refactor the uvbeam._convert_feeds_to_pols into a utility function

To enable wider use of the function (specifically in pyuvsim)

src/pyuvdata/analytic_beam.py

@@ -19,7 +19,7 @@
 
 from . import utils
 from .docstrings import combine_docstrings
-from .uvbeam.uvbeam import UVBeam, _convert_feeds_to_pols
+from .uvbeam.uvbeam import UVBeam
 
 __all__ = ["AnalyticBeam", "AiryBeam", "GaussianBeam", "ShortDipoleBeam", "UniformBeam"]
 
@@ -164,7 +164,7 @@ def __post_init__(self, include_cross_pols):
         if len(self.feed_array) == 1:
             include_cross_pols = False
 
-        self.polarization_array, _ = _convert_feeds_to_pols(
+        self.polarization_array = utils.convert_feeds_to_pols(
             self.feed_array, include_cross_pols, x_orientation=self.x_orientation
         )
 

src/pyuvdata/utils/pol.py

@@ -8,6 +8,7 @@
 from functools import lru_cache, wraps
 
 import numpy as np
+import numpy.typing as npt
 
 from . import tools
 
@@ -27,6 +28,7 @@
     "x_orientation_pol_map",
     "parse_polstr",
     "parse_jpolstr",
+    "convert_feeds_to_pols",
 ]
 
 # fmt: off
@@ -531,6 +533,57 @@ def determine_pol_order(pols, *, order="AIPS"):
     return index_array
 
 
+def convert_feeds_to_pols(
+    feed_array: npt.NDArray[str],
+    include_cross_pols: bool = True,
+    x_orientation: str | None = None,
+    return_feed_pol_order: bool = False,
+):
+    """
+    Get the polarizations given a feed array.
+
+    Parameters
+    ----------
+    feed_array : ndarray of str
+        Array of feed orientations. Options are: n/e or x/y or r/l.
+    include_cross_pols : bool
+        Option to include the cross polarizations (e.g. xy and yx or en and ne).
+        Defaults to True if more than one feed, set to False for only one feed.
+    x_orientation : str, optional
+        Orientation of the x-axis. Options are 'east', 'north', 'e', 'n', 'ew', 'ns'.
+    return_feed_pol_order : bool
+        Option to return a list of tuples giving the ordering of the feeds for
+        each pol. Default False.
+
+    """
+    n_feeds = np.asarray(feed_array).size
+
+    if n_feeds < 1 or n_feeds > 2:
+        raise ValueError(
+            "feed_array contains {n_feeds}. Only 1 or 2 feeds is supported."
+        )
+
+    feed_pol_order = [(0, 0)]
+    if n_feeds > 1:
+        feed_pol_order.append((1, 1))
+    else:
+        include_cross_pols = False
+
+    if include_cross_pols:
+        feed_pol_order.extend([(0, 1), (1, 0)])
+
+    pol_strings = []
+    for pair in feed_pol_order:
+        pol_strings.append(feed_array[pair[0]] + feed_array[pair[1]])
+    polarization_array = np.array(
+        [polstr2num(ps.upper(), x_orientation=x_orientation) for ps in pol_strings]
+    )
+    if return_feed_pol_order:
+        return polarization_array, feed_pol_order
+    else:
+        return polarization_array
+
+
 def _select_pol_helper(
     polarizations,
     obj_pol_array,

src/pyuvdata/uvbeam/initializers.py

@@ -23,7 +23,7 @@ def new_uvbeam(
     feed_version: str = "0.0",
     model_name: str = "default",
     model_version: str = "0.0",
-    feed_array: npt.NDArray[np.str] | None = None,
+    feed_array: npt.NDArray[str] | None = None,
     polarization_array: (
         npt.NDArray[np.str | np.int] | list[str | int] | tuple[str | int] | None
     ) = None,

src/pyuvdata/uvbeam/uvbeam.py

@@ -22,29 +22,6 @@
 __all__ = ["UVBeam"]
 
 
-def _convert_feeds_to_pols(feed_array, calc_cross_pols, x_orientation=None):
-    n_feeds = np.asarray(feed_array).size
-
-    feed_pol_order = [(0, 0)]
-    if n_feeds > 1:
-        feed_pol_order.append((1, 1))
-
-    if calc_cross_pols:
-        # to get here we have Nfeeds > 1
-        feed_pol_order.extend([(0, 1), (1, 0)])
-
-    pol_strings = []
-    for pair in feed_pol_order:
-        pol_strings.append(feed_array[pair[0]] + feed_array[pair[1]])
-    polarization_array = np.array(
-        [
-            utils.polstr2num(ps.upper(), x_orientation=x_orientation)
-            for ps in pol_strings
-        ]
-    )
-    return polarization_array, feed_pol_order
-
-
 class UVBeam(UVBase):
     """
     A class for defining a radio telescope antenna beam.
@@ -927,10 +904,11 @@ def efield_to_power(
             # There are no cross pols with one feed. Set this so the power beam is real
             calc_cross_pols = False
 
-        beam_object.polarization_array, feed_pol_order = _convert_feeds_to_pols(
+        beam_object.polarization_array, feed_pol_order = utils.convert_feeds_to_pols(
             beam_object.feed_array,
-            calc_cross_pols,
+            include_cross_pols=calc_cross_pols,
             x_orientation=beam_object.x_orientation,
+            return_feed_pol_order=True,
         )
         beam_object.Npols = beam_object.polarization_array.size