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Python for Computational Science and Engineering

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Python for Computational Science and Engineering Introduction to Python for Computational Science and Engineering (A beginner's guide) Hans Fangohr Faculty of Engineering and the Environment University of Southampton September 7, 2015 2 Contents 1 Introduction 9 1.1 Computational Modelling . .9 1.1.1 Introduction . .9 1.1.2 Computational Modelling . .9 1.1.3 Programming to support computational modelling . 10 1.2 Why Python for scientific computing? . 11 1.2.1 Optimisation strategies . 12 1.2.2 Get it right first, then make it fast . 13 1.2.3 Prototyping in Python . 13 1.3 Literature . 13 1.3.1 Recorded video lectures on Python for beginners . 13 1.3.2 Python tutor mailing list . 14 1.4 Python version . 14 1.5 This document . 14 1.6 Your feedback . 14 2 A powerful calculator 17 2.1 Python prompt and Read-Eval-Print Loop (REPL) . 17 2.2 Calculator . 17 2.3 Integer division . 18 2.3.1 How to avoid integer division . 18 2.3.2 Why should I care about this division problem? . 19 2.4 Mathematical functions . 20 2.5 Variables . 21 2.5.1 Terminology . 22 2.6 Impossible equations . 22 2.6.1 The += notation . 23 3 Data Types and Data Structures 25 3.1 What type is it? . 25 3.2 Numbers . 25 3.2.1 Integers . 25 3.2.2 Long integers . 26 3.2.3 Floating Point numbers . 26 3.2.4 Complex numbers . 27 3.2.5 Functions applicable to all types of numbers . 27 3.3 Sequences . 27 3.3.1 Sequence type 1: String . 28 3.3.2 Sequence type 2: List . 29 3.3.3 Sequence type 3: Tuples . 31 3 4 CONTENTS 3.3.4 Indexing sequences . 32 3.3.5 Slicing sequences . 33 3.3.6 Dictionaries . 35 3.4 Passing arguments to functions . 37 3.4.1 Call by value . 37 3.4.2 Call by reference . 38 3.4.3 Argument passing in Python . 39 3.4.4 Performance considerations . 40 3.4.5 Inadvertent modification of data . 41 3.4.6 Copying objects . 42 3.5 Equality and Identity/Sameness . 42 3.5.1 Equality . 42 3.5.2 Identity / Sameness . 43 3.5.3 Example: Equality and identity . 43 4 Introspection 45 4.1 dir() . 45 4.1.1 Magic names . 46 4.2 type .............................................. 46 4.3 isinstance . 47 4.4 help . 47 4.5 Docstrings . 49 5 Input and Output 51 5.1 Printing to standard output (normally the screen) . 51 5.1.1 Simple print (not compatible with Python 3.x) . 51 5.1.2 Formatted printing . 52 5.1.3 \str" and \ str ".................................. 53 5.1.4 \repr" and \ repr "................................. 53 5.1.5 Changes from Python 2 to Python 3: print .................... 54 5.1.6 Changes from Python 2 to Python 3: formatting of strings . 54 5.2 Reading and writing files . 55 5.2.1 File reading examples . 56 6 Control Flow 59 6.1 Basics . 59 6.1.1 Conditionals . 59 6.2 If-then-else . 61 6.3 For loop . 61 6.4 While loop . 62 6.5 Relational operators (comparisons) in if and while statements . 62 6.6 Exceptions . 63 6.6.1 Raising Exceptions . 64 6.6.2 Creating our own exceptions . 65 6.6.3 LBYL vs EAFP . 65 7 Functions and modules 67 7.1 Introduction . 67 7.2 Using functions . 67 7.3 Defining functions . 68 7.4 Default values and optional parameters . 70 CONTENTS 5 7.5 Modules . 71 7.5.1 Importing modules . 71 7.5.2 Creating modules . 72 7.5.3 Use of name .................................... 73 7.5.4 Example 1 . 73 7.5.5 Example 2 . 74 8 Functional tools 77 8.1 Anonymous functions . 77 8.2 Map.............................................. 78 8.3 Filter . 78 8.4 List comprehension . 79 8.5 Reduce . 80 8.6 Why not just use for-loops? . 82 8.7 Speed . 83 9 Common tasks 85 9.1 Many ways to compute a series . 85 9.2 Sorting . 88 10 From Matlab to Python 91 10.1 Important commands . 91 10.1.1 The for-loop . ..
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