functools32 dependency in installBuildRequirements

While trying to upgrade my PyGradle project to python3, I see that the build invariably fails while trying to mysteriously install functools32. I've already spent weeks try to make PyGradle work with Python 3. Shouldn't it just work out of the box since Py2 is not supported anymore?

> Task :lsystems:installBuildRequirements
Error building package wheel using `[/Users/umayr/Code/sketchy-polytopes/python/lsystems/build/venv/bin/python, /Users/umayr/Code/sketchy-polytopes/python/lsystems/build/venv/bin/pip, wheel, --disable-pip-version-check, --wheel-dir, /Users/umayr/Code/sketchy-polytopes/python/lsystems/build/wheel-cache, --no-deps, /Users/umayr/.gradle/caches/modules-2/files-2.1/pypi/functools32/3.2.3-2/a520082a56af52c7af8d2d1390856bf1a0d755df/functools32-3.2.3-2.tar.gz]`
Processing /Users/umayr/.gradle/caches/modules-2/files-2.1/pypi/functools32/3.2.3-2/a520082a56af52c7af8d2d1390856bf1a0d755df/functools32-3.2.3-2.tar.gz
    Complete output from command python setup.py egg_info:
    This backport is for Python 2.7 only.
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/k6/wgpy0_d135x_8qfrvxr3qf680000gn/T/pip-req-build-p3v1ks18/
Error installing package using `[/Users/umayr/Code/sketchy-polytopes/python/lsystems/build/venv/bin/python, /Users/umayr/Code/sketchy-polytopes/python/lsystems/build/venv/bin/pip, install, --disable-pip-version-check, --no-deps, --upgrade, --ignore-installed, /Users/umayr/.gradle/caches/modules-2/files-2.1/pypi/functools32/3.2.3-2/a520082a56af52c7af8d2d1390856bf1a0d755df/functools32-3.2.3-2.tar.gz]`
Processing /Users/umayr/.gradle/caches/modules-2/files-2.1/pypi/functools32/3.2.3-2/a520082a56af52c7af8d2d1390856bf1a0d755df/functools32-3.2.3-2.tar.gz
    Complete output from command python setup.py egg_info:
    This backport is for Python 2.7 only.
    
    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/k6/wgpy0_d135x_8qfrvxr3qf680000gn/T/pip-req-build-awjoo6f3/

> Task :lsystems:installBuildRequirements FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':lsystems:installBuildRequirements'.
> Failed to install functools32-3.2.3-2. Please see above output for reason, or re-run your build using ``gradle -i build`` for additional logging.

build.gradle:

version = "0.1"
description = "Python Projects"

buildscript {
    repositories {
        mavenLocal()
        maven {
            url "https://plugins.gradle.org/m2/"
        }
        mavenCentral()
        jcenter()
    }
    dependencies {
        classpath group: 'com.linkedin.pygradle', name: 'pygradle-plugin', version: '0.12.10'
    }
}

subprojects {
    apply plugin: "idea"
    apply plugin: 'com.linkedin.python'
    apply plugin: 'com.linkedin.python-sdist'
    apply plugin: 'com.linkedin.python-cli'

    idea {
        module {
            sourceDirs += file('src')
            testSourceDirs += file('test')
        }
    }

    python {
        details {
            pythonVersion = '3.7'
            details.pythonVersion = '3.7'
        }
        // Sphinx-1.8.1.dist-info/METADATA:Requires-Dist: enum34; (python_version<"3")
        // enum34-1.1.6 causes the build to fail on Python 3. These versions are old but
        // the latest ones available at https://linkedin.jfrog.io/linkedin/pypi-external/pypi/
        // as of 2020-05-25.
        forceVersion('pypi', 'pip3', '21.0.1')
        forceVersion('pypi', 'flake8', '3.7.9')
        forceVersion('pypi', 'Sphinx', '2.2.1')
    }

    dependencies {
        python ('pypi:flake8:3.7.9') {
            exclude module: 'functools32'
        }
        python ('pypi:matplotlib:3.3.4') {
            exclude module: 'functools32'
        }
        python ('pypi:numpy:1.19.1') {
            exclude module: 'functools32'
        }
    }

    repositories {
        pyGradlePyPi()
        ivy {
            // Can't easily use a "global" local repo since
            // pivy-importer clobbers pre-existing libraries, which
            // could possibly create build problems for other packages
            // when builds are running in parallel.
            url "build/local-ivy-repo"
            layout('pattern') {
                ivy "[organisation]/[module]/[revision]/[module]-[revision].ivy"
                artifact "[organisation]/[module]/[revision]/[artifact]-[revision](-[classifier]).[ext]"
                m2compatible true
            }
        }
    }

    // Workaround due to PyGradle's lack of support for native PyPi repos
    task pipInstallRequirements(type: Exec) {
        commandLine "bash", "-c", "source build/venv/bin/activate && pip3 install -r requirements.txt && deactivate"
    }

    task pipInstallRequests(type: Exec) {
        commandLine  "pip3", "install", "--user", "requests"
    }

    // TODO: Offline test requires  gradle check -x getRequirements since
    // we're clobbering the local Ivy repo every time
    task getRequirements(type: Exec) {
        dependsOn pipInstallRequests
        commandLine "python3", "../etc/get_requirements.py", "build/local-ivy-repo"
        standardOutput = new ByteArrayOutputStream()
        ext.output = {
            return standardOutput.toString()
        }
    }

    task printReq {
        dependsOn getRequirements
        println tasks.getRequirements.output()
    }

    task printExternalDependencies {
        // it would be nice for setup.py to reference these
        // dependencies, and, separately, to use `pip freeze`
        // to write a requirements.txt
        doLast {
            println(project.configurations.python.allDependencies)
        }
    }

    installBuildRequirements.dependsOn getRequirements
}

Start with the installBuildRequirements task and the provided build.gradle, then inspect etc/get_requirements.py to trace how Python 3.7 dependencies are resolved. Reproduce the failure and determine why functools32 is selected; done means the Python 3 build no longer attempts to install this Python 2.7-only package and the task completes.