require() for Python

This Python module provides a new approach to loading Python modules similar to Node's require() that is decoupled from the Python import mechanism.

import require
status = require('./lib/status')
status.yell()

This is particularly useful in Python applications with a plugin architecture and solves potential problems when using traditional Python modules that can easily result in dependency conflicts.

Installation

pip install py-require

Known Issues

• In Python 2, no statement must be on the first line of the file. This is due to the fact that require prepends the text from __future__ import absolute_import; in the first first line to avoid RuntimeWarnings when import other modules using Pythons standard import mechanism.

API

require.new(path=(), write_bytecode=None)

Create a new independent instance. Note that the path argument is processed with require.preprocess_path().

require(file, directory=None, path=(), reload=False, cascade=False, inplace=False, get_exports=True)

Loads a Python module by filename. If file is a relative path starting with ./, it will be loaded relative to directory. Otherwise, if it is not an absolute path, it will be searched in the search path. Note that file should be a UNIX-style path on every platform.

The algorithm will check the following forms of file:

• <file>
• <file>c@x-y
• <file>/__init__.py
• <file>/__init__.pyc@x-y
• <file>.py
• <file>.pyc@x-y

c@x-y is the suffix of bytecode files for the current Python version. If file is the string '.', it will be translated to './__init__.py'.

Parameters

• file -- The name of the Python module to load.
  
• directory -- The directory to load a local module from. If omitted, will be determined automatically from the caller's global scope using sys._getframe().
  
• path -- A list of additional search paths when loading other modules with require(). Subsequent loads inherit this search path. Note that these paths are preprocesed with require.preprocess_path(), thus elements that start with ! (exclamation mark) will be assumed relative to the directory that the require() function is called from.
• reload -- True to force reload the module.
  
• cascade -- If reload is True, passing True causes a cascade reload.
  
• inplace -- If reload is True, modules will be reloaded in-place instead of creating a new module object.
• get_exports -- Return the exports member of the module if there is any. False can be passed to always get the actual module object. Can also be callable that is passed the module object. The result of this callable is returned.

Return

A types.ModuleType object, unless the module has a member called exports, in which case the value of this member will be returned.

Raises

require.error -- If the module could not be found or loaded.

require.load_file(load_file, real_file=None, info=None, path=(), reload=False, cascade=False, inplace=False, get_exports=True, cascade_index=None, parent_context=None)

Load a Python module by filename. If real_file is specified, it must be the name of the original source file and is the name under which the module is stored. load_file must be the name of a bytecache file in that case.

The info parameter is passed to Require.init_module() and Require.free_module() and must be the same as would be returned by Require.find_module().

require.Require(path=(), write_bytecode=None)

Class of the require module that can be instantiated to create a new, decoupled require environment. You can also subclass it and overwrite the Require.find_module() method.

import require
require = require.Require()
require('./hello').say_hello()

require.path

A list of global search directories that will always be taken into account when using require().

require.modules

This dictionary maps absolute filenames to the Python modules that are loaded by require().

Changelog

v0.17

• fix loading the require module without the import statement when another instance of the require module was already imported and present in sys.modules

v0.16

• require.path is now taken into account when searching for modules again
• add require.new() method
• add require.preprocess_path() method
• add Require(_stackdepth=0) argument
• require.new(path) and require(path) arguments are now preprocessed with the require.preprocess_path() method

v0.15

• add require.load_file() function
• add Require.init_module() function
• add Require.free_module() function
• filenames are now normalized before using them as module names
• Require.find_module() must now return a three-element tuple (load_file, real_file, info) instead of a two element tuple

v0.14

• removed require.new()
• add Require(write_bytecode) argument
• add RequireModuleContext.path_all property
• replace Require._get_best_candidate() with Require.find_module()

v0.13

• fix NameError where old bcsuffix variable was used instead of Require.bytecache_suffix

v0.12

• add global require member to require.py for cases when sys.modules can not be patched
• prevent sys.modules being patched when there is already a module named require that is not the same object as the currently executed require module

v0.11

• rewrite, using Require class and cleaner code base
• add require.new() (#11)
• support for translating '.' to './__init__.py' (#10)
• fix bug with parent context not being inherited when calling the require module directly instead of using require.require(), by introducing a new _stackdepth parameter

v0.10

• fix #9 – require module is now a custom types.ModuleType instance that implements __call__()

v0.9

• add require(get_exports) parameter

v0.8

• removed '.' path from default value of require.path

v0.7

• rename module to require from shroud
• sys.module hook to allow calling require as a module instead of having to use from require import require
• directory to load local modules from (./) now falls back to the current working directory

License

The MIT License (MIT)

Copyright (c) 2016 Niklas Rosenstein

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.