A tree-shaking tool for Python.
A tree-shaking tool for Python.
What it does
If you give treeshaker a root environment (specified by a
file), a list of target packages
target_packages (in this case
otherpkg), and a target module (in this case
mypkg.target), treeshaker will
create an output directory that contains
- the subset of modules among all the modules in all the
target_packagesthat are needed to import the target module, copied as .py files directly into the root of the output directory and
- a new
requirements.txtfile containing the subset of the root
requirements.txtlines needed to import all the modules in (1)
An end user can then open the folder,
pip install -r requirements.txt, and
import the target module, without installing or obtaining the complete code for
any of the
$ pip install treeshaker
Define your root environment in a
requirements.txtfile and ensure the listed packages are available in your current Python environment. If you don't have a
requirements.txtfile yet, you can run
$ pip install <package that provides target module> $ pip freeze > requirements.txt
If you already have a
requirements.txtfile, you can instead run
$ pip install -r requirements.txt
Create a configuration file (see the example config file for reference), specifying the location of your root
requirements.txtfile as well as the details of what targets should be built and how.
git clone https://github.com/sclabs/treeshaker.git
pip install . ./examples/mypkg ./examples/otherpkg ./examples/externaldep ./examples/otherdep
treeshaker --config examples/treeshaker.cfg
To clean up after the demo run
$ python examples/clean.py
Building multiple targets versus building one target
To build one specific target, run
$ treeshaker --target <target_module_name>
treeshaker will find the configuration file section
(which must exist) to determine the
outdir (a required key in every
[target:<target_module>] section) and all other parameters for the build.
To build a list of targets, add the desired targets to the
(as keys with no values) and run
The copied modules will be renamed if necessary to avoid name conflicts.
If one copied module is
mypkg.dep and another is
otherpkg.dep, these will be
During module renaming, treeshaker will attempt to rewrite import statements in the copied modules as necessary. The logic for doing this is quite rudimentary and is only expected to succeed when the import is of the form
from mypkg.mymod import not_a_module
In these cases, when
mypkg.mymod is copied, it will be renamed and a simple
find-and-replace will "fix" the import statement.
The following form of import is expected to fail:
from mypkg import mymod
Relative imports are generally also expected to fail, though they may work when importing a sibling module whose name has no conflicts.
Configuration file inheritance
If a key is missing from a
[target:<target_module>] section, treeshaker will
fall back to looking for the key in the
The example configuration file defines many keys in
[target] section, but all of these can be overridden on a per-target basis
by adding the key to the corresponding
You can use the special string
<outdir> in the
[target] section or any
[target:<target_module>] section and it will be replaced with the actual
outdir at runtime.
Functions and/or classes listed in a
functions key and python-fire
components listed in a
fire_components key in the configuration file will be
<outdir>/README.md, using their docstring or fire help page,
You can also manually write a README section that will be included in
<outdir>/README.md by specifying a filename in a
readme key. If this file
does not exist on the disk, it will not be included.
Custom configuration file name
To run treeshaker using a specific configuration file, run
$ treeshaker --config path/to/customconfig.cfg
How does it work?
Dependency graph construction
Python provides modulefinder in the
standard library, but it is not quite powerful of flexible enough to accomplish
what we want. Instead, we use the modulegraph
library, which is both performant (thanks to the useful
excludes argument) and
flexible (it creates a dependency graph that we can analyze in detail to
classify imported modules).
Matching PyPI package names to root module names
How can treeshaker determine that if you import a module from
requirements.txt line is e.g.,
pipreqs has compiled a mapping of PyPI names to root module names for many PyPI packages; we use this list to perform this matching. We considered adding a dependency on pipreqs, but we decided to vendor it ourselves to avoid an additional seven dependent package installs (we only use the single file that contains the mapping).
For consistency, we choose to use the actual module name (the one used in
imports and the one that reflects the location of the package on-disk after
install) to specify the
While treeshaking is a cool concept, there's rarely any real need to perform treeshaking on Python code. This library was created for a highly specific use case: automatically minimizing the amount of code revealed from a monolithic private codebase when providing code for one specific module (or more specifically, the task that module performs).
In a monolithic library design, it's possible to have a very large number of modules and a large number of tasks that the library can accomplish. It might be better to apply the "single responsibility principle" and design a set of libraries that each do one task, but what happens when the monolith already exists and a redesign is not feasible? In most situations, there is no harm in distributing the entire library even if the person requesting the code wants to accomplish just one task. However, when the library code is private, it may be desirable to minimize the total amount of code "exposed" or "revealed" to the requestor.
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