Simplify logic for choosing get_win_folder’s value

Before this change, `windows.py` had multiple different `import ctypes`
and `import winreg` lines. `windows.py` did this for a specific reason.
The `get_win_folder_via_ctypes()` function depends on the `ctypes`
module, and the `get_win_folder_from_registry()` functions depends on
the `winreg` modules, but `windows.py` as a whole is supposed to
continue to work even if `ctypes` and `winreg` are not available.

Before this change, `windows.py` would try to avoid errors by only
calling either of those two functions if the module that that function
requires is not available. This meant that there had to be two
`import ctypes` lines and two `import winreg` lines. The first one would
be inside the body of the function that that depends on the module, and
the second one would be in a test that determines if the function should
be called. The idea was to only call `get_win_folder_via_ctypes()` and
`get_win_folder_from_registry()` if their respective modules are
available.

This change simplifies `windows.py`. Previously, those two functions
were always defined but not always called. Now, those two fuctions are
not always defined and not always called. This means that there’s now
only one `import ctypes` line and only one `import winreg` line. As an
added bonus, those two `import` statements are now at the top of the
file (like the rest of the `import` statements) and the
`_pick_get_win_folder()` function is now simpler.

The main motivation behind this change is to make it easier to create a
future change. That future change will add additional code to
`windows.py` that depends on the `ctypes` module. This change will allow
me to add that additional code without adding an additional
`import ctypes` line.

Author: Jayman2000

src/platformdirs/windows.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import contextlib
 import os
 import sys
 from functools import lru_cache
@@ -12,6 +13,11 @@
 if TYPE_CHECKING:
     from collections.abc import Callable
 
+with contextlib.suppress(ImportError):
+    import ctypes
+with contextlib.suppress(ImportError):
+    import winreg
+
 
 class Windows(PlatformDirsABC):
     """
@@ -180,89 +186,83 @@ def get_win_folder_if_csidl_name_not_env_var(csidl_name: str) -> str | None:
     return None
 
 
-def get_win_folder_from_registry(csidl_name: str) -> str:
-    """
-    Get folder from the registry.
-
-    This is a fallback technique at best. I'm not sure if using the registry for these guarantees us the correct answer
-    for all CSIDL_* names.
+if "winreg" in globals():
 
-    """
-    shell_folder_name = {
-        "CSIDL_APPDATA": "AppData",
-        "CSIDL_COMMON_APPDATA": "Common AppData",
-        "CSIDL_LOCAL_APPDATA": "Local AppData",
-        "CSIDL_PERSONAL": "Personal",
-        "CSIDL_DOWNLOADS": "{374DE290-123F-4565-9164-39C4925E467B}",
-        "CSIDL_MYPICTURES": "My Pictures",
-        "CSIDL_MYVIDEO": "My Video",
-        "CSIDL_MYMUSIC": "My Music",
-    }.get(csidl_name)
-    if shell_folder_name is None:
-        msg = f"Unknown CSIDL name: {csidl_name}"
-        raise ValueError(msg)
-    if sys.platform != "win32":  # only needed for mypy type checker to know that this code runs only on Windows
-        raise NotImplementedError
-    import winreg  # noqa: PLC0415
-
-    key = winreg.OpenKey(winreg.HKEY_CURRENT_USER, r"Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders")
-    directory, _ = winreg.QueryValueEx(key, shell_folder_name)
-    return str(directory)
-
-
-def get_win_folder_via_ctypes(csidl_name: str) -> str:
-    """Get folder with ctypes."""
-    # There is no 'CSIDL_DOWNLOADS'.
-    # Use 'CSIDL_PROFILE' (40) and append the default folder 'Downloads' instead.
-    # https://learn.microsoft.com/en-us/windows/win32/shell/knownfolderid
-
-    import ctypes  # noqa: PLC0415
-
-    csidl_const = {
-        "CSIDL_APPDATA": 26,
-        "CSIDL_COMMON_APPDATA": 35,
-        "CSIDL_LOCAL_APPDATA": 28,
-        "CSIDL_PERSONAL": