  Here is the Python code based on the given instructions:
```
from dream import *

# Set up the simulation
sim = construct_A()

# Set the electric field strength
sim.setElectricFieldStrength(0.6)

# Set the electron density
sim.setElectronDensity(5e19)

# Set the temperature
sim.setTemperature(1e3)

# Set the ion species
sim.addIon('D', 1)

# Disable the hot-tail grid
sim.setHotTailGrid(False)

# Set the collision frequency mode to ultra-relativistic
sim.setCollisionFrequencyMode('ultra-relativistic')

# Include the Dreicer and avalanche effects
sim.setDreicer(True)
sim.setAvalanche(True)

# Set the avalanche mode to fluid
sim.setAvalancheMode('fluid')

# Set the Dreicer rate to neural network
sim.setDreicerRate('neural network')

# Set the initial profile to 1e15
sim.setInitialProfile(1e15)

# Enable the runaway electron grid
sim.setRunawayElectronGrid(True)

# Set the number of radial points
sim.setNumberOfRadialPoints(50)

# Set the number of momentum points
sim.setNumberOfMomentumPoints(100)

# Set the maximum momentum
sim.setMaximumMomentum(0.5)

# Set the advection interpolation method to use flux limiters
sim.setAdvectionInterpolationMethod('flux limiters')

# Set the initialization method to isotropic
sim.setInitializationMethod('isotropic')

# Set the radial grid
sim.setRadialGrid(5, 0.22, 0.22, 1)

# Set the solver to nonlinear and verbose
sim.setSolver('nonlinear', 'verbose')

# Set the relative tolerance for the runaway electron current density
sim.setRelativeTolerance(1e-4)

# Set the time stepper
sim.setTimeStepper(1e-1, 20)

# Save the settings to an HDF5 file
sim.saveSettings('dream_settings.h5')

# Run the simulation
sim.runSimulation()
```