Getting ImportError: no module named 'sklearn' when installing auto-sklearn

Question

Why do I get ImportError: No module named 'sklearn' when installing auto-sklearn via pip?

 $ virtualenv -p python3 automl $ cd automl/ $ source bin/activate $ pip install auto-sklearn Collecting auto-sklearn Downloading auto-sklearn-0.1.1.tar.gz (5.9MB) 100% |████████████████████████████████| 5.9MB 265kB/s Complete output from command python setup.py egg_info: Traceback (most recent call last): File "<string>", line 1, in <module> File "/tmp/pip-build-whq6xjt6/auto-sklearn/setup.py", line 2, in <module> import autosklearn File "/tmp/pip-build-whq6xjt6/auto-sklearn/autosklearn/__init__.py", line 2, in <module> from autosklearn.util import dependencies File "/tmp/pip-build-whq6xjt6/auto-sklearn/autosklearn/util/__init__.py", line 4, in <module> from .common import * File "/tmp/pip-build-whq6xjt6/auto-sklearn/autosklearn/util/common.py", line 4, in <module> from sklearn.externals import six ImportError: No module named 'sklearn' ---------------------------------------- Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-whq6xjt6/auto-sklearn/ 

There seems to be no dependencies in the pip distribution. But why doesn't automatic dependency installation work? I can set auto-sklearn this way:

 $ wget https://raw.githubusercontent.com/automl/auto-sklearn/master/requirements.txt $ pip install -r requirements.txt $ pip install numpy six Cython # something goes wrong here too!? $ pip install -r requirements.txt $ pip install auto-sklearn 

I looked at the tar tar tar file at https://pypi.python.org/pypi/auto-sklearn/0.1.1 , and the install_requires in setup.py seems to me ok, Does MANIFEST.in string?

I posed a GitHub question for this at https://github.com/automl/auto-sklearn/issues/206 , but it was closed. What is the reason for such a manual installation?