gh-39989: Refactor imports in PoorManMap and Sequence classes
    
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Minor refactoring to prefer importing the object (`from
sage.structure.sage_object import SageObject`) over the module (`import
sage.structure.sage_object`).

Part of making all sage modules import without `sage.all`.


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### ⌛ Dependencies

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URL: #39989
Reported by: Tobias Diez
Reviewer(s): Frédéric Chapoton

Author: Release Manager

src/sage/categories/poor_man_map.py

@@ -12,10 +12,10 @@
 # (at your option) any later version.
 #                  https://www.gnu.org/licenses/
 # ****************************************************************************
-import sage.structure.sage_object
+from sage.structure.sage_object import SageObject
 
 
-class PoorManMap(sage.structure.sage_object.SageObject):
+class PoorManMap(SageObject):
     """
     A class for maps between sets which are not (yet) modeled by parents.
 
@@ -264,7 +264,7 @@ def _sympy_(self):
             sage: h._sympy_()                                                           # needs sympy sage.symbolic
             sin
         """
-        from sympy import Lambda, sympify
+        from sympy import sympify
         if len(self._functions) == 1:
             return sympify(self._functions[0])
         raise NotImplementedError

src/sage/structure/sequence.py

@@ -71,8 +71,7 @@
 # ****************************************************************************
 
 from sage.misc.persist import register_unpickle_override
-import sage.structure.sage_object
-import sage.structure.coerce
+from sage.structure.sage_object import SageObject
 
 
 def Sequence(x, universe=None, check=True, immutable=False, cr=False, cr_str=None, use_sage_types=False):
@@ -259,7 +258,9 @@ def Sequence(x, universe=None, check=True, immutable=False, cr=False, cr_str=Non
             x = list(x)
         else:
             try:
-                from sage.rings.polynomial.multi_polynomial_ideal import MPolynomialIdeal
+                from sage.rings.polynomial.multi_polynomial_ideal import (
+                    MPolynomialIdeal,
+                )
             except ImportError:
                 pass
             else:
@@ -293,9 +294,9 @@ def Sequence(x, universe=None, check=True, immutable=False, cr=False, cr_str=Non
                 universe = sage.structure.element.parent(x[len(x)-1])
 
     try:
+        from sage.rings.polynomial.multi_polynomial_ring import MPolynomialRing_base
         from sage.rings.polynomial.multi_polynomial_sequence import PolynomialSequence
         from sage.rings.polynomial.pbori.pbori import BooleanMonomialMonoid
-        from sage.rings.polynomial.multi_polynomial_ring import MPolynomialRing_base
         from sage.rings.quotient_ring import QuotientRing_nc
     except ImportError:
         pass
@@ -306,7 +307,7 @@ def Sequence(x, universe=None, check=True, immutable=False, cr=False, cr_str=Non
     return Sequence_generic(x, universe, check, immutable, cr, cr_str, use_sage_types)
 
 
-class Sequence_generic(sage.structure.sage_object.SageObject, list):
+class Sequence_generic(SageObject, list):
     """
     A mutable list of elements with a common guaranteed universe,
     which can be set immutable.