gh-40456: __iter__ method for the AffineGroup class
    
Fixes #40412.

If it is possible to iterate over a vector space and the corresponding
general linear group, then it should also be possible to iterate over
the associated affine group.  So we add an `__iter__` method to the
`AffineGroup` class (and also a `__len__` method).

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URL: #40456
Reported by: DaveWitteMorris
Reviewer(s):

Author: Release Manager

src/sage/groups/affine_gps/affine_group.py

@@ -532,3 +532,17 @@ def some_elements(self):
         vecs = self.vector_space().some_elements()
         return [self.element_class(self, A, b, check=False, convert=False)
                 for A in mats for b in vecs]
+
+    def __iter__(self):
+        """
+        TESTS::
+
+            sage: G = AffineGroup(2, 3)
+            sage: len([g for g in G]) == G.cardinality()  # indirect doctest
+            True
+        """
+        for A in self._GL:
+            for b in self.vector_space():
+                yield self.element_class(self, A, b, check=False, convert=False)
+
+    __len__ = cardinality