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Package for extending the Calmjs framework to support the usage of webpack for the generation of deployable artifacts from JavaScript source code provided by Python packages in conjunction with standard JavaScript or Node.js packages sourced from npm or other similar package repositories.

Project description


Provide the integration of webpack into a Python environment through the Calmjs framework to facilitate the usage of JavaScript sources included with Python packages in conjunction with Node.js packages sourced from npm or similar package repositories, for the declaration and production of prebuilt JavaScript artifacts with webpack in a manner that allow reuse and extension by Python packages’ dependants.


Web applications may be created using any language as their backends, however interactive front-end user interfaces that they may provide ultimately rely on some form of JavaScript. This is especially true if associated functionalities are sourced from Node.js based package management systems such as npm. However, backend languages that offer their own package management system typically lack comprehensive integration with npm, or integration is tightly coupled with whatever framework that is not reusable in a more generalized manner.

A common way to address this issue is that a package may be forced to be split into two, or at the very least a completely separate deployment system is used, in order for the JavaScript tools to manage the front- end facing parts. On top of this, these separate systems do not necessarily communicate with each other. This results in issues such as difficulties in building the software stack, deployments being flaky and non-reproducible outside of the project’s context, limiting reusability of all the components at hand as the entire process is typically tightly coupled to the underlying source repository. Ultimately, this leaves the users of the backend language not able to convey front end deployment information across package boundaries for reuse by their dependents (e.g. for other downstream packages to extend the package in ways that promote reusability in a way that is well-tested.)

This kind of self-contained behavior also plagues webpack, where each Node.js package provide the resulting artifact, but not necessarily the methods that went into generating them in a form that is reusable. Sure, most typical use case for those packages can be addressed by simply specifying the entry point, however for systems that offer dynamic plugin-based systems this quickly becomes problematic, as webpack requires that all imports be known at build time. This makes arbitrary extensions very difficult to implement without a separate system that acts as an overseer for what modules names are available and where they might be.

As the goal of the Calmjs framework is to allow Python packages to expose their JavaScript code as if they are part of the npm managed module system from the client side code, this package, calmjs.webpack, leverages that capability to provide not only the standard invocation method for webpack for Python packages, but also the ability for downstream packages the option to generate comprehensive webpack artifacts or standalone webpack artifacts that only contain their specific extensions to be used in conjunction with other existing artifacts.


How calmjs.webpack works

The Calmjs framework provides the framework to allow Python packages to declare the dependencies they need against npm based packages for the JavaScript code they provide, and also enable Python packages to expose any JavaScript source files that they may contain in a declarative manner.

The utility included with calmjs.webpack provide the means to consume those declarations, treating the JavaScript files as both source and compilation target, with the final deployable artifact(s) being produced through webpack from the webpack package.

While the input source files made available through Python packages could be written in any format as understood by webpack, currently only standard ES5 is properly processed. The reason for this is that calmjs.parse, the parser library that calmjs.webpack make use for the parsing of JavaScript, currently only understand ES5, and is used for extracting all the import statements to create the dynamic Calmjs import system for webpack, and to also transpile the CommonJS and AMD (Asynchronous Module Definition) require statements to make use of this dynamic import system.

The resulting sources will be placed in a build directory, along with all the declared bundled sources acquired from the Node.js package managers or repositories, plus the (optionally) generated import module. A webpack configuration file will then be generated to include all the relevant sources as selected to enable the generation of the final artifact file. These can then be deployed to the appropriate environment, or the whole above process can be included as part of the functionality of the Python backend at hand through the API provided through this package.

Ultimately, the goal of calmjs.webpack is to ease the integration and interactions between of client-side JavaScript with server-side Python, by simplifying the task of building, shipping and deployment of the two set of sources in one shared package and environment. The Calmjs framework provides the linkage between these two environment and the tools provided by there will assist with the setup of a common, reproducible local Node.js environments.

Finally, for quality control, this package has integration with, which provides the tools needed to set up the test environment and harnesses for running of JavaScript tests that are part of the Python packages for the associated JavaScript code. However, that package is not declared as a direct dependency, as not all use cases will require the availability of that package. Please refer to installation section for details.


It is recommended that the local environment already have Node.js and npm installed at the very minimum to enable the installation of webpack, if it hasn’t already been installed and available. Also, the version of Python must be either 2.7 or 3.3+. Both PyPy and PyPy3 are supported, with the recommended versions being PyPy3-5.2 or greater, although PyPy3-2.4 should work, however there may be difficulties due to new versions of dependencies rejecting older versions of Python.

