C:\Users\user1\Downloads>poetry new mpl
Created package mpl in mpl

C:\Users\user1\Downloads>cd mpl

C:\Users\user1\Downloads\mpl>poetry add matplotlib
Creating virtualenv mpl-py3.7 in C:\Users\user1\AppData\Local\pypoetry\Cache\virtualenvs
Using version ^3.1 for matplotlib

Updating dependencies
Resolving dependencies...

Writing lock file


Package operations: 16 installs, 0 updates, 0 removals

  - Installing zipp (0.5.1)
  - Installing importlib-metadata (0.18)
  - Installing six (1.12.0)
  - Installing atomicwrites (1.3.0)
  - Installing attrs (19.1.0)
  - Installing colorama (0.4.1)
  - Installing cycler (0.10.0)
  - Installing kiwisolver (1.1.0)
  - Installing more-itertools (7.0.0)
  - Installing numpy (1.16.4)
  - Installing pluggy (0.12.0)
  - Installing py (1.8.0)
  - Installing pyparsing (2.4.0)
  - Installing python-dateutil (2.8.0)
  - Installing matplotlib (3.1.0)
  - Installing pytest (3.10.1)

C:\Users\user1\Downloads\mpl>poetry run python
Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import matplotlib
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\user1\AppData\Local\pypoetry\Cache\virtualenvs\mpl-py3.7\lib\site-packages\matplotlib\__init__.py", line 200, in <module>
    _check_versions()
  File "C:\Users\user1\AppData\Local\pypoetry\Cache\virtualenvs\mpl-py3.7\lib\site-packages\matplotlib\__init__.py", line 194, in _check_versions
    module = importlib.import_module(modname)
  File "C:\Users\user1\AppData\Local\Programs\Python\Python37\lib\importlib\__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
ImportError: DLL load failed: The specified module could not be found.
>>> import sys
>>> print(sys.path)
['', 'C:\\Users\\user1\\AppData\\Local\\Programs\\Python\\Python37\\python37.zip', 'C:\\Users\\user1\\AppData\\Local\\Programs\\Python\\Python37\\DLLs', 'C:\\Users\\user1\\AppData\\Local\\Programs\\Python\\Python37\\lib', 'C:\\Users\\user1\\AppData\\Local\\Programs\\Python\\Python37', 'C:\\Users\\user1\\AppData\\Local\\pypoetry\\Cache\\virtualenvs\\mpl-py3.7', 'C:\\Users\\user1\\AppData\\Local\\pypoetry\\Cache\\virtualenvs\\mpl-py3.7\\lib\\site-packages']