scikit-learn: scikit_learn==0.21.0 is not available causing build issue in Google bazel based project

for me the replacement of sklearn==0.19.1 to scikit-learn==0.19.1 made the trick. Probably the same with another version of scikit-learn. I meet this issue while switching from python 2 to 3

Actually, we are using bazel with pipfile, somehow it is calculating 0.21.0 as dependencies based on dependencies graph which is not in our control. We do not install anything manually, our system calculates dependencies based on other dependencies, Error:

Building custom python environment for prediction_service failed (Exit 1)

Installing dependencies from Pipfile.lock (08b30c)���

An error occurred while installing scikit-learn==0.21.0 --hash=sha256:1a6e69128d1fe413a5722404756c62aac21d2f8a523beb57912afffc3640a75f --hash=sha256:2244785eb38f81c4c640d6e46594d950a92f6cc14351ba4926ed9351e6c16e3a --hash=sha256:2ae8b0e40fb044844b02af9d348bc1a2254b3f7b94151cc197536e1211b9280b --hash=sha256:4e39608650180d879b17fd7b47b1311f06a45630a8568173c1a22233b2dbbc73 --hash=sha256:5fc9a555752185e5698cfadfbedf75eae89887c2a8fc842d3976a2251ca53f49 --hash=sha256:615e2e953cae5b99530d0fc46c0227101956c7f33a99f78f237aba92f2a571b7 --hash=sha256:7afd99f1fa3daa67ecef97466b38b607bc6b7f611980687b444889a64ab55bff --hash=sha256:8447c5da132a0912679ec4e589547e83c42dc7979df2b1fd042c7638dcd002d5 --hash=sha256:8ff36dc5e0488f345a65ad514a6d9026bf1ec509f66d09d605acfdb61e8fbefa --hash=sha256:9a637d61645f9319caf6a9659b37c3e66110465e4455085fba804dfabc121518 --hash=sha256:ad1f354246148f7d054602704b6eb9b8437c09614629562789dce8ae808a63cb --hash=sha256:d2beb434bc8c5970372f391ced4480eb01ed46ac36d99684ec5da27500de50bc --hash=sha256:d46ce509c5be72bf15bdfc1faead1df681fa1cb0aa13468d53964941cd80add4 --hash=sha256:e6e46f5c0bf8a5666aa2656b9bbd630a07b3607bece116baccb548c8331dd9e0 --hash=sha256:f0ca67c81bf9abf65b5e8990854739b61d8f9d5d6c8e0b7477524dbbf03cb435! Will try again.

Installing initially failed dependencies���

Collecting scikit-learn==0.21.0
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DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7.

  ERROR: Could not find a version that satisfies the requirement scikit-learn==0.21.0 (from -r /home/jenkins/.cache/bazel/_bazel_jenkins/ffdeb2a7c6282981ce42e3c9eb3f5057/execroot/__main__/tmpb35_a5b8ec1a4863cad5/pipenv-WbxC4F-requirements/pipenv-Lsc_75-requirement.txt (line 1)) (from versions: 0.9, 0.10, 0.11, 0.12, 0.12.1, 0.13, 0.13.1, 0.14, 0.14.1, 0.15.0b1, 0.15.0b2, 0.15.0, 0.15.1, 0.15.2, 0.16b1, 0.16.0, 0.16.1, 0.17b1, 0.17, 0.17.1, 0.18rc2, 0.18, 0.18.1, 0.18.2, 0.19b2, 0.19.0, 0.19.1, 0.19.2, 0.20rc1, 0.20.0, 0.20.1, 0.20.2, 0.20.3, 0.21rc2)

ERROR: No matching distribution found for scikit-learn==0.21.0 (from -r /home/jenkins/.cache/bazel/_bazel_jenkins/ffdeb2a7c6282981ce42e3c9eb3f5057/execroot/__main__/tmpb35_a5b8ec1a4863cad5/pipenv-WbxC4F-requirements/pipenv-Lsc_75-requirement.txt (line 1))