Fix mypy errors on master branch (materialsproject#3977)

* improve type and simplify iterative_symmetrize

* fix type error and tweak types for compatibility

* fix packmol type

* fix type for site_transformation

* ignore type override

* fix type for species

* docstring tweak

* since it says preprocess in comment above, prob not meant to return here

---------

Co-authored-by: Janosh Riebesell <[email protected]>

Author: DanielYang59

src/pymatgen/analysis/structure_prediction/substitution_probability.py

@@ -76,7 +76,7 @@ def __init__(self, lambda_table=None, alpha=-5):
 
         # create Z and px
         self.Z = 0
-        self._px: dict[Species, float] = defaultdict(float)
+        self._px: dict[SpeciesLike, float] = defaultdict(float)
         for s1, s2 in itertools.product(self.species, repeat=2):
             value = math.exp(self.get_lambda(s1, s2))
             self._px[s1] += value / 2

src/pymatgen/core/periodic_table.py

@@ -12,7 +12,7 @@
 from enum import Enum, unique
 from itertools import combinations, product
 from pathlib import Path
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, overload
 
 import numpy as np
 from monty.dev import deprecated
@@ -1597,11 +1597,21 @@ class DummySpecie(DummySpecies):
     """
 
 
+@overload
+def get_el_sp(obj: int) -> Element:
+    pass
+
+
+@overload
+def get_el_sp(obj: SpeciesLike) -> Element | Species | DummySpecies:
+    pass
+
+
 @functools.lru_cache
 def get_el_sp(obj: int | SpeciesLike) -> Element | Species | DummySpecies:
-    """Utility method to get an Element, Species or DummySpecies from any input.
+    """Utility function to get an Element, Species or DummySpecies from any input.
 
-    If obj is in itself an element or a specie, it is returned automatically.
+    If obj is an Element or a Species, it is returned as is.
     If obj is an int or a string representing an integer, the Element with the
     atomic number obj is returned.
     If obj is a string, Species parsing will be attempted (e.g. Mn2+). Failing that
@@ -1616,8 +1626,8 @@ def get_el_sp(obj: int | SpeciesLike) -> Element | Species | DummySpecies:
         ValueError: if obj cannot be converted into an Element or Species.
 
     Returns:
-        Species | Element: with a bias for the maximum number of properties
-            that can be determined.
+        Element | Species | DummySpecies: with a bias for the maximum number
+            of properties that can be determined.
     """
     # If obj is already an Element or Species, return as is
     if isinstance(obj, (Element, Species, DummySpecies)):