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A Python framework for building toolchains and utilities for working with the Node.js ecosystem from within a Python environment.

Project Description


A Python framework for building toolchains and utilities for working with the Node.js ecosystem from within a Python environment.


Calmjs defines an extensible framework for interoperability between Python and Node.js runtime for Python packages, so they can interoperate with all aspects of Node.js/JavaScript development ecosystems. The goal of the Calmjs framework is to aid the development, testing, and deployment of Python packages that also include JavaScript.


First, this is achieved by providing Python packages the ability to declare dependencies on Node.js/JavaScript packages or source files that are required to complete their functionality. This common framework will ensure the accessibility of these metadata under a common protocol, to avoid incompatible declarations that are not portable between different projects and environments, or being otherwise scattered across different tools or locations or be duplicated within the same working environments by different sets of tools that are unable to communicate states between each other, which are common sources of errors and hardships for building and deployment.

Second, by offering a set of tools built on top of this extensible framework to work with these declarations for generating the configuration files for required Node.js tools, so that they can construct the required the build and/or runtime environment for their functionality.

Ultimately, this permits better Node.js integration with a given Python environment, lowering the amount of effort needed to achieve continuous integration and/or delivery of Python packages in conjunction with Node.js/JavaScript packages in a reproducible manner.


In order to achieve this, the Calmjs framework provides a set of extension to setuptools that assists with the tracking and management of dependencies of JavaScript or Node.js based packages (such as ones through npm) for a given Python package. It also provides a number of base classes that can be used to build custom toolchains that implement different strategies for managing and compiling required JavaScript code and related assets into the deployment artifacts that an application server may use, or to generate test harnesses to ensure correctness under both the development and production environment. These extra functionalities will be provided by other Python packages under the calmjs namespace in order to realize this modular architecture.

The name Calmjs was originally derived from the steps in the first iteration of the toolchain which involves the steps compile, assemble, and linkage into a module of JavaScript using the namespace from the host Python package. The m in the logo is the ear of a rabbit. The reason this animal is chosen as the mascot for this project is because of their dietary habits, as it’s analogous to how JavaScript code is typically turned into a minimally usable level by other tools and framework.


A framework for integration with Node.js based package managers

Through setuptools command hooks, calmjs provides Python packages with the ability to declare and manage manifest definition files for Node.js based package management systems (e.g. such as package.json for npm). Under typical usage, this means the declaration of dependencies or devDependencies for the JavaScript packages needed by a given Python package can be tracked, all within the setuptools framework through the extensions provided by calmjs.

The other part of this infrastructure is that these declarations follow the Python package dependency graph. Developers and users can make use of the calmjs console command entry point, or through setuptools, to generate a manifest file to facilitate the installation of Node.js packages required by the Python packages within the completed application stack, tailored for all the packages at hand.

calmjs includes the support for npm by default.

Export JavaScript code out of Python packages with the same namespace

A given Python package that included associated JavaScript source code within the same Python module and namespace structure alongside Python source code within the source tree, will be able to declare those namespaces as the root for those JavaScript modules under the exact same Python package namespace through setuptools entry points.

These declarations will be available through registries exposed by the calmjs module registry system for other packages to turn those declarations through the API provided by the framework into working JavaScript code following the same declared module and namespace structures. The default module registry will make use of the / character (instead of the . character like in Python) as the separator for the names due to established naming conventions in JavaScript (and in ES6 towards the future).

Other tools that works with the Calmjs framework can then make use of these raw JavaScript source files, turning them into actual usable Node.js modules for local consumption, or AMD (Asynchronous Module Definition) artifacts for consumption over the web. This leads to…

Better integration of JavaScript toolchains into Python environments

This is achieved by providing a framework for building toolchains for working with tools written in JavaScript for Node.js/JavaScript environments that integrates properly with existing Python packages and environments.

There are no limitations as to how or what can be done with the tools or the source files, as this is left as an implementation detail. For an example please refer to the calmjs.rjs Python package, which allows the production of AMD artifacts from JavaScript packages embedded inside Python packages.

Generally, toolchains can be built to find and load all Python packages (through the calmjs registry system) that have any JavaScript source files, and those will be extracted, go through the appropriate transpilers (if any) in order to build deployable artifacts. Test harnesses can be set up to aid with running of unit tests, functional testing and naturally the final integration tests needed for a successful deployment.

Well-defined modular architecture to ensure code reuse and extensibility

The features described so far are built upon a foundation of generic classes and modules, so that the support for additional JavaScript tools or custom process for handling transpilation can be as simple as creating a new module for a couple of classes with additional parameters with the relevant setuptools entry points.

In fact, calmjs out of the box only ships with just the core framework plus the npm interfacing part, with the support for tools like Bower or r.js as completely separate packages (as calmjs.bower and calmjs.rjs respectively), such that projects, environments or sites that do not need the functionality those packages provide can simply opt to not have them installed.


As the goal of calmjs is to integrate Node.js and npm into a Python environment, they need to be available within the environment; if they are not installed please follow the installation steps for Node.js appropriate for the target operating system/environment/platform.

To install calmjs into a given Python environment, the following command can be executed to install directly from PyPI:

$ pip install calmjs

Alternative installation methods (for developers, advanced users)

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

$ pip install git+

Alternatively, the git repository can be cloned directly and execute python develop while inside the root of the source directory. However this method WILL require all packages under the calmjs namespace to be uninstalled and be reinstalled using this development only method.

As calmjs is declared as both a namespace and a package, mixing installation methods as described above when installing with other calmjs packages may result in the module importer being unable to look up the target files. If such an error does arise please remove all modules and only stick with a single installation method for all packages within the calmjs namespace.

Testing the installation

To ensure that the calmjs installation is functioning correctly, the built-in testsuite can be executed by the following:

$ python -m unittest calmjs.tests.make_suite

If there are failures, please file an issue on the issue tracker with the full traceback, and/or the method of installation. Please also remember to include platform specific information, such as Python version, operating system environments and version, and other related information related to the issue at hand.


When installed to a particular Python environment, the calmjs command-line utility will become available within there.

$ calmjs
usage: calmjs [-h] [-d] [-q] [-v] [-V] <command> ...

positional arguments:
    npm          npm support for the calmjs framework

optional arguments:
  -h, --help     show this help message and exit

As mentioned, npm support is built-in so it is always available; to access its help, simply execute calmjs npm -h, which will then list the options available for that particular subcommand. If other subcommands are available (which will be provided by other calmjs integration packages) they will be listed as a <command> and their specific help messages will be accessible in the same manner.

Declare and use a package.json for a given Python package

If a package wish to declare dependencies on packages hosted by npm, it may do something like this in its

from setuptools import setup

package_json = {
    "dependencies": {
        "jquery": "~3.0.0",
        "underscore": "~1.8.0",


Running python install in the directory the resides in will write that package_json fragment into the package’s egg-info metadata section, provided that it is a valid JSON string or a dictionary without incompatible data types.

All packages that ultimately depending on this example.package will have the option to inherit this package.json egg-info metadata. One way to do this is through that package’s By invoking npm --init from there, a new package.json will be written to the current directory as if running npm init with all the dependencies declared through the Python package dependency tree for the given Python package.

Alternatively, call calmjs npm --init example.package will do the same thing, provided that the example.package is available through the current Python environment’s import system.

Dealing with npm dependencies with Python package dependencies

Remember, flat is better than nested. So all dependencies (and devDependencies) declared by any upstream Python package will be automatically inherited by all its downstream packages, but they have the option to override it with whatever they want through the mechanism as described above. They can set a JavaScript or Node.js package to whatever versions desired, or even simply remove that dependency completely by setting the version to None.