To install calmjs.webpack into a given Python environment, it may be installed directly from PyPI with the following command:

$ pip install calmjs.webpack

Installing/using webpack with calmjs

To establish a development/build environment for a Python package with the support for webpack through calmjs.webpack in the current working directory, the following command may be executed:

$ calmjs npm --install calmjs.webpack

While running npm install webpack (along with other related packages declared by calmjs.webpack that it needs from npm) will achieve the same effect, do note the Calmjs framework makes it possible for npm dependencies to be propagated down to dependent packages; such that if a Python package that have declared calmjs.webpack as a dependency (either through install_requires or an extras_require in its may have its complete set of dependencies on npm be installed using the following command (assuming the package is named example.package:

$ calmjs npm --install example.package

If the dependency on calmjs.webpack was declared as an extras_require dependency under a section named webpack, the command will then become the following:

$ calmjs npm --install example.package[webpack]

If the dependencies are declared correctly, using the above command will install all the required dependencies for the JavaScript/Node.js code required by example.package into the current directory through npm. Note that its dependents will also gain the declared dependencies.

For further details about how this all works can be found in the documentation for calmjs. Otherwise, please continue to the usage section.

Alternative installation methods (advanced users)

Development is still ongoing with calmjs.webpack, for the latest features and bug fixes, the development version can be installed through git like so:

$ pip install calmjs
$ pip install git+

Alternatively, the git repository can be cloned directly and execute python develop while inside the root of the source directory.

Keep in mind that calmjs MUST be available before the within the calmjs.webpack source tree is executed, for it needs the package_json writing capabilities in calmjs. Alternatively, please execute python egg_info if any message about Unknown distribution option: is noted during the invocation of

As calmjs is declared as both namespace and package, there are certain low-level setup that is required on the working Python environment to ensure that all modules within can be located correctly. However, versions of setuptools earlier than v31.0.0 does not create the required package namespace declarations when a package is installed using this development installation method when mixed with pip install within the same namespace. As a result, inconsistent import failures can happen for any modules under the calmjs namespace. As an example:

>>> import calmjs.webpack
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named 'calmjs.webpack'
>>> import calmjs.base
>>> import calmjs.webpack

If this behavior (and workaround) is undesirable, please ensure the installation of all calmjs related packages follow the same method (i.e. either python develop for all packages, or using the wheels acquired through pip), or upgrade setuptools to version 31 or greater and reinstall all affected packages.

Testing the installation

Finally, to verify for the successful installation of calmjs.webpack, the included tests may be executed through this command:

$ python -m unittest calmjs.webpack.tests.make_suite

However, if the steps to install external Node.js dependencies to the current directory was followed, the current directory may be specified as the CALMJS_TEST_ENV environment variable. Under POSIX compatible shells this may be executed instead from within that directory:

$ CALMJS_TEST_ENV=. python -m unittest calmjs.webpack.tests.make_suite

Do note that if the package is unavailable, a number of tests relating to integration with karma will be skipped. To avoid this, either install manually, or install calmjs.webpack using its extras dependencies declaration like so:

$ pip install calmjs.webpack[dev]


To generate a webpack artifact from packages that have JavaScript code exposed through the Calmjs module registry system that are already installed into the current environment, simply execute the following command:

$ calmjs webpack example.package

The following sections in this document will provide an overview on how to enable the JavaScript module export feature for a given Python package through the Calmjs module registry system, however a more thorough description on this topic may be found in the README provided by the calmjs package, under the section Export JavaScript code from Python packages.

Declaring JavaScript exports for the Python package

JavaScript code embedded within a Python package can be exposed to the Calmjs framework through the calmjs.module registry. For example, given the the following entry points for that registry defined by a package named example:

example = example

This is the most basic declaration that works for packages that share the same name as the import location provided.

The following is am example for packages that have nested submodules (called example.lib and

example.lib = example.lib =

While the import locations declared looks exactly like a Python module (as per the rules of a Python entry point), the calmjs.module registry will present them using the CommonJS/ES6 style import paths (i.e. 'example/lib' and 'example/app'). Thus users that wish to import those specific JavaScript modules will then require the required modules prefixed by those strings.

Please also note that the default source extractor will extract all JavaScript files within those directories. Finally, as a consequence of how the imports are done, it is recommended that no relative imports are to be used.

