PuLP not printing output on IPython cell

Question

I am using PuLP and IPython/Jupyter Notebook for a project.

I have the following cell of code:

import pulp
model = pulp.LpProblem('Example', pulp.LpMinimize)
x1 = pulp.LpVariable('x1', lowBound=0, cat='Integer')
x2 = pulp.LpVariable('x2', lowBound=0, cat='Integer')

model += -2*x1 - 3*x2 
model += x1 + 2*x2 <= 7
model += 2*x1 + x2 <= 7
model.solve(pulp.solvers.COIN(msg=True))

When I execute the cell, the output is simply:

When I look at the terminal running the Notebook server, I can see the output of the solver (in this case: COIN). The same happens if a change the model.solve argument to

model.solve(pulp.solvers.PULP_CBC_CMD(msg=True))

or

model.solve(pulp.solvers.PYGLPK(msg=True))

However, when I use the Gurobi Solver, with the line

model.solve(pulp.solvers.GUROBI(msg=True))

the output of the solver is displayed on the Notebook cell, which is the behavior I want. In fact, I would be happy with any free solver printing its output directly on the Notebook cell.

I could not find directions on how to approach this issue in PuLP documentation. Any help would be appreciated. I am also curious to know if someone else gets this behavior.

I am using Linux Mint, 64 Bits, IPython 4.0.0 and PuLP 1.6.0.

Asked By: pbc1303

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Source

Answer 1

Use %%python cell magic to print terminal’s output.

%%python
import pulp
model = pulp.LpProblem('Example', pulp.LpMinimize)
x1 = pulp.LpVariable('x1', lowBound=0, cat='Integer')
x2 = pulp.LpVariable('x2', lowBound=0, cat='Integer')

model += -2*x1 - 3*x2 
model += x1 + 2*x2 <= 7
model += 2*x1 + x2 <= 7

model.solve(pulp.solvers.COIN(msg=True))

Answered By: serge_k

Answer 2

Late to the party, but for anyone still looking for a solution…

Create a file called monkeypatch.py and put it in the same directory as your notebooks

Paste the following into it, and save

from pulp import PULP_CBC_CMD, LpProblem

original_solve_method = LpProblem.solve

def solve(prob):
    solver = PULP_CBC_CMD(logPath=r'log.txt', msg=False)
    original_solve_method(prob, solver=solver)
    with open('log.txt', 'r') as f:
        print(f.read())

LpProblem.solve = solve

Then in your notebook insert the line

import monkeypatch

near the top.

It will overwrite the solve method, so that it writes the logfile to "log.txt" and then reads in this file and displays it inside the notebook.

Answered By: Riley

PuLP not printing output on IPython cell

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