pip list is a shell command. You should run it in your shell (bash/cmd), rather than invoke it from python interpreter.
pip does not provide a stable API. The only supported way of calling it is via subprocess, see docs and the code at the end of this answer.
However, if you want to just check if pip exists locally, without running it, and you are running Linux, I would suggest that you use bash's which command:
which pip
It should show you whether the command can be found in bash's PATH/aliases, and if it does, what does it actually execute.
If running pip is not an issue, you could just do:
python -m pip --version
If you really need to do it from a python script, you can always put the import statement into a try...except block:
try:
import pip
except ImportError:
print("Pip not present.")
Or check what's the output of a pip --version using subprocess module:
subprocess.check_call([sys.executable, '-m', 'pip', '--version'])