Mercurial > hgrepos > Python > libs > ConfigMix

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Begin the handling of JSON-style configuration files
author Franz Glasner <hg@dom66.de>
date Wed, 04 Apr 2018 09:45:29 +0200
parents c5b638f9c607
children b34ad08e7198
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1 .. -*- coding: utf-8; indent-tabs-mode: nil; -*-
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2
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3 .. _introduction:
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4
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5 Introduction
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6 ============
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7
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8 The configurations can be read from different types of files:
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9
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10 - :ref:`YAML files <yaml-files>`
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11 - :ref:`JSON files <json-files>`
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12 - :ref:`INI files <ini-files>`
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13 - :ref:`executable Python scripts <executable-python-scripts>`
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16 .. _yaml-files:
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17
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18 YAML Files
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19 ----------
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20
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21 Need the :mod:`yaml` package (e.g. ``pip install pyyaml``)
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22
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23 .. note:: All strings are returned as Unicode text strings.
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25
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26 An example is:
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27
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28 .. literalinclude:: ../tests/data/conf10.yml
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29 :language: yaml
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32 .. _json-files:
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33
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34 JSON files
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35 ----------
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36
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37 .. todo:: Document basic JSON usage
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39
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40 .. _ini-files:
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41
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42 INI Files
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43 ---------
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44
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45 Read the file and all sections named in parameter `extract` are flattened
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46 into the resulting dictionary. By default the section named ``config`` is
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47 used.
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48
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49 Normally all values are returned as Unicode text strings.
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50 But values can be annotated and therefore interpreted as other types:
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51
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52 ``:int:``
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53 The value is handled in the same way as a Python :class:`int`
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54 literal
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55
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56 ``:float:``
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57 The value is interpreted as :class:`float`
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58
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59 ``:bool:``
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60 The resulting value is a :class:`bool` where
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61
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62 ``1``, ``true``, ``yes``, ``on``
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63 yield a Python ``True``
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64
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65 ``0``, ``false``, ``no``, ``off``
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66 yield a Python ``False``
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67
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68 The evaluation is done *case-insensitively*.
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69
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70 .. note:: All strings are returned as Unicode text strings.
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71
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72 .. note:: Contrary to the behaviour of the standard Python :mod:`configparser`
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73 module the INI file reader is *case-sensitive*.
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74
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75 The example INI style configuration below yields an equivalent
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76 configuration to the YAML configuration above:
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78 .. literalinclude:: ../tests/data/conf10.ini
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79 :language: ini
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80
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81 As can be seen in thie example -- INI file internal value interpolation
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82 is done as in Python's standard :mod:`configparser` module.
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83
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84 This example also illustrates how INI sections are used to build a
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85 tree-ish configuration dictionary.
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86
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88 .. _executable-python-scripts:
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89
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90 Executable Python Scripts
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91 -------------------------
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92
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93 What will be exported:
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94
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95 1. If loading is done with the `extract` parameter only the given keys are
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96 extracted from the script.
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98 2. Otherwise it is checked if the scripts defines an ``__all__``
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99 sequence. If there is one it's contents are the keys to be
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100 extracted.
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101
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102 3. If there is no ``__all__`` object all names not starting with an
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103 underscore ``_`` are found.
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104
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105 This is analogous to as Python modules behave when importing them with
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106 ``from module import *``.
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107
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108 .. note:: The Python configuration files are evaluated with ``exec`` and not
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109 imported.
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110
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111 The example configuration by Python script below yields an equivalent
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112 configuration to the YAML configuration above:
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113
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114 .. literalinclude:: ../tests/data/conf10.py
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115 :language: python
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116
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117
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118 .. _loading-and-merging:
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119
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120 Loading and Merging
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121 -------------------
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122
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123 Basic usage of the API is as follows in this example::
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124
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125 import configmix
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126
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127 #
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128 # Note: With conf10 merging is rather pointless because the tree
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129 # files # are really the same configuration. But is doesn't harm
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130 # also here.
