Initial intro doc.
David Wilson
8 years ago
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d457c20d87
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API Reference
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=============
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econtext.core
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#############
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.. automodule:: econtext.core
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:members:
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:undoc-members:
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econtext.master
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###############
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.. automodule:: econtext.master
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:members:
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:undoc-members:
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@ -1,285 +1,22 @@
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# -*- coding: utf-8 -*-
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#
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# econtext documentation build configuration file, created by
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# sphinx-quickstart on Thu Aug 11 18:16:36 2016.
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#
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# This file is execfile()d with the current directory set to its
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# containing dir.
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#
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# Note that not all possible configuration values are present in this
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# autogenerated file.
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#
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# All configuration values have a default; values that are commented out
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# serve to show the default.
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import sys
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import os
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# If extensions (or modules to document with autodoc) are in another directory,
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# add these directories to sys.path here. If the directory is relative to the
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# documentation root, use os.path.abspath to make it absolute, like shown here.
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#sys.path.insert(0, os.path.abspath('.'))
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# -- General configuration ------------------------------------------------
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# If your documentation needs a minimal Sphinx version, state it here.
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#needs_sphinx = '1.0'
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# Add any Sphinx extension module names here, as strings. They can be
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# extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
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# ones.
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extensions = [
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'sphinx.ext.autodoc',
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]
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# Add any paths that contain templates here, relative to this directory.
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templates_path = ['_templates']
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# The suffix(es) of source filenames.
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# You can specify multiple suffix as a list of string:
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# source_suffix = ['.rst', '.md']
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source_suffix = '.rst'
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# The encoding of source files.
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#source_encoding = 'utf-8-sig'
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# The master toctree document.
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master_doc = 'index'
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# General information about the project.
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project = u'econtext'
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copyright = u'2016, David Wilson'
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author = u'David Wilson'
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# The version info for the project you're documenting, acts as replacement for
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# |version| and |release|, also used in various other places throughout the
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# built documents.
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#
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# The short X.Y version.
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version = u'master'
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# The full version, including alpha/beta/rc tags.
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release = u'master'
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# The language for content autogenerated by Sphinx. Refer to documentation
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# for a list of supported languages.
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#
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# This is also used if you do content translation via gettext catalogs.
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# Usually you set "language" from the command line for these cases.
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language = None
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# There are two options for replacing |today|: either, you set today to some
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# non-false value, then it is used:
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#today = ''
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# Else, today_fmt is used as the format for a strftime call.
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#today_fmt = '%B %d, %Y'
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# List of patterns, relative to source directory, that match files and
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# directories to ignore when looking for source files.
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copyright = u'2016, David Wilson'
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exclude_patterns = ['_build']
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# The reST default role (used for this markup: `text`) to use for all
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# documents.
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#default_role = None
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# If true, '()' will be appended to :func: etc. cross-reference text.
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#add_function_parentheses = True
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# If true, the current module name will be prepended to all description
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# unit titles (such as .. function::).
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#add_module_names = True
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# If true, sectionauthor and moduleauthor directives will be shown in the
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# output. They are ignored by default.
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#show_authors = False
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# The name of the Pygments (syntax highlighting) style to use.
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pygments_style = 'sphinx'
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# A list of ignored prefixes for module index sorting.
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#modindex_common_prefix = []
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# If true, keep warnings as "system message" paragraphs in the built documents.
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#keep_warnings = False
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# If true, `todo` and `todoList` produce output, else they produce nothing.
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todo_include_todos = False
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# -- Options for HTML output ----------------------------------------------
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# The theme to use for HTML and HTML Help pages. See the documentation for
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# a list of builtin themes.
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html_theme = 'alabaster'
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# Theme options are theme-specific and customize the look and feel of a theme
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# further. For a list of options available for each theme, see the
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# documentation.
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#html_theme_options = {}
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# Add any paths that contain custom themes here, relative to this directory.
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#html_theme_path = []
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# The name for this set of Sphinx documents. If None, it defaults to
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# "<project> v<release> documentation".
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#html_title = None
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# A shorter title for the navigation bar. Default is the same as html_title.
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#html_short_title = None
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# The name of an image file (relative to this directory) to place at the top
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# of the sidebar.