Through this inheritance mechanism whenever an actual package.json is needed, the dependencies are flattened for consumption by the respective JavaScript package managers, or by the desired toolchain to make use of the declared information to generate the desired artifacts to achieve whatever desired task at hand.

Of course, if the nested style of packages and dependency in the same style as npm is desired, no one is forced to use this, they are free to split their packages up to Python and JavaScript bits and have them be deployed and hosted on both PyPI (for pip) and npm respectively and then figure out how to bring them back together in a coherent manner. Don’t ask (or debate with) the author on how the latter option is better or easier for everyone (developers, system integrators and end-users) involved.

Declare explicit dependencies on paths inside node_modules

Given that the dependencies on specific versions of packages sourced from npm is explicitly specified, build tools will benefit again from explicit declarations on files needed from those packages. Namely, the compiled packages could be declared in the extras_calmjs section in JSON string much like package_json, like so:

extras_calmjs = {
    'node_modules': {
        'jquery': 'jquery/dist/jquery.js',
        'underscore': 'underscore/underscore.js',


Since node_modules is declared to be an extras_key, conflicting declarations between packages within the environment will be resolved and merged in the same manner as dependencies conflicts declared in package_json.

Please do note that complete path names must be declared (note that the .js filename suffix is included in the example); directories can also be declared. However, as these declarations are done from within Python, explicit, full paths are required thus it is up to downstream integration packages to properly handle and/or convert this into the conventions that standard Node.js tools might expect (i.e. where the .js filename suffix is omitted).

Export JavaScript code from Python packages

Furthering the previous example, if the files and directories inside example.package are laid out like so:

├── example
│   ├──
│   └── package
│       ├──
│       ├──
│       ├──
│       ├── ui.js
│       ├──
│       └── widget.js

To declare the JavaScript source files within ./example/package as JavaScript modules through calmjs, an entry point can be declared like so in the file:

    example.package = example.package

The default method will expose the two source files with the following names:

- 'example/package/ui'
- 'example/package/widget'

For some projects, it may be undesirable to permit this automated method to extract all the available JavaScript source files from within the given Python module.

To get around this, it is possible to declare new module registries through the Calmjs framework. Provided that the ModuleRegistry subclass was set up correctly to generate the desired modules from a given package, simply declare this as a calmjs.registry entry point like so:

    example.module = example.package.registry:ExampleModuleRegistry

Do note that while the names permitted for an entry point name is quite unrestricted, these registry names should be of a standard dotted namespace format to ensure maximum tool compatibility, as these can be specified from the command line through tools that utilizes this system.

Once the registry was declared, simply replace calmjs.module with the name of that, along with a calmjs_module_registry attribute that declare this example.module registry is the default registry to use with this package.

    example.package = example.package

Within the Calmjs framework, tools can be explicitly specified to capture modules from any or all module registries registered to the framework. One other registry was also defined. If the entry point was declared like so:

    example.package = example.package

The separator for the namespace and the module will use the . character instead of /. However given that the . character is a valid name for a JavaScript module, the usage of this may create issues with certain JavaScript tools. However, AMD based module systems can generally deal with . without issues so using those may end up resulting in somewhat more Python-like feel when dealing with imports while using JavaScript, though at a slight cost of whatever standards compliance with it.

By default, another registry with the .tests suffix is also declared as a compliment to the previously introduced registries, which packages can make use of to declare JavaScript test code that accompanies the respective modules that have been declared. For example:

    example.package = example.package

    example.package = example.package.tests

Much like the first example, this declares example.package as a Python namespace module that exports JavaScript code, with the declaration following that declaring the module that contains the tests that accompanies that.

