BUG: Pandas 1.2.0 not importing numpy
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Collecting pandas
222
  Downloading http://*private-pypi-repo*/root/pypi/%2Bf/e03/386615b970b8b/pandas-1.2.0.tar.gz (5.4 MB)
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  Installing build dependencies: started
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  Installing build dependencies: finished with status 'done'
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  Getting requirements to build wheel: started
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  Getting requirements to build wheel: finished with status 'error'
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  ERROR: Command errored out with exit status 1:
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   command: /usr/local/bin/python /usr/local/lib/python3.6/site-packages/pip/_vendor/pep517/_in_process.py get_requires_for_build_wheel /tmp/tmpyzo8hnvu
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       cwd: /tmp/pip-install-wsvw3tn6/pandas_0107e3e2e0984808803b03b19130c9e4
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  Complete output (18 lines):
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  Traceback (most recent call last):
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    File "/usr/local/lib/python3.6/site-packages/pip/_vendor/pep517/_in_process.py", line 280, in <module>
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      main()
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    File "/usr/local/lib/python3.6/site-packages/pip/_vendor/pep517/_in_process.py", line 263, in main
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      json_out['return_val'] = hook(**hook_input['kwargs'])
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    File "/usr/local/lib/python3.6/site-packages/pip/_vendor/pep517/_in_process.py", line 114, in get_requires_for_build_wheel
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      return hook(config_settings)
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    File "/tmp/pip-build-env-isjnq9ut/overlay/lib/python3.6/site-packages/setuptools/build_meta.py", line 150, in get_requires_for_build_wheel
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      config_settings, requirements=['wheel'])
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    File "/tmp/pip-build-env-isjnq9ut/overlay/lib/python3.6/site-packages/setuptools/build_meta.py", line 130, in _get_build_requires
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      self.run_setup()
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    File "/tmp/pip-build-env-isjnq9ut/overlay/lib/python3.6/site-packages/setuptools/build_meta.py", line 254, in run_setup
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      self).run_setup(setup_script=setup_script)
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    File "/tmp/pip-build-env-isjnq9ut/overlay/lib/python3.6/site-packages/setuptools/build_meta.py", line 145, in run_setup
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      exec(compile(code, __file__, 'exec'), locals())
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    File "setup.py", line 20, in <module>
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      import numpy
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  ModuleNotFoundError: No module named 'numpy'

#### Problem description

When I am downloading pandas 1.2.0 to build my docker image for my python project, I am getting the following error above. Numpy seems to be not importing for some reason. The excepted output would be what was when I building the image yesterday (before the release)

I am using the following command to download my requirements: 
RUN pip install --no-cache-dir -r requirements.txt --extra-index-url $INDEX_URL --trusted-host $TRUSTED_HOST_URL

And the requirements.txt is as follows:
connexion
python_dateutil
setuptools
Flask-Testing
libmctwist >= 1.0.0
swagger-ui-bundle

libmctwist requirements.txt contains:
libinfinityd >= 1.1.0
azure-cosmos

libinfinityd requirements.txt contains:
pandas
requests
pyyaml
six
mysql-connector-python

I've tried altering libinfinityd's requirements.txt to contain NumPy, at this point though, I think I'm going to revert to pandas 1.1.5 in the libinfinityd's requirements.txt 

#### Expected Output

Collecting pandas
214
  Downloading http://*private-pypi-repo*/root/pypi/%2Bf/f10/fc41ee3c75a47/pandas-1.1.5.tar.gz (5.2 MB)
215
  Installing build dependencies: started
216
  Installing build dependencies: still running...
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  Installing build dependencies: still running...
218
  Installing build dependencies: still running...
219
  Installing build dependencies: finished with status 'done'
220
  Getting requirements to build wheel: started
221
  Getting requirements to build wheel: still running...
222
  Getting requirements to build wheel: finished with status 'done'
223
    Preparing wheel metadata: started
224
    Preparing wheel metadata: finished with status 'done'
225
WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ReadTimeoutError("HTTPSConnectionPool(host='pypi.org', port=443): Read timed out. (read timeout=15)",)': /simple/pytz/
