  Here is the Python code based on the given instructions:
```
import numpy as np
import pandas as pd
from porepy import DarcyAndTransport, test_ismember_rows_double_occurence_a_and_b, TestGettersAndSetters, _uniquify_points_and_edges, _point_and_edge_lists, test_round_up_and_down, test_many_points_and_segments, test_single_point_and_segment, test_one_cell_a_time_node_keyword, _a_in_b, to_vtk, snap_to_grid, time_step, to_gmsh, SnapToGridTest, map_subgrid_to_grid, apply_function_to_edges, apply_function_to_nodes, fracture_to_plane, _face_vector_to_scalar

# Define functions for adding data to the grid bucket
def add_data_darcy(gb, tol):
    gb.add_data('permeability', np.array([[1, 0], [0, 1]]), tol)
    gb.add_data('source', np.array([[0, 0], [0, 0]]), tol)
    gb.add_data('aperture', np.array([[0, 0], [0, 0]]), tol)
    gb.add_data('boundary_conditions', np.array([[0, 0], [0, 0]]), tol)

def add_data_advection(gb, tol):
    gb.add_data('source', np.array([[0, 0], [0, 0]]), tol)
    gb.add_data('porosity', np.array([[0, 0], [0, 0]]), tol)
    gb.add_data('discharge', np.array([[0, 0], [0, 0]]), tol)
    gb.add_data('boundary_conditions', np.array([[0, 0], [0, 0]]), tol)

# Define variables for tolerance, export folder, time, number of time steps, time step size, export frequency, and coarsening
tol = 1e-6
export_folder = 'output'
time = 0
num_time_steps = 100
time_step_size = 0.01
export_frequency = 10
coarsening = True

# Define dictionaries for mesh size and domain boundaries
mesh_size = {'x': 10, 'y': 10}
domain_boundaries = {'x': [0, 10], 'y': [0, 10]}

# Import grid from CSV file, compute geometry, coarsen if necessary, and assign node ordering
grid = pd.read_csv('grid.csv')
grid = grid.assign(geometry=grid.apply(lambda row: np.array([row['x'], row['y']]), axis=1))
if coarsening:
    grid = grid.assign(geometry=grid.apply(lambda row: np.array([row['x'], row['y']]), axis=1))
grid = grid.assign(node_ordering=grid.apply(lambda row: np.array([row['x'], row['y']]), axis=1))

# Create Darcy solver, add Darcy data to the grid bucket, solve the Darcy problem, and extract and project the discharge and pressure
darcy_solver = DarcyAndTransport(grid, mesh_size, domain_boundaries)
add_data_darcy(darcy_solver.grid_bucket, tol)
darcy_solver.solve()
discharge = darcy_solver.grid_bucket.get_data('discharge')
pressure = darcy_solver.grid_bucket.get_data('pressure')

# Create advection and mass matrix solvers, add advection data to the grid bucket, and add a time step property to the grid bucket
advection_solver = DarcyAndTransport(grid, mesh_size, domain_boundaries)
add_data_advection(advection_solver.grid_bucket, tol)
advection_solver.grid_bucket.add_time_step_property()

# Create matrices and right-hand sides for the advection and mass matrix problems, and perform an LU factorization to speed up the solver
A = advection_solver.mass_matrix()
b = advection_solver.right_hand_side()
lu = np.linalg.lu_factor(A)

# Initialize solution vector and arrays for time and production, and loop over time steps to update the solution, compute the production, and export the solution to a VTK file every specified number of time steps
solution = np.zeros(grid.shape[0])
time_array = np.zeros(num_time_steps)
production_array = np.zeros(num_time_steps)
for i in range(num_time_steps):
    time_array[i] = time
    production_array[i] = np.sum(discharge[i])
    solution = np.linalg.lu_solve(lu, b)
    advection_solver.grid_bucket.set_data('solution', solution)
    advection_solver.grid_bucket.set_data('time', time)
    advection_solver.grid_bucket.set_data('production', production_array[i])
    to_vtk(advection_solver.grid_bucket, f'{export_folder}/solution_{i:04d}.vtk')
    time += time_step_size

# Export the time steps to a PVD file and save the times and absolute production values to a text file
to_pvd(advection_solver.grid_bucket, f'{export_folder}/solution.pvd')
with open(f'{export_folder}/production.txt', 'w') as f:
    for i in range(num_time_steps):
        f.write(f'{time_array[i]:.4f} {production_array[i]:.4f}\n')
```