Integration with npm through calmjs npm

As mentioned, it is possible to make use of the package.json generation capabilities from outside of setuptools. Users can easily do the same through the built-in calmjs npm tool:

usage: calmjs npm [-h] [-d] [-q] [-v] [-V] [--view] [--init]
                  [--install] [-i] [-m] [-w] [-E]
                  package_names [package_names ...]

positional arguments:
  package_names      names of the python package to use

optional arguments:
  -h, --help         show this help message and exit
  -i, --interactive  enable interactive prompt; if an action
                     requires an explicit response but none were
                     specified through flags (i.e. overwrite),
                     prompt for response; disabled by default
  -m, --merge        merge generated 'package.json' with the one in
                     current directory; if interactive mode is not
                     enabled, implies overwrite, else the difference
                     will be displayed
  -w, --overwrite    automatically overwrite any file changes to
                     current directory without prompting
  -E, --explicit     explicit mode disables resolution for
                     dependencies; only the specified Python
                     package(s) will be used.

Naturally, the same --init functionality shown above with the setuptools framework is available, however package names can be supplied for generating the target package.json file from anywhere on the filesystem, provided that the Python environment has all the required packages installed. For instance, if the Node.js packages for example.package is to be installed, this can be invoked to view the package.json that would be generated:

$ calmjs -v npm --view example.package
2016-09-01 16:37:18,398 INFO calmjs.cli generating a flattened
'package.json' for 'example.package'
    "dependencies": {
        "jquery": "~3.0.0",
        "underscore": "~1.8.0",
    "devDependencies": {},
    "name": "example.package"


Documentation on how to extend the Toolchain class to support use cases is currently incomplete. This is usually combined together with a calmjs.runtime.DriverRuntime to hook into the calmjs runtime.

Unfortunately at this time a detailed guide on how to do this is not yet written, however working extensions have been created - for a working example on how this may be achieved please refer to calmjs.rjs.


The following may be some issues that may be encountered with typical usage of calmjs.

CRITICAL calmjs.runtime terminating due to a critical error

If calmjs encounters any unexpected situation, it may abort like so:

$ calmjs npm --install
CRITICAL calmjs.runtime terminating due to a critical error

If no useful ERROR message is listed before, please try running again using a debug flag (either -d or --debug).

$ calmjs -d npm --install
CRITICAL calmjs.runtime terminating due to exception
Traceback (most recent call last):

Specifying the debug flag twice will enable the post_mortem mode, where a debugger will be fired at the point of failure. Authors of runtime modules may find this useful during their development cycles. Do note that the default debugger is set up to only be triggered only on this termination; if errors and/or exceptions occur during the setup stage of the calmjs runtime, the errors will only simply be logged.

ERROR bad ‘calmjs.runtime’ entry point

This is typically caused by improper removal of locally installed packages that had an entry point registered, an addon package to calmjs registered entry points pointing to bad import locations, or conflicting installation methods was used for the current environment as outlined in the installation section of this document. Either reinstall the broken package again with the correct installation method for the environment, or fully uninstall or remove files belonging to the packages or sources that are triggering the undesirable error messages.
bad entry point
This is caused by packages defining malformed entry point. The name of the package triggering this error will be noted in the log; the error may be reported to its developer.

Environmental variables being ignored/not passed to underlying tools

Generally speaking, the Calmjs framework filters out all environmental variables except for the bare minimum by default, and only passes a limited number to the underlying tool. These are the PATH and the NODE_PATH variables, plus platform specific variables to enable execution of scripts and binaries.

Runtime reporting ‘unrecognized arguments:’ on recognized ones

For instance, if the calmjs binary was executed like so resulting in error message may look like this:

$ calmjs subcmd1 subcmd2 --flag item
usage: calmjs subcmd1 ... [--flag FLAG]
calmjs subcmd1: error: unrecognized arguments: --flag

This means that --flag is unrecognized by the second subcommand (i.e. the calmjs subcmd1 subcmd2 command) as that was placed after subcmd2, but the subparser for subcmd1 flagged that as an error. Unfortunately there are a number of issues in the argparse module that makes it difficult to resolve this problem, so for the mean time please ensure the flag is provided at the correct subcommand level (i.e. in this case, calmjs subcmd1 --flag item subcmd2), otherwise consult the help at the correct level by appending -h to each of the valid subcommands.

