How to fix 'C extension not loaded, training will be slow. Install a C compiler and reinstall gensim for fast training.'
For me, degrading back to Gensim version 3.7.1 from 3.7.3 worked.
I'm using the library node2vec, which is based on gensim word2vec model to encode nodes in an embedding space, but when i want to fit the word2vec object I get this warning:

C:\Users\lenovo\Anaconda3\lib\site-packages\gensim\models\base_any2vec.py:743:
  UserWarning: C extension not loaded, training will be slow. Install a
  C compiler and reinstall gensim for fast training.

Can any one help me to fix this issue please ?