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== Using Gurobi in Python virtual environments ==
== Using Gurobi in Python virtual environments ==


Gurobi brings it's own version of Python but that one does not contain any 3rd-party Python packages except Gurobi.  In order to use Gurobi together with popular Python
packages like NumPy, Matplotlib, Pandas and others, we need to create a [[Python#Creating_and_using_a_virtual_environment|virtual Python environment]]in which we can install both <code>gurobipy</code> and e.g. <code>pandas</code>.


Before we start, we need to decide which combination of versions for Gurobi and Python to use.
{{Commands|prompt=[name@server ~] $
|module load gurobi/8.1.1
|cd $EBROOTGUROBI/lib
|ls -dF python*
  python2.7/        python2.7_utf32/  python3.6_utf32/
  python2.7_utf16/  python3.5_utf32/  python3.7_utf32/
 
|module load gurobi/9.0.1
|cd $EBROOTGUROBI/lib
|ls -dF python*
  python2.7_utf16/  python3.5_utf32/  python3.7/        python3.8_utf32/
  python2.7_utf32/  python3.6_utf32/  python3.7_utf32/
 
|cd
}}
We see that <code>gurobi/8.1.1</code> brings it's own installation of <code>python2.7/</code> and Python packages for Python 2.7, 3.5, 3.6 and 3.7 (<code>pythonX.Y_utf32/</code>),
while <code>gurobi/9.0.1</code> by default uses <code>python3.7/</code> and brings Python packages for Python 2.7, 3.5, 3.6, 3.7 and 3.8 (<code>pythonX.Y_utf32/</code>).
In this example we want to create a Python environment based on <code>python/3.7</code> in which we want to use <code>gurobi/9.0.1</code> and install the Pandas package.
=== Creating a Python virtual environments with Gurobi ===
These steps need to be done only once per system.
The first step is to load the modules, [[Python#Creating_and_using_a_virtual_environment|create the virtual environment]] and activate it.
{{Commands|prompt=[name@server ~] $
| module load gurobi/9.0.1 python/3.7
| virtualenv --no-download  ~/env_gurobi
  Using base prefix '/cvmfs/soft.computecanada.ca/easybuild/software/2017/Core/python/3.7.4'
  New python executable in /home/name/env_gurobi/bin/python
  Installing setuptools, pip, wheel...
  done.
| source ~/env_gurobi/bin/activate
}}
Now that the environment has been activated we can install the Python packages we want to use, in this case <code>pandas</code>.
{{Commands|prompt=(env_gurobi) [name@server ~] $
| pip install --no-index  pandas
  Ignoring pip: markers 'python_version < "3"' don't match your environment
  Looking in links: /cvmfs/soft.computecanada.ca/custom/python/wheelhouse/nix/avx2, /cvmfs/soft.computecanada.ca/custom/python/wheelhouse/nix/generic, /  cvmfs/soft.computecanada.ca/custom/python/wheelhouse/generic
  Collecting pandas
  Collecting numpy>=1.13.3 (from pandas)
  [...]
  Successfully installed numpy-1.18.4 pandas-1.0.3 python-dateutil-2.8.1 pytz-2020.1 six-1.15.0
}}
The third step is to install gurobipy into the environment:
{{Commands|prompt=(env_gurobi) [name@server ~] $
| cd $EBROOTGUROBI
| python setup.py build --build-base /dev/shm/${USER} install
  running build
  running build_py
  creating /dev/shm/name
  creating /dev/shm/name/lib
  creating /dev/shm/name/lib/gurobipy
  copying lib/python3.7_utf32/gurobipy/__init__.py -> /dev/shm/name/lib/gurobipy
  copying lib/python3.7_utf32/gurobipy/gurobipy.so -> /dev/shm/name/lib/gurobipy
  running install
  running install_lib
  creating /home/name/env_gurobi/lib/python3.7/site-packages/gurobipy
  copying /dev/shm/name/lib/gurobipy/gurobipy.so -> /home/name/env_gurobi/lib/python3.7/site-packages/gurobipy
  copying /dev/shm/name/lib/gurobipy/__init__.py -> /home/name/env_gurobi/lib/python3.7/site-packages/gurobipy
  byte-compiling /home/name/env_gurobi/lib/python3.7/site-packages/gurobipy/__init__.py to __init__.cpython-37.pyc
  running install_egg_info
  Writing /home/name/env_gurobi/lib/python3.7/site-packages/gurobipy-9.0.1-py3.7.egg-info
| cd
}}
=== Using the Gurobi-enabled virtual environment ===
Python scripts can now import both Pandas and Gurobi:
import pandas as pd
import numpy as np
import gurobipy as gurobi
from gurobipy import *
# [...]
Once created we can activate Gurobi and the environment with:
module load gurobi/8.1.1
source ~/env_gurobi/bin/activate
python  my_gurobi_script.py
Note that we now use <code>python</code> instead of <code>gurobi.sh</code>!
And this is an example job script that we can use:
{{File
  |name=gurobi-py_example.sh
  |lang="sh"
  |contents=
#!/bin/bash
#SBATCH --time=0-00:30        # time limit (D-HH:MM)
#SBATCH --cpus-per-task=1    # number of CPUs (threads) to use
#SBATCH --mem-per-cpu=1000M  # memory per CPU (in MB)
module purge
module load gurobi/9.0.1
source ~/env_gurobi/bin/activate
# Create environment file in current directory setting the number of threads:
echo "Threads ${SLURM_CPUS_ON_NODE:-1}" > gurobi.env
python  my_gurobi_script.py
}}


== Cite Gurobi ==
== Cite Gurobi ==


Please see [https://support.gurobi.com/hc/en-us/articles/360013195592-How-do-I-cite-Gurobi-software-for-an-academic-publication- How do I cite Gurobi software for an academic publication?]
Please see [https://support.gurobi.com/hc/en-us/articles/360013195592-How-do-I-cite-Gurobi-software-for-an-academic-publication- How do I cite Gurobi software for an academic publication?]
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