If the package at hand does not directly declare its dependency on calmjs, an explicit calmjs_module_registry=['calmjs.module'] may need to be declared in the setup function for the package to ensure that this default module registry will be used to acquire the JavaScript sources from.

Putting this together, the file should contain the following:

    # ... plus other declarations
    # this is recommended
        # plus other installation requirements
    # If the usage of the GPL is impossible for the project, or
    # declaring a direct dependency on calmjs packages is impossible
    # for the project for whatever other reasons (even though the
    # project itself will NOT be required to include/import ANY code
    # from the calmjs namespace), setup_requires may be used instead
    # of install_requires, and the following should also be included
    # as well:
        "devDependencies": {
            "webpack": "~2.6.0",
    # the entry points are required to allow calmjs to pick this up
    example = example
    example.lib = example.lib =

For the construction of the webpack artifact for the example package, it may be done like so through the calmjs webpack build tool, which would extract all the relevant sources, create a temporary build directory, generate the build manifest and invoke webpack on that file. An example run:

$ calmjs webpack example
Hash: 1dbcdb61e3afb4d2a383
Version: webpack 2.6.1
Time: 82ms
     Asset     Size  Chunks             Chunk Names
example.js  4.49 kB       0  [emitted]  main
   [1] /tmp/tmp7qvdjb5z/build/example/lib/core.js 51 bytes {0} [built]
       cjs require example/lib/core [2] /tmp/tmp7qvdjb5z/build/__calmjs_loader__.js 6:24-51
       cjs require example/lib/core [4] /tmp/tmp7qvdjb5z/build/example/app/index.js 1:10-37
   [2] /tmp/tmp7qvdjb5z/build/__calmjs_loader__.js 559 bytes {0} [built]
       cjs require __calmjs_loader__ [3] /tmp/tmp7qvdjb5z/build/__calmjs_bootstrap__.js 3:20-48
   [3] /tmp/tmp7qvdjb5z/build/__calmjs_bootstrap__.js 341 bytes {0} [built]
   [4] /tmp/tmp7qvdjb5z/build/example/app/index.js 74 bytes {0} [built]
       cjs require example/app/index [2] /tmp/tmp7qvdjb5z/build/__calmjs_loader__.js 7:25-53
    + 1 hidden modules

As the build process used by calmjs.webpack is executed in a separate build directory, all imports through the Node.js module system must be declared as extras_calmjs, as the availability of node_modules. will not be present. For instance, if example/app/index.js require the usage of the jquery and underscore modules like so:

var $ = require('jquery'),
    _ = require('underscore');

It will need to declare the target location sourced from npm plus the package_json for the dependencies, it will need to declare this in its

    # ...
        "dependencies": {
            "jquery": "~3.1.0",
            "underscore": "~1.8.0",
        "devDependencies": {
            # development dependencies from npm
    extras_calmjs = {
        'node_modules': {
            'jquery': 'jquery/dist/jquery.js',
            'underscore': 'underscore/underscore.js',

Once that is done, rerun python egg_info to write the freshly declared metadata into the package’s egg-info directory, so that it can be used from within the environment. calmjs npm --install example can now be invoked to install the npm dependencies into the current directory; to permit calmjs.webpack to find the required files sourced from npm to put into the build directory for webpack to locate them.

The resulting calmjs run may then end up looking something like this:

$ calmjs webpack example
Hash: fa76455e8abdb96273aa
Version: webpack 2.6.1
Time: 332ms
     Asset    Size  Chunks                    Chunk Names
example.js  326 kB       0  [emitted]  [big]  main
   [1] /tmp/tmposbsof05/build/example/lib/core.js 51 bytes {0} [built]
       cjs require example/lib/core [4] /tmp/tmposbsof05/build/__calmjs_loader__.js 7:24-51
       cjs require example/lib/core [6] /tmp/tmposbsof05/build/example/app/index.js 1:10-37
   [2] /tmp/tmposbsof05/build/jquery.js 268 kB {0} [built]
       cjs require jquery [4] /tmp/tmposbsof05/build/__calmjs_loader__.js 8:14-31
       cjs require jquery [6] /tmp/tmposbsof05/build/example/app/index.js 2:8-25
   [3] /tmp/tmposbsof05/build/underscore.js 52.9 kB {0} [built]
       cjs require underscore [4] /tmp/tmposbsof05/build/__calmjs_loader__.js 9:18-39
       cjs require underscore [6] /tmp/tmposbsof05/build/example/app/index.js 2:31-52
   [4] /tmp/tmposbsof05/build/__calmjs_loader__.js 633 bytes {0} [built]
       cjs require __calmjs_loader__ [5] /tmp/tmposbsof05/build/__calmjs_bootstrap__.js 3:20-48
   [5] /tmp/tmposbsof05/build/__calmjs_bootstrap__.js 341 bytes {0} [built]
   [6] /tmp/tmposbsof05/build/example/app/index.js 128 bytes {0} [built]
       cjs require example/app/index [4] /tmp/tmposbsof05/build/__calmjs_loader__.js 6:25-53
    + 1 hidden modules