Module registry not locating files from namespace packages

There are a number of edge cases associated with namespace packages in Python, especially if they are provided on the system through different methods (i.e. mix of zipped eggs, wheels and development packages). While workarounds for handling of namespace modules for the given packages are provided, there are limitations in place. One such cause is due to complexity in dealing with zipped eggs; if this is an issue, please ensure that the affected package has zip_safe declared as false, or alternatively generate a Python wheel then install that wheel, if the target Python environment has that as the standard installation format.


2.1.0 (2016-11-29)

  • Namespace packages that have a module explicitly provided should still be able to be looked up if a valid entry point is provided; naturally if the module isn’t declared correctly then the behavior remains unchanged (github issue #5)
  • Name field in package.json should contain project names standard to Node.js, i.e. if extras are specified, it should be stripped. This is done so that that npm will not choke on it with a warning and die. (github issue #4)

2.0.0 (2016-11-16)

  • Expose the indexer module functions mapper and modgen as public.
  • Completely refactored the Toolchain class to have much more consistent method naming convention and argument lists.
  • The compile method now reads from an instance specific list of methods which allow very customizable compilation steps.
  • Specific ways for a toolchain to skip specific names based.
  • Fixed copying of bundle sources to targets nested in subdirectories.
  • The Spec callback system is now renamed to advice system and more comprehensively implemented; every step within the toolchain will execute advices before and after for each respective step that have been registered under the matching identifiers. The identifiers for advices are are formalized as constants that can be imported from the calmjs.toolchain module.
  • The advice system has dedicated exceptions which can be raised to signal an abort or cleanly stop a run.
  • A couple spec keys were formalized, which are BUILD_DIR and CONFIG_JS_FILES, reserved for the build directory and marking out configuration JavaScript files.
  • On a successful toolchain call, all advices registered to the spec under the key calmjs.toolchain.SUCCESS will now be invoked.
  • Dedicated runtime provided for Toolchain subclasses, joining the ranks of a few other BaseDriver subclasses. This is implemented as calmjs.runtime.ToolchainRuntime.
  • calmjs.runtime.Runtime can be subclassed and nested as it will now nest all BaseRuntime. Also the init method is removed, just use __init__ and standard subclassing super usage rules.
  • The default ArgumentParser instance for every Runtime will no longer be created until accessed, as it is now a property.
  • Provide a way for packages to declare the primary module registry or registries it declared packages for through a new setup keyword calmjs_module_registry, if required and desired.
  • The default set of module registry names have been changed. Registry calmjs.pythonic is renamed to; the related testing related registry is renamed to include the full name of its implied target.
  • Reserved a small set of core (already defined) registries for the calmjs framework, which is formally defined and enforce by the registry itself.
  • Corrected interactive-mode detection.
  • Helpers for source map generation for simple transpilation.

1.0.3 (2016-09-07)

  • Fixed the issue with bad environmental variables for subprocess.Popen for Windows under Python 2.7.
  • Other minor testing fixes on CI platforms.

1.0.2 (2016-09-04)

  • Fixed invocation of binaries on the Windows platform.
  • Corrected some minor wording.

1.0.0 (2016-09-02)

  • Initial release of the calmjs framework foundation.
  • A cli runtime entry point is provided, named calmjs.
  • Provide core integration with npm and generation of package.json through the setuptools framework; this is accessible as a setuptool command or through calmjs runtime.
  • Provide a registry framework for use within calmjs.
  • Provide core registries for registering packages for use by calmjs through the predefined setuptools entry points and groups.
  • Provide a cli tool driver framework for interacting with node and other Node.js based or other command line tools.
  • Provide the base toolchain framework, built on top of the tool driver framework.
  • Provide modules for doing integration testing for modules that build on top of the calmjs framework.
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