Using a particular python binary with venv

[greenbay . graham]

According to this https://docs.python.org/3.4/library/venv.html#module-venv 
'Each virtual environment has its own Python binary (allowing creation of 
environments with various Python versions)' 
So how would I create a virtual environment using the venv module that has a 
Python 2.7 binary?
tia
g
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