Table Of ContentModern Python Cookbook
The latest in modern Python recipes
for the busy modern programmer
Steven F. Lott
BIRMINGHAM - MUMBAI
Modern Python Cookbook
Copyright © 2016 Packt Publishing
First published: November 2016
Production reference: 1211116
Published by Packt Publishing Ltd.
Livery Place
35 Livery Street
Birmingham
B3 2PB, UK.
ISBN 978-1-78646-925-0
www.packtpub.com
Contents
Preface
1
Chapter 1: Numbers, Strings, and Tuples
6
Introduction 6
Creating meaningful names and using variables 7
Getting ready 7
How to do it… 8
Choosing names wisely 8
Assigning names to objects 10
How it works… 11
There's more… 12
See also 12
Working with large and small integers 13
Getting ready 13
How to do it… 13
How it works… 14
There's more… 16
See also 17
Choosing between float, decimal, and fraction 17
Getting ready 17
How to do it… 18
Doing currency calculations 18
Fraction calculations 19
Floating-point approximations 20
Converting numbers from one type to another 21
How it works… 22
There's more… 23
See also 24
Choosing between true division and floor division 25
Getting ready 25
How to do it… 25
Doing floor division 26
Doing true division 26
Rational fraction calculations 27
How it works… 27
See also 28
Rewriting an immutable string 28
Getting ready 28
How to do it… 29
Slicing a piece of a string 29
Updating a string with a replacement 30
Making a string all lowercase 31
Removing extra punctuation marks 31
How it works… 31
There's more… 33
See also 33
String parsing with regular expressions 34
Getting ready 34
How to do it… 34
How it works… 36
There's more… 37
See also 37
Building complex strings with “template”.format() 38
Getting ready 38
How to do it… 38
How it works… 40
There's more… 42
See also 42
Building complex strings from lists of characters 43
Getting ready 43
How to do it… 44
How it works… 44
There's more 45
See also 46
Using the Unicode characters that aren't on our keyboards 46
Getting ready 46
How to do it… 47
How it works… 47
See also 48
Encoding strings – creating ASCII and UTF-8 bytes 49
Getting ready 49
How to do it… 49
How it works… 50
See also 51
Decoding bytes – how to get proper characters from some bytes 52
Getting ready 52
How to do it.. 53
[ ii ]
How it works… 54
See also 55
Using tuples of items 55
Getting ready 55
How to do it… 55
Creating tuples 56
Extracting items from a tuple 56
How it works… 57
There's more 58
See also… 58
Chapter 2: Statements and Syntax
59
Introduction 59
Writing Python script and module files – syntax basics 60
Getting ready 60
How to do it… 61
How it works… 63
There's more… 64
See also 65
Writing long lines of code 65
Getting ready 66
How to do it… 66
Using backslash to break a long statement into logical lines 67
Using the () characters to break a long statement into sensible pieces 67
Using string literal concatenation 68
Assigning intermediate results to separate variables 69
How it works… 69
There's more… 70
See also 70
Including descriptions and documentation 71
Getting ready 71
How to do it… 72
Writing docstrings for scripts 72
Writing docstrings for library modules 74
How it works… 74
There's more… 75
See also 76
Writing better RST markup in docstrings 76
Getting ready 76
How to do it… 77
How it works… 78
[ iii ]
There's more… 79
Using directives 81
Using inline markup 81
See also 82
Designing complex if…elif chains 82
Getting ready 83
How to do it… 84
How it works… 85
There's more… 86
See also 87
Designing a while statement which terminates properly 87
Getting ready 87
How to do it… 88
How it works… 91
See also 92
Avoiding a potential problem with break statements 93
Getting ready 93
How to do it… 94
How it works… 95
There's more… 96
See also 96
Leveraging the exception matching rules 97
Getting ready 98
How to do it… 99
How it works… 100
There's more… 100
See also 101
Avoiding a potential problem with an except: clause 102
Getting ready 102
How to do it… 102
How it works… 103
See also 103
Chaining exceptions with the raise from statement 104
Getting ready 104
How to do it… 104
How it works… 105
There's more… 106
See also 107
Managing a context using the with statement 107
Getting ready 107
[ iv ]
How to do it… 108
How it works… 109
There's more… 110
See also 110
Chapter 3: Function Definitions
111
Introduction 111
Designing functions with optional parameters 112
Getting ready 112
How to do it… 112
Particular to General Design 113
General to Particular design 115
How it works… 116
There's more… 117
See also 118
Using super flexible keyword parameters 118
Getting ready 119
How to do it… 119
How it works… 121
There's more… 121
See also 122
Forcing keyword-only arguments with the * separator 122
Getting ready 123
How to do it… 124
How it works… 125
There's more… 125
See also 126
Writing explicit types on function parameters 126
Getting ready 127
How to do it… 128
How it works… 129
There's more… 131
See also 132
Picking an order for parameters based on partial functions 132
Getting ready 132
How to do it… 134
Wrapping a function 134
Creating a partial function with keyword parameters 135
Creating a partial function with positional parameters 135
How it works… 136
There's more… 137
[ v ]
See also 137
Writing clear documentation strings with RST markup 137
Getting ready 138
How to do it… 138
How it works… 141
There's more… 142
See also 142
Designing recursive functions around Python's stack limits 142
Getting ready 143
How to do it… 144
How it works… 145
There's more… 146
See also 148
Writing reusable scripts with the script library switch 148
Getting ready 148
How to do it… 149
How it works… 151
There's more… 151
See also 152
Chapter 4: Built-in Data Structures – list, set, dict
153
Introduction 153
Choosing a data structure 154
Getting ready 154
How to do it… 154
How it works… 156
There's more… 158
See also 158
Building lists – literals, appending, and comprehensions 159
Getting ready 159
How to do it… 160
Building a list with the append() method 160
Writing a list comprehension 161
Using the list function on a generator expression 162
How it works… 163
There's more… 163
Other ways to extend a list 164
See also 165
Slicing and dicing a list 165
Getting ready 165
[ vi ]
How to do it… 167
How it works… 169
There's more… 169
See also 170
Deleting from a list – deleting, removing, popping, and filtering 170
Getting ready 170
How to do it… 171
Deleting items from a list 171
The remove() method 172
The pop() method 173
The filter() function 173
How it works… 174
There's more… 175
See also 176
Reversing a copy of a list 176
Getting ready 176
How to do it… 178
How it works… 179
See also 179
Using set methods and operators 179
Getting ready 181
How to do it… 182
How it works… 183
There's more… 184
See also 185
Removing items from a set – remove(), pop(), and difference 186
Getting ready 186
How to do it… 187
How it works… 188
There's more… 188
See also 189
Creating dictionaries – inserting and updating 189
Getting ready 190
How to do it… 191
How it works… 192
There's more… 192
See also 194
Removing from dictionaries – the pop() method and the del statement 194
Getting ready 195
How to do it… 196
[ vii ]
How it works… 197
There's more… 197
See also 197
Controlling the order of dict keys 198
Getting ready 198
How to do it… 199
How it works… 200
There's more… 200
See also 201
Handling dictionaries and sets in doctest examples 201
Getting ready 201
How to do it… 202
How it works… 203
There's more… 203
Understanding variables, references, and assignment 204
How to do it… 204
How it works… 205
There's more… 206
See also 207
Making shallow and deep copies of objects 207
Getting ready 208
How to do it… 209
How it works… 210
See also 211
Avoiding mutable default values for function parameters 211
Getting ready 212
How to do it… 213
How it works… 214
There's more… 215
See also 216
Chapter 5: User Inputs and Outputs
217
Introduction 217
Using features of the print() function 218
Getting ready 218
How to do it… 220
How it works… 221
There's more… 222
See also 223
Using input() and getpass() for user input 223
[ viii ]
