code: def nancov(
      a: np.ndarray,
      b: np.ndarray,
      *,
      min_periods: int | None = None,
      ddof: int | None = 1,
  ) -> float:
      if len(a) != len(b):
          raise AssertionError("Operands to nancov must have same size")
  
      if min_periods is None:
          min_periods = 1
  
      valid = notna(a) & notna(b)
      if not valid.all():
          a = a[valid]
          b = b[valid]
  
      if len(a) < min_periods:
          return np.nan
  
      return np.cov(a, b, ddof=ddof)[0, 1]
  
imports: from __future__ import annotations
  import functools
  import itertools
  import operator
  from typing import Any, Callable, cast
  import warnings
  import numpy
  from pandas._config import get_option
  from pandas._libs import NaT, NaTType, iNaT, lib
  from pandas._typing import ArrayLike, AxisInt, CorrelationMethod, Dtype, DtypeObj, F, Scalar, Shape, npt
  from pandas.compat._optional import import_optional_dependency
  from pandas.util._exceptions import find_stack_level
  from pandas.core.dtypes.common import is_any_int_dtype, is_bool_dtype, is_complex, is_datetime64_any_dtype, is_float, is_float_dtype, is_integer, is_integer_dtype, is_numeric_dtype, is_object_dtype, is_scalar, is_timedelta64_dtype, needs_i8_conversion, pandas_dtype
  from pandas.core.dtypes.dtypes import PeriodDtype
  from pandas.core.dtypes.missing import isna, na_value_for_dtype, notna
  from pandas.core.construction import extract_array
label_desc: Use image node_id 36 for calling a global function with example usage: nancov(a, b) and returns: np, np