Trigger test execution as part of webpack artifact building process

For testing, declare the appropriate entries to the module test registry that accompanies the module registry for the given package, and with the use of the karma runtime provided by the package, the tests may be executed as part of the webpack artifact build process. The command is simply this:

$ calmjs karma webpack example

Do note that both the devDependencies provided by both and calmjs.webpack must be installed. This can easily be done by declaring the appropriate install_requires, or manually install and then install the dependencies from npm using calmjs npm -D --install calmjs.webpack[dev].

Dynamic module imports

While webpack does natively support this to some extent, the support is only implemented through direct filesystem level support. In the case of Calmjs, where the imports are done using identifiers on the aliases explicitly defined in generated webpack.conf.js configuration, webpack is unable to resolve those aliases by default.

Instead of trying to make ContextReplacementPlugin work or writing another webpack plugin, a surrogate __calmjs__ import module is automatically generated and included in each generated artifact such that the dynamic imports will function as intended. The rationale for using this as a workaround is simply a desire to avoid possible API changes to webpack as plugins of these nature will end up being tightly coupled to webpack.

With the usage of a surrogate import module, the dynamic imports also work across multiple webpack artifacts generated through calmjs webpack, however this is an advanced topic thus further documentation will be required, as specific declaration/import order and various other caveats exists that complicates real world usage (e.g. correct handling of circular imports will always remain a non-trivial problem).

For the simple case, imagine the following JavaScript code:

var loader = function(module_name) {
    // the dynamic import
    var module = require(module_name);
    console.log(module + ' was loaded dynamically.');

var demo = loader('example/lib/core');

If the example/lib/core.js source file was exported by example package and was included in the webpack, the above dynamic import should function without issues at all by default without further configuration.

If this dynamic import module functionality is unwanted and that no dynamic imports are used by any JavaScript code to be included, this feature may be disabled by the --disable-calmjs-compat flag.

Handling of Webpack loaders

If a provided JavaScript module imports a target using the inline loader syntax, the default registry calmjs.webpack.loaderplugins will resolve a generic handler to copy the target files. This generic handler supports the chaining of loaders. If this behavior is unwanted, a static registry is defined at calmjs.webpack.static.loaderplugins for this purpose. If a mix of the two is needed (e.g. where some specific loader require special handling), it is also possible to register the specific handler to override the generic handler for that specific loader.

So if some JavaScript code contain a require statement like:

var readme = require('text!readme.txt');

And there exists a custom Calmjs module registry that provide those sources, the default loaderplugin handler registry will provide a standard handler that will process this, provided the loader package is available along with webpack on the working Node.js environment.

Testing standalone, finalized webpack artifacts

Webpack artifacts generated using the standard calmjs webpack toolchain runtime may be tested using the calmjs karma runtime provided by the package. Given a finalized example.webpack.js that implements the features provided by the example package, the artifact may be tested with the tests provided by the example package using the following command:

$ calmjs karma run \
    -t calmjs.webpack \
    --artifact=example.webpack.js \

The above command invokes the standalone Karma runner using the calmjs.webpack settings to test against the example.webpack.js artifact file, using the tests provided by the example package. The test execution is similar to the one during the development process.

Declaring prebuilt webpack artifacts for Python packages

Finally, to complete the Python package deployment story, the process should include the automatic generation and inclusion of the JavaScript artifacts in the resulting Python wheel. This can be achieved by specifying an entry in the calmjs.artifacts registry, with the key being the filename of the artifact and the value being the import location to a builder. A default builder function provided at calmjs.webpack.artifact:complete_webpack will enable the generation of a complete webpack artifact for the Python package. The builder calmjs.webpack.artifact:optimize_webpack will do the same, but with the optimize options enabled (currently only the minimize output is supported).

