correct cube_root function. Use _dummy module to avoid type: ignore

Author: scivision

src/pymap3d/_dummy.py

@@ -0,0 +1,7 @@
+from datetime import datetime
+
+def eci2ecef(x, y, z, time: datetime, force_non_astropy: bool = False) -> tuple:
+    raise ImportError("Numpy required for eci2ecef")
+
+def ecef2eci(x, y, z, time: datetime, force_non_astropy: bool = False) -> tuple:
+    raise ImportError("Numpy required for ecef2eci")

src/pymap3d/aer.py

@@ -11,12 +11,7 @@
 try:
     from .eci import ecef2eci, eci2ecef
 except ImportError:
-
-    def eci2ecef(x, y, z, time: datetime, force_non_astropy: bool = False) -> tuple:
-        raise ImportError("Numpy required for eci2ecef")
-
-    def ecef2eci(x, y, z, time: datetime, force_non_astropy: bool = False) -> tuple:
-        raise ImportError("Numpy required for ecef2eci")
+    from ._dummy import ecef2eci, eci2ecef
 
 
 __all__ = ["aer2ecef", "ecef2aer", "geodetic2aer", "aer2geodetic", "eci2aer", "aer2eci"]

src/pymap3d/mathfun.py

@@ -71,21 +71,14 @@ def sign(x) -> float:  # type: ignore
 
         return y
 
-    try:
-        import math.cbrt as cbrt  # type: ignore
-    except ImportError:
-
-        def cbrt(x) -> float:  # type: ignore
-            return x ** (1 / 3)
-
 
 __all__ = [
     "asin",
     "asinh",
     "atan",
     "atan2",
     "atanh",
-    "cbrt",
+    "cube_root",
     "cos",
     "degrees",
     "exp",
@@ -101,3 +94,14 @@ def cbrt(x) -> float:  # type: ignore
     "sqrt",
     "tan",
 ]
+
+
+def cube_root(x):
+    """cube root function, handles negative numbers"""
+    try:
+        return cbrt(x)
+    except NameError:
+        if x < 0:
+            return -power(-x, 1.0 / 3.0)
+        else:
+            return power(x, 1.0 / 3.0)

src/pymap3d/spherical.py

@@ -7,7 +7,7 @@
 from __future__ import annotations
 
 from .ellipsoid import Ellipsoid
-from .mathfun import asin, atan2, cbrt, degrees, hypot, power, radians, sin, sqrt
+from .mathfun import asin, atan2, cube_root, degrees, hypot, power, radians, sin, sqrt
 
 __all__ = [
     "geodetic2spherical",
@@ -145,7 +145,7 @@ def spherical2geodetic(
     q_0 = (1 - ell.eccentricity**2) / ell.semimajor_axis**2 * Z**2
     r_0 = (p_0 + q_0 - ell.eccentricity**4) / 6
     s_0 = ell.eccentricity**4 * p_0 * q_0 / 4 / r_0**3
-    t_0 = cbrt(1 + s_0 + sqrt(2 * s_0 + s_0**2))
+    t_0 = cube_root(1 + s_0 + sqrt(2 * s_0 + s_0**2))
     u_0 = r_0 * (1 + t_0 + 1 / t_0)
     v_0 = sqrt(u_0**2 + q_0 * ell.eccentricity**4)
     w_0 = ell.eccentricity**2 * (u_0 + v_0 - q_0) / 2 / v_0