......................................................................................... 99
(cid:3) (cid:3)
8.2.1 Multiple Levels of Inheritance ..................................................... 101
(cid:3) (cid:3)
8.2.2 The Substitution Principle .......................................................... 102
(cid:3) (cid:3)
8.3 Encapsulation and Information Hiding .............................................. 103
(cid:3) (cid:3)
8.3.1 Generators ................................................................................. 106
(cid:3) (cid:3)
8.4 Mortgages, an Extended Example ..................................................... 108
ix
9
  A SIMPLISTIC INTRODUCTION TO ALGORITHMIC COMPLEXITY ............ 113

9.1
  Thinking About Computational Complexity ....................................... 113

9.2
  Asymptotic Notation .......................................................................... 116

9.3
  Some Important Complexity Classes ................................................. 118

9.3.1
  Constant Complexity .................................................................. 118

9.3.2
  Logarithmic Complexity .............................................................. 118

9.3.3
  Linear Complexity ...................................................................... 119

9.3.4
  Log-Linear Complexity ................................................................ 120

9.3.5
  Polynomial Complexity ............................................................... 120

9.3.6
  Exponential Complexity .............................................................. 121

9.3.7
  Comparisons of Complexity Classes ............................................ 123

10
  SOME SIMPLE ALGORITHMS AND DATA STRUCTURES ......................... 125

10.1
  Search Algorithms .......................................................................... 126

10.1.1
  Linear Search and Using Indirection to Access Elements .......... 126

10.1.2
  Binary Search and Exploiting Assumptions .............................. 128

10.2
  Sorting Algorithms .......................................................................... 131

10.2.1
  Merge Sort ................................................................................ 132

10.2.2
  Exploiting Functions as Parameters .......................................... 135

10.2.3
  Sorting in Python ..................................................................... 136

10.3
  Hash Tables .................................................................................... 137

11
  PLOTTING AND MORE ABOUT CLASSES ................................................ 141

11.1
  Plotting Using PyLab ....................................................................... 141

11.2
  Plotting Mortgages, an Extended Example ....................................... 146

12
  STOCHASTIC PROGRAMS, PROBABILITY, AND STATISTICS ................... 152

12.1
  Stochastic Programs ....................................................................... 153

12.2
  Inferential Statistics and Simulation ............................................... 155

12.3
  Distributions .................................................................................. 166

12.3.1
  Normal Distributions and Confidence Levels ............................. 168

12.3.2
  Uniform Distributions .............................................................. 170

12.3.3
  Exponential and Geometric Distributions ................................. 171

12.3.4
  Benford’s Distribution .............................................................. 173

12.4
  How Often Does the Better Team Win? ............................................ 174

12.5
  Hashing and Collisions ................................................................... 177