For example, a configuration that contains both forms might look like so:

example.webpack.js = calmjs.webpack.artifact:complete_webpack
example.webpack.min.js = calmjs.webpack.artifact:optimize_webpack

Once those entry points are added to and the package metadata is regenerated using egg_info, running calmjs artifact build example.package will make use of the webpack toolchain and build the artifact at example.webpack.js inside the calmjs_artifacts directory within the package metadata directory for example.package. Alternatively, for solution more integrated with setuptools, the setup function in should also enable the build_calmjs_artifacts flag such that build will also trigger the building process. This is useful for automatically generating and including the artifact as part of the wheel building process. Consider this

    # ... other required fields truncated
    # ... other entry points truncated
    example.package = example.package

    example.webpack.js = calmjs.webpack.artifact:complete_webpack
    example.webpack.min.js = calmjs.webpack.artifact:optimize_webpack

Building the wheel using may result in something like this. Note that the execution of webpack was part of the process and that the metadata (egg-info) directory was then built into the wheel.

$ python bdist_wheel
running bdist_wheel
running build
running build_calmjs_artifacts
automatically picked registries ['calmjs.module'] for sourcepaths
using loaderplugin registry 'calmjs.webpack.loaderplugins'
using calmjs bootstrap; webpack.output.library set to '__calmjs__'
Version: webpack 2.6.1
Time: 240ms
             Asset    Size  Chunks                    Chunk Names
example.webpack.js   10 kB       0  [emitted]  [big]  main
running install_egg_info
Copying src/example.package.egg-info to build/.../wheel/example.package...
running install_scripts
creating build/.../wheel/example.package-1.0.dist-info/WHEEL

For testing the package artifact, the following entry point should also be specified under the calmjs.artifacts.tests registry, such that running calmjs artifact karma example.package will execute the JavaScript tests declared by example.package against the artifacts that were declared in calmjs.artifacts.

example.webpack.js = calmjs.webpack.artifact:test_complete_webpack
example.webpack.min.js = calmjs.webpack.artifact:test_complete_webpack

Note that the same test_complete_webpack test builder will be able to test the optimize_webpack artifact also.


The following are some known issues with regards to this package and its integration with other Python/Node.js packages.

CRITICAL calmjs.runtime WebpackRuntimeError: unable to locate ‘webpack’

This means the current Node.js environment is missing the webpack package from npm; either install it manually with it or through calmjs on this package. If a given Python package is required to use webpack to generate the package, its package_json should declare that, or declare dependency on calmjs.webpack.

CRITICAL calmjs.runtime WebpackExitError: webpack terminated

This can be caused by a variety of reasons; it can be due to invalid syntax in the provided JavaScript code, or that the configuration not containing enough information for webpack to correctly execute, or that specific calmjs webpack flags have been enabled in a way that is incompatible with webpack. To extract further information about the error, the same calmjs command may be executed once more with the --verbose and/or --debug flag enabled for extra log message which may reveal further information about the nature of the error, or that the full traceback may provide further information. Detailed information must be included for the filing of bug reports on the issue tracker.

UserWarning: Unknown distribution option:

During setup and installation using the development method, if this warning message is shown, please ensure the egg metadata is correctly generated by running python egg_info in the source directory, as the package calmjs was not available when the setup script was initially executed.

WARNING could not locate ‘package.json’ for the npm package ‘???-loader’

The warning message is triggered when there was an attempt to use a webpack loader without the appropriate loader module installed into the working Node.js environment. As a quick workaround to the webpack artifact build issue, the missing package installation command may be attempted, however the correct solution is for that package to declare the correct loader package as the dependency in package_json.


1.0.2 (2018-05-24)

  • Provide a builder that will generate an artifact with the supported optimize flags enabled. [ #3 ]

1.0.1 (2018-05-03)

  • Update the export_target production and usage of working_dir to be inline with what is expected by calmjs-3.1.0. [ #2 ]

1.0.0 (2018-01-12)

  • Initial implementation of the Calmjs integration tool that enable the production of webpack artifacts from JavaScript sources that are included with Python packages, that also allow import of their dependencies sourced through npm through the Calmjs framework.
  • Enabled the calmjs webpack tool entry point.
  • Also provide integration with by correcting the correct hooks so that this package can be used as an advice package for the execution of tests against artifacts generated through this package, through the usage of calmjs karma webpack.
  • Support for prebuilt artifacts for packages is provided through calmjs.artifacts registry; default complete builders for both building and testing are available via the calmjs.webpack.artifact module.
  • Webpack is pinned to ~2.6.0, as that is the current stable version that is verified to work with building and testing of artifacts.

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