  Here is the Python code based on the given instructions:
```
import bluemira
import numpy as np

# Define parameters for the coil and enclosure
coil_radius = 0.1
coil_length = 0.2
enclosure_radius = 0.25
enclosure_length = 0.5

# Create the coil and enclosure using the bluemira library's geometry tools
coil = bluemira.Coil(coil_radius, coil_length)
enclosure = bluemira.Enclosure(enclosure_radius, enclosure_length)

# Set the mesh options for each
coil.set_mesh_options(mesh_size=0.01)
enclosure.set_mesh_options(mesh_size=0.01)

# Create components for the universe, enclosure, and coil
universe = bluemira.Universe()
universe.add_component(coil)
universe.add_component(enclosure)

# Create a mesh and convert it for use in the FEniCS library
mesh = bluemira.Mesh(universe)
fenics_mesh = mesh.to_fenics()

# Instantiate a magnetostatic solver and define the source term for the problem
solver = bluemira.MagnetostaticSolver(fenics_mesh)
source_term = bluemira.SourceTerm(fenics_mesh, np.array([0, 0, 1]))

# Solve the magnetostatic problem and calculate the magnetic field
solver.solve(source_term)
magnetic_field = solver.get_magnetic_field()

# Compare the calculated magnetic field with the theoretical value along the z-axis and along a radial path at a certain z-offset
z_offset = 0.1
radial_path = np.linspace(0, enclosure_radius, 100)

# Calculate the theoretical magnetic field along the z-axis
theoretical_magnetic_field_z = np.zeros(z_offset)
for i in range(z_offset):
    theoretical_magnetic_field_z[i] = np.sqrt(2 * np.pi * enclosure_radius ** 2) * np.exp(-(i - z_offset) ** 2 / (2 * enclosure_radius ** 2))

# Calculate the theoretical magnetic field along the radial path
theoretical_magnetic_field_radial = np.zeros(radial_path.size)
for i in range(radial_path.size):
    theoretical_magnetic_field_radial[i] = np.sqrt(2 * np.pi * enclosure_radius ** 2) * np.exp(-(radial_path[i] - enclosure_radius) ** 2 / (2 * enclosure_radius ** 2))

# Plot the calculated and theoretical magnetic fields
import matplotlib.pyplot as plt
plt.plot(z_offset, magnetic_field[z_offset], label='Calculated magnetic field along z-axis')
plt.plot(radial_path, magnetic_field[radial_path], label='Calculated magnetic field along radial path')
plt.plot(z_offset, theoretical_magnetic_field_z, label='Theoretical magnetic field along z-axis')
plt.plot(radial_path, theoretical_magnetic_field_radial, label='Theoretical magnetic field along radial path')
plt.legend()
plt.show()
```
Note that this code assumes that the `bluemira` library is installed and imported as `bluemira`. Additionally, this code assumes that the `numpy` library is also installed and imported as `np`.