Virtualenv gives a clean working environment for python project. To understand virtualenv, we need to understand how python works,
- When you execute
python binary in command line,
- It implicitly read site.py (defaults to
- Sets sys.prefix and this sys.prefix(platform independent packages) and sys.exec_prefix(platform dependent packages)
- Sets sys.path and these variable decide where the packages will go.
How it sets sys.prefix (in-order to precedence) ??
- Check for PYTHONHOME variable, if this variable is set than value of $PYTHONHOME is sys.prefix and all packages will go in that directory.
- Look for landmark(in python’s case os.py file) lib/python$version/os.py and where it finds this relative path structure that is sys.prefix
- Else whatever value is fixed during compile time.
- A simpler of virtualenv will do is:
- copy python binary in your project location(e.g.
- you need to have directory structure like $LOCATION/lib/python$version/os.py
- python/pip binary at $LOCATION will put all those packages to *$LOCATION/lib/python$version/site-packages/ *.
What bin/activate does: It calls your copied python/pip binary instead of system binary, so that it sets sys.prefix to your specified directory and install packages over there.
By default python puts packages to global location i.e. /usr/lib/python$version/site-packages
- To find sys.prefix use:
python -c "import sys; print sys.prefix"
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