[3.14] gh-95844: Move help_url code to a help module function (GH-129971) (#138484)

gh-95844: Move help_url code to a help module function (GH-129971)

---------
(cherry picked from commit 3b4cd88563)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>

Lib/idlelib/help.py

@@ -23,7 +23,12 @@
 copy_strip - Copy the text part of idle.html to help.html while rstripping each line.
 
 show_idlehelp - Create HelpWindow.  Called in EditorWindow.help_dialog.
+
+_get_dochome() - Return path to docs on user's system if present,
+otherwise return link to docs.python.org.
 """
+import os
+import sys
 from html.parser import HTMLParser
 from os.path import abspath, dirname, isfile, join
 from platform import python_version
@@ -289,6 +294,47 @@ def show_idlehelp(parent):
     return HelpWindow(parent, filename, 'IDLE Doc (%s)' % python_version())
 
 
+def _get_dochome():
+    "Return path to local docs if present, otherwise link to docs.python.org."
+
+    dochome = os.path.join(sys.base_prefix, 'Doc', 'index.html')
+    if sys.platform.count('linux'):
+        # look for html docs in a couple of standard places
+        pyver = 'python-docs-' + '%s.%s.%s' % sys.version_info[:3]
+        if os.path.isdir('/var/www/html/python/'):  # rpm package manager
+            dochome = '/var/www/html/python/index.html'
+        else:
+            basepath = '/usr/share/doc/'  # dnf/apt package managers
+            dochome = os.path.join(basepath, pyver, 'Doc', 'index.html')
+
+    elif sys.platform[:3] == 'win':
+        import winreg  # Windows only, block only executed once.
+        docfile = ''
+        KEY = (rf"Software\Python\PythonCore\{sys.winver}"
+               r"\Help\Main Python Documentation")
+        try:
+            docfile = winreg.QueryValue(winreg.HKEY_CURRENT_USER, KEY)
+        except FileNotFoundError:
+            try:
+                docfile = winreg.QueryValue(winreg.HKEY_LOCAL_MACHINE, KEY)
+            except FileNotFoundError:
+                pass
+        if os.path.isfile(docfile):
+            dochome = docfile
+    elif sys.platform == 'darwin':
+        # documentation may be stored inside a python framework
+        dochome = os.path.join(sys.base_prefix,
+                               'Resources/English.lproj/Documentation/index.html')
+    dochome = os.path.normpath(dochome)
+    if os.path.isfile(dochome):
+        if sys.platform == 'darwin':
+            # Safari requires real file:-URLs
+            return 'file://' + dochome
+        return dochome
+    else:
+        return "https://docs.python.org/%d.%d/" % sys.version_info[:2]
+
+
 if __name__ == '__main__':
     from unittest import main
     main('idlelib.idle_test.test_help', verbosity=2, exit=False)