specify pip version in bitbucket_pipelines.yml file

[Ye_He]

hi, 

I have the following pipelines files

pipelines:
   bookmarks: live-*: 
      - step: 
        name: Test 
        caches: - pip 
        script: - bash sdlc_test.sh

 currently, I believe the pip in my cache is newer than pip 10.0

therefore it throws the errors as this stackoverflow question asks. 

AttributeError: Module Pip has no attribute 'main'

I wonder if there is a way to specify a specific pip version like pip 9.0.3 in the bitbucket_pipeline.yml file so the pipline runs with a specific pip version? Thanks.