fix(tidy3d): lazy load scipy to reduce import time

[frederikschubertflex]

Move scipy into the functions where it is used to reduce the import time. Related to #2422 and #2087. pandas or other libraries are more involved due to cross-dependencies via xarray, so I focused on this instead.

python -X importtime -c "from tidy3d import Simulation"

Before

import time: self [us] | cumulative | imported package
...
import time:      1429 |    1165589 | tidy3d

After

import time: self [us] | cumulative | imported package
...
import time:      1523 |     919501 | tidy3d

[github-actions]

Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/components/dispersion_fitter.py (100%)
• tidy3d/components/geometry/base.py (0.0%): Missing lines 1389
• tidy3d/components/medium.py (100%)
• tidy3d/components/mode/derivatives.py (100%)
• tidy3d/components/mode/solver.py (84.6%): Missing lines 32,904
• tidy3d/material_library/parametric_materials.py (60.0%): Missing lines 233-234
• tidy3d/plugins/autograd/primitives/interpolate.py (100%)
• tidy3d/plugins/design/method.py (87.5%): Missing lines 17
• tidy3d/plugins/dispersion/fit.py (100%)
• tidy3d/plugins/microwave/lobe_measurer.py (100%)
• tidy3d/plugins/resonance/resonance.py (100%)

Summary

• Total: 44 lines
• Missing: 6 lines
• Coverage: 86%

tidy3d/components/geometry/base.py

  1385         """
  1386         import gdstk
  1387 
  1388         if not isinstance(cell, gdstk.Cell):
! 1389             if "gdstk" in cell.__class__.__name__.lower():
  1390                 raise Tidy3dImportError(
  1391                     "Module 'gdstk' not found. It is required to export shapes to gdstk cells."
  1392                 )
  1393             raise Tidy3dImportError("Argument 'cell' must be an instance of 'gdstk.Cell'.")

---

tidy3d/components/mode/solver.py

  28 # double precision. This value is very heuristic.
  29 GOOD_CONDUCTOR_CUT_OFF = 1e70
  30 
  31 if TYPE_CHECKING:
! 32     from scipy import sparse as sp
  33 
  34 # Consider a material to be good conductor if |ep| (or |mu|) > GOOD_CONDUCTOR_THRESHOLD * |pec_val|
  35 GOOD_CONDUCTOR_THRESHOLD = 0.9

---

  900         if isinstance(vec_or_mat, csr_matrix):
  901             mat_norm = spl.norm(vec_or_mat)
  902             mat_imag_norm = spl.norm(vec_or_mat.imag)
  903             return mat_imag_norm / (mat_norm + fp_eps) > tol
! 904         raise RuntimeError(
  905             f"Variable type should be either numpy array or scipy.sparse.csr_matrix, got {type(vec_or_mat)}."
  906         )
  907 
  908     @classmethod

---

tidy3d/material_library/parametric_materials.py

  229         try:
  230             from scipy import integrate
  231 
  232             INTEGRATE_AVAILABLE = True
! 233         except ImportError:
! 234             INTEGRATE_AVAILABLE = False
  235 
  236         def fermi(E: float) -> float:
  237             """Fermi distribution."""
  238             # catch overflow warning

---

tidy3d/plugins/design/method.py

  13 
  14 from .parameter import ParameterAny, ParameterFloat, ParameterInt, ParameterType
  15 
  16 if TYPE_CHECKING:
! 17     from scipy.stats import qmc as qmc_type
  18 
  19 
  20 class Method(Tidy3dBaseModel, ABC):
  21     """Spec for a sweep algorithm, with a method to run it."""

---

[daquinteroflex]

Looks good! One in