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131 #
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132 config = configmix.load("conf10.yml", "conf10.ini", "conf10.py")
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133
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134 # Get a -- possibly interpolated -- configuration variable's value
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135 value1 = config.getvar_s("key1")
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136
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137 # Get a -- possibly interpolated -- variable from within the tree
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138 value2 = config.getvar_s("tree1.tree2.key4")
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139
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140
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141 The filenames of the configuration files must have the extensions
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142 (case-insensitively):
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143
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144 ``.py``
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145 for Python configuration files
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146
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147 ``.yml`` or ``.yaml``
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148 for YAML configuration files
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149
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150 ``.json``
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151 for JSON configuration files
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152
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153 ``.ini``
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154 for INI configuration files
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155
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156
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157 .. _getting-values:
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158
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159 Getting configuration variables
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160 -------------------------------
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161
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162 Get a -- possibly expanded -- configuration variable's value with::
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163
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164 value1 = config.getvar_s("key1")
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165
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166 Get a raw configuration variable's value with::
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167
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168 value1_raw = config.getvar("key1")
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169
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170 Because the configuration is not only a plain list of but a tree of
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171 key-value pairs you will want to fetch them by separating the individual
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172 level keys with a point ``.``.
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173
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174 Looking at the example in chapter :ref:`yaml-files` -- when calling
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175 ``config.getvar_s("tree1.tree2.key4")`` you will get the value
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176 ``get this as `tree1.tree2.key4'``.
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177
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178 This is true for both methods :py:meth:`.Configuration.getvar` and
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179 :py:meth:`.Configuration.getvar_s`.
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180
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181 Both methods also perform :ref:`variable-expansion` and handle
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182 :ref:`variable-namespaces`. Filtering is not supported. So -- the
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183 variable name arguments of :py:meth:`.Configuration.getvar` and
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184 :py:meth:`.Configuration.getvar_s` are of the form
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185 ``[namespace:]variable``.
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186
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187
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188 .. _variable-namespaces:
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189
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190 Variable Namespaces
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191 -------------------
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192
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193 Currently there are 4 namespaces:
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194
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195 1. The unnamed namespace (which is also default).
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196
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197 All the configuration variables are part of this namespace.
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198
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199 2. The namespace ``OS``
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200
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201 Available functions:
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202
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203 ``cwd``
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204 Contains the current working directory of the process
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205
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206 3. The namespace ``ENV``
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207
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208 This namespace contains all the environment variables as they are
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209 available from :py:data:`os.environ`.
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210
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211 4. The namespace ``PY``
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212
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213 Contains selected values from the running Python:
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214
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215 ``version``
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216 The return value of :py:func:`platform.python_version`
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217
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218 ``version_maj_min``
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219 Just the major and minor version of the running Python
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220 (``.`` separated)
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221
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222 ``version_maj``
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223 Just the major version of the running Python
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224
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225 ``implementation``
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226 The return value of :py:func:`platform.python_implementation`
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227
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228
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229 Examples
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230 ~~~~~~~~
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231
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232 ::
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233
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234 config.getvar("OS:cwd")
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235
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236 yields the current working directory as :py:func:`os.getcwd` does.
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237
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238
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239 .. _variable-expansion:
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240
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241 Variable Expansion
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242 ------------------
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243
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244 Configuration variable values that are read with
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245 :py:meth:`.Configuration.getvar_s` are subject to variable
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246 expansion. The general syntactic pattern for this is::
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247
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248 {{[namespace:]variable[|filter[|filter...]]}}
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249
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250 I.e.: between double curly braces an optional `namespace` name followed by
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251 a colon ``:``, the `variable` and then zero or more filters, each one
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252 introduced by a pipe symbol ``|``.
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253
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254 Variables are expanded lately at runtime -- exactly when calling
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255 :py:meth:`.Configuration.getvar_s` or :py:meth:`.Configuration.getvar`.
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256
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257
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258 Filter functions
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259 ~~~~~~~~~~~~~~~~
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260
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261 Interpolated values can be processed through a series of filter functions::
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262
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263 {{my.variable|filter1|filter2}}
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264
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265 Available filter functions are:
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266
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267 ``urlquote``
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268
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269 ``saslprep``
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270
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271 ``normpath``
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272
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273 ``abspath``
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274
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275 ``posixpath``
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276
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277 ``lower``
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278
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279 ``upper``
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280
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281
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282 Examples
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283 ~~~~~~~~
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284
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285 ::
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286
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287 {{OS:cwd|posixpath}}
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288
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289 expands to the current working directory as POSIX path: on Windows all
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290 backslashes are replaced by forward slashes.
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291
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292 ::
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293
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294 {{ENV:PATH}}
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295
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296 expands to the current search path from the process environment.
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297
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298 ::
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299
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300 {{PY:version}}
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301
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302 expands to the current running Python version (e.g. ``3.6.4``).
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303
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304 ::
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305
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306 {{PY::implementation|upper}}
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307
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308 expands to something like ``CPYTHON`` when using the standard Python
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309 interpreter written in C.