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#html_logo = None
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# The name of an image file (within the static path) to use as favicon of the
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# docs. This file should be a Windows icon file (.ico) being 16x16 or 32x32
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# pixels large.
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#html_favicon = None
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# Add any paths that contain custom static files (such as style sheets) here,
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# relative to this directory. They are copied after the builtin static files,
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# so a file named "default.css" will overwrite the builtin "default.css".
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extensions = ['sphinx.ext.autodoc']
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html_show_sourcelink = False
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html_show_sphinx = False
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html_sidebars = {'**': ['globaltoc.html']}
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html_static_path = ['_static']
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# Add any extra paths that contain custom files (such as robots.txt or
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# .htaccess) here, relative to this directory. These files are copied
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# directly to the root of the documentation.
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#html_extra_path = []
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# If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
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# using the given strftime format.
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#html_last_updated_fmt = '%b %d, %Y'
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# If true, SmartyPants will be used to convert quotes and dashes to
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# typographically correct entities.
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#html_use_smartypants = True
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# Custom sidebar templates, maps document names to template names.
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#html_sidebars = {}
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# Additional templates that should be rendered to pages, maps page names to
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# template names.
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#html_additional_pages = {}
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# If false, no module index is generated.
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#html_domain_indices = True
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# If false, no index is generated.
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#html_use_index = True
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# If true, the index is split into individual pages for each letter.
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#html_split_index = False
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# If true, links to the reST sources are added to the pages.
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#html_show_sourcelink = True
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# If true, "Created using Sphinx" is shown in the HTML footer. Default is True.
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#html_show_sphinx = True
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# If true, "(C) Copyright ..." is shown in the HTML footer. Default is True.
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#html_show_copyright = True
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# If true, an OpenSearch description file will be output, and all pages will
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# contain a <link> tag referring to it. The value of this option must be the
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# base URL from which the finished HTML is served.
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#html_use_opensearch = ''
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# This is the file name suffix for HTML files (e.g. ".xhtml").
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#html_file_suffix = None
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# Language to be used for generating the HTML full-text search index.
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# Sphinx supports the following languages:
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# 'da', 'de', 'en', 'es', 'fi', 'fr', 'hu', 'it', 'ja'
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# 'nl', 'no', 'pt', 'ro', 'ru', 'sv', 'tr'
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#html_search_language = 'en'
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# A dictionary with options for the search language support, empty by default.
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# Now only 'ja' uses this config value
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#html_search_options = {'type': 'default'}
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# The name of a javascript file (relative to the configuration directory) that
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# implements a search results scorer. If empty, the default will be used.
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#html_search_scorer = 'scorer.js'
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# Output file base name for HTML help builder.
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html_theme = 'alabaster'
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htmlhelp_basename = 'econtextdoc'
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# -- Options for LaTeX output ---------------------------------------------
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latex_elements = {
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# The paper size ('letterpaper' or 'a4paper').
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#'papersize': 'letterpaper',
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# The font size ('10pt', '11pt' or '12pt').
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#'pointsize': '10pt',
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# Additional stuff for the LaTeX preamble.
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#'preamble': '',
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# Latex figure (float) alignment
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#'figure_align': 'htbp',
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}
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# Grouping the document tree into LaTeX files. List of tuples
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# (source start file, target name, title,
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# author, documentclass [howto, manual, or own class]).
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latex_documents = [
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(master_doc, 'econtext.tex', u'econtext Documentation',
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u'David Wilson', 'manual'),
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]
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# The name of an image file (relative to this directory) to place at the top of
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# the title page.
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#latex_logo = None
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# For "manual" documents, if this is true, then toplevel headings are parts,
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# not chapters.
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#latex_use_parts = False
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# If true, show page references after internal links.
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#latex_show_pagerefs = False
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# If true, show URL addresses after external links.
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#latex_show_urls = False
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# Documents to append as an appendix to all manuals.
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#latex_appendices = []
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# If false, no module index is generated.
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#latex_domain_indices = True
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# -- Options for manual page output ---------------------------------------
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# One entry per manual page. List of tuples
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# (source start file, name, description, authors, manual section).
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man_pages = [
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(master_doc, 'econtext', u'econtext Documentation',
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[author], 1)
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]
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# If true, show URL addresses after external links.
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#man_show_urls = False
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# -- Options for Texinfo output -------------------------------------------
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# Grouping the document tree into Texinfo files. List of tuples
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# (source start file, target name, title, author,
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# dir menu entry, description, category)
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texinfo_documents = [
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(master_doc, 'econtext', u'econtext Documentation',
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author, 'econtext', 'One line description of project.',
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'Miscellaneous'),
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]
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# Documents to append as an appendix to all manuals.
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#texinfo_appendices = []
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# If false, no module index is generated.
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#texinfo_domain_indices = True
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# How to display URL addresses: 'footnote', 'no', or 'inline'.
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#texinfo_show_urls = 'footnote'
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# If true, do not generate a @detailmenu in the "Top" node's menu.
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#texinfo_no_detailmenu = False
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language = None
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master_doc = 'index'
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project = u'econtext'
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pygments_style = 'sphinx'
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release = u'master'
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source_suffix = '.rst'
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templates_path = ['_templates']
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todo_include_todos = False
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version = u'master'
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@ -0,0 +1,5 @@
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Getting Started
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===============
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xxx
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@ -0,0 +1,7 @@
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How econtext Works
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------------------
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blah blah
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@ -1,22 +1,209 @@
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.. econtext documentation master file, created by
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sphinx-quickstart on Thu Aug 11 18:16:36 2016.
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You can adapt this file completely to your liking, but it should at least
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contain the root `toctree` directive.
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Welcome to econtext's documentation!
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====================================
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Python Execution Contexts
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=========================
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Contents:
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**4.98KiB of sugar and no fat!**
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.. toctree::
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:maxdepth: 2
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:maxdepth: 1
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self
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howitworks
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getting_started
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api
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Indices and tables
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==================
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Introduction
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------------
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* :ref:`genindex`
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* :ref:`modindex`
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* :ref:`search`
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The Python ``econtext`` package implements external *execution contexts*: an
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execution context is somewhere you can run Python code external to your main
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process, even on a remote machine.
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**There is no requirement for installing packages, copying files around,
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writing shell scripts, upfront configuration, or providing any secondary link
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to the remote machine**. Due to the origins of econtext for use in managing
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potentially damaged infrastructure, the remote machine need not even have a
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writeable filesystem.
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It is not intended as a generic RPC framework, the goal is to provide a robust
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and efficient low-level API on which tools like **Salt** or **Ansible** can be
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built, and while the API is quite friendly and similar in scope to **Fabric**,
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ultimately it should not be used directly by consumer software.
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The primary focus is to centralize and perfect the intricate dance required to
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run Python code safely and efficiently on a remote machine, while avoiding
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temporary files or large chunks of error-prone shell scripts.
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Automatic Bootstrap
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###################
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The package's main feature is enabling your Python program to bootstrap and
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communicate with new Python programs under its control running on remote
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machines, **using only an existing installed Python interpreter and SSH
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client**, something that by default can be found on almost all contemporary
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machines in the wild. To accomplish bootstrap, econtext uses a single 500 byte
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SSH command line and 5KB of data sent to stdin of the remote SSH connection.
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.. code::
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$ python preamble_size.py
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SSH command size: 411
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Preamble size: 5098 (4.98KiB)
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econtext.master size: 2403 (2.35KiB)
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Once bootstrapped, the remote process is configured with a customizable
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**argv[0]**, readily visible to system administrators of the remote machine
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using the UNIX **ps** command:
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.. code::
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20051 ? Ss 0:00 \_ sshd: dmw [priv]
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20053 ? S 0:00 | \_ sshd: dmw@notty
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20054 ? Ssl 0:00 | \_ econtext:dmw@Eldil.home:22476
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20103 ? S 0:00 | \_ tar zxvf myapp.tar.gz
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The example context was started by UID ``dmw`` on host ``Eldil.home``, process
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ID ``22476``.
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IO Multiplexer
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##############
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The bootstrap includes a compact IO multiplexer (like Twisted or asyncio) that
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allows it to perform work in the background while executing your program's
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code. For example, the remote context can be used to connect to a new user on
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the remote machine using **sudo**, or as an intermediary for extending the
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program's domain of control outward to other machines, enabling your program to
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manipulate machines behind a firewall, or to allow its data plane to match your
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network topology.
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The multiplexer also ensures the remote process is terminated if your Python
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program crashes, communication is lost, or the application code running in the
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context has hung.
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Module Forwarder
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################
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In addition to an IO multiplexer, the external context is configured with a
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custom **PEP-302 importer** that forwards requests for unknown Python modules
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back to the host machine. When your program asks an external context to execute
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code from an unknown module, all requisite modules are transferred
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automatically and imported entirely in RAM without need for further
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configuration.
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.. code-block:: python
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import myapp.mypkg.mymodule
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# myapp/__init__.py, myapp/mypkg/__init__.py, and myapp/mypkg/mymodule.py
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# are transferred automatically.
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print context.call(myapp.mymodule.my_function)
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Logging Forwarder
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#################
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The 5KB bootstrap configures the remote process's Python logging package to
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forward all logs back to the local process, enabling management of program logs
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in one location.
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.. code::
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18:15:29 D econtext.ctx.k3: econtext: SlaveModuleImporter.find_module('econtext.zlib')
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18:15:29 D econtext.ctx.k3: econtext: _dispatch_calls((1002L, False, 'posix', None, 'system', ('ls -l /proc/self/fd',), {}))
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Stdio Forwarder
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###############
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To ease porting of crusty old infrastructure code to pure Python, the bootstrap
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redirects stdio for itself and any child processes back into the logging
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framework. This allows use of functions as basic as **os.system('hostname;
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uptime')** without further need to capture or manage output.
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.. code::
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18:17:28 D econtext.ctx.k3: econtext: _dispatch_calls((1002L, False, 'posix', None, 'system', ('hostname; uptime',), {}))
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18:17:56 I econtext.ctx.k3: stdout: k3
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18:17:56 I econtext.ctx.k3: stdout: 17:37:10 up 562 days, 2:25, 5 users, load average: 1.24, 1.13, 1.14
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Blocking Code Friendly
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######################
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Within each process, a private thread runs the I/O multiplexer, leaving the
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main thread and any additional application threads free to perform useful work.
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While econtext is internally asynchronous, it hides this asynchrony from
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consumer code. This is since writing asynchronous code is mostly a foreign
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concept to the target application of managing infrastructure. It should be
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||||
possible to rewrite a shell script in Python without significant restructuring,
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||||
or mind-bending feats of comprehension to understand control flow.
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Before:
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||||
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||||
.. code-block:: sh
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#!/bin/bash
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# Install our application.
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|
||||
tar zxvf app.tar.gz
|
||||
|
||||
After:
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
def install_app():
|
||||
"""
|
||||
Install our application.
|
||||
"""
|
||||
os.system('tar zxvf app.tar.gz')
|
||||
|
||||
context.call(install_app)
|
||||
|
||||
Exceptions raised by function calls are propagated back to the parent program,
|
||||
and timeouts can be configured to ensure failed calls do not block progress of
|
||||
the parent.
|
||||
|
||||
|
||||
Event-driven IO
|
||||
###############
|
||||
|
||||
Code running in a remote context can be connected to a *Channel*. Channels are
|
||||
used to send data asynchronously back to the parent, without further need for
|
||||
the parent to poll for changes. This is useful for monitoring systems managing
|
||||
a large fleet of machines, or to alert the parent of unexpected state changes.
|
||||
|
||||
.. code-block:: python
|
||||
|
||||
def tail_log_file(channel, path='/var/log/messages'):
|
||||
"""
|
||||
Forward new lines in a log file to the parent.
|
||||
"""
|
||||
size = os.path.getsize(path)
|
||||
|
||||
while channel.open():
|
||||
new_size = os.path.getsize(path)
|
||||
if new_size == size:
|
||||
time.sleep(1)
|
||||
continue
|
||||
elif new_size < size:
|
||||
size = 0
|
||||
|
||||
fp = file(path, 'r')
|
||||
fp.seek(size)
|
||||
channel.send(fp.read(new_size - size))
|
||||
fp.close()
|
||||
size = new_size
|
||||
|
||||
|
||||
Compatibility
|
||||
#############
|
||||
|
||||
The package is written using syntax compatible all the way back to **Python
|
||||
2.4** released November 2004, making it suitable for managing a fleet of
|
||||
potentially ancient corporate hardware. For example econtext can be used out of
|
||||
the box against Red Hat Enterprise Linux 5, which was released in 2007.
|
||||
|
||||
Loading…
Reference in New Issue