gh-38465: using pathlib.Path around SAGE_EXTCODE

    
replacing `os` by the much lighter `pathlib` library in some places

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
    
URL: #38465
Reported by: Frédéric Chapoton
Reviewer(s): Kwankyu Lee

src/sage/features/threejs.py

@@ -1,5 +1,5 @@
 # sage_setup: distribution = sagemath-environment
-import os
+from pathlib import Path
 
 from . import StaticFile
 
@@ -26,16 +26,17 @@ def __init__(self):
         """
         from sage.env import SAGE_SHARE, THREEJS_DIR
 
+        share_dir = Path(SAGE_SHARE)
         threejs_search_path = THREEJS_DIR or (
-            os.path.join(SAGE_SHARE, "jupyter", "nbextensions", "threejs-sage"),
-            os.path.join(SAGE_SHARE, "sagemath", "threejs-sage"),
-            os.path.join(SAGE_SHARE, "sage", "threejs"),
-            os.path.join(SAGE_SHARE, "threejs-sage")
+            (share_dir / "jupyter" / "nbextensions" / "threejs-sage"),
+            (share_dir / "sagemath" / "threejs-sage"),
+            (share_dir / "sage" / "threejs"),
+            (share_dir / "threejs-sage")
             )
 
         try:
             version = self.required_version()
-            filename = os.path.join(version, "three.min.js")
+            filename = Path(version) / "three.min.js"
         except FileNotFoundError:
             filename = 'unknown'
 
@@ -64,7 +65,7 @@ def required_version(self):
         """
         from sage.env import SAGE_EXTCODE
 
-        filename = os.path.join(SAGE_EXTCODE, 'threejs', 'threejs-version.txt')
+        filename = Path(SAGE_EXTCODE) / 'threejs' / 'threejs-version.txt'
 
         with open(filename) as f:
             return f.read().strip()

src/sage/graphs/graph_plot_js.py

@@ -73,9 +73,9 @@
 Functions
 ---------
 """
+from pathlib import Path
 from sage.misc.temporary_file import tmp_filename
 from sage.misc.lazy_import import lazy_import
-import os
 lazy_import("sage.plot.colors", "rainbow")
 
 # ****************************************************************************
@@ -317,13 +317,12 @@ def gen_html_code(G,
                                    "edge_thickness": int(edge_thickness)})
 
     from sage.env import SAGE_EXTCODE, SAGE_SHARE
-    js_code_file = open(SAGE_EXTCODE + "/graphs/graph_plot_js.html", 'r')
-    js_code = js_code_file.read().replace("// GRAPH_DATA_HEREEEEEEEEEEE", string)
-    js_code_file.close()
+    with open(Path(SAGE_EXTCODE) / "graphs" / "graph_plot_js.html", 'r') as f:
+        js_code = f.read().replace("// GRAPH_DATA_HEREEEEEEEEEEE", string)
 
     # Add d3.js script depending on whether d3js package is installed.
-    d3js_filepath = os.path.join(SAGE_SHARE, 'd3js', 'd3.min.js')
-    if os.path.exists(d3js_filepath):
+    d3js_filepath = Path(SAGE_SHARE) / 'd3js' / 'd3.min.js'
+    if d3js_filepath.exists():
         with open(d3js_filepath, 'r') as d3js_code_file:
             d3js_script = '<script>' + d3js_code_file.read() + '</script>'
     else:

src/sage/groups/perm_gps/permgroup_named.py

@@ -2794,8 +2794,8 @@ def ramification_module_decomposition_hurwitz_curve(self):
 
         F = self.base_ring()
         q = F.order()
-        libgap.Read(str(Path(SAGE_EXTCODE) / 'gap' / 'joyner' /
-                        'hurwitz_crv_rr_sp.gap'))
+        libgap.Read(Path(SAGE_EXTCODE) / 'gap' / 'joyner' /
+                    'hurwitz_crv_rr_sp.gap')
         mults = libgap.eval(f"ram_module_hurwitz({q})")
         return mults.sage()
 
@@ -2838,8 +2838,8 @@ def ramification_module_decomposition_modular_curve(self):
             raise ValueError("degree must be 2")
         F = self.base_ring()
         q = F.order()
-        libgap.Read(str(Path(SAGE_EXTCODE) / 'gap' / 'joyner' /
-                        'modular_crv_rr_sp.gap'))
+        libgap.Read(Path(SAGE_EXTCODE) / 'gap' / 'joyner' /
+                    'modular_crv_rr_sp.gap')
         mults = libgap.eval(f"ram_module_X({q})")
         return mults.sage()