Fix - prevent zero of log and set ef_construction arg in build()

[kwangswei]

Thanks for your contribution :) Before you submit this pull request, please ensure it is against the dev branch and not master.

• [v] ensure branch where you submitting, it sould be dev.
• [v] check your coding convension.
  • 4 spaces for indentation
  • pep8 for Python

[kwangswei]

Ooops, sorry for typo. I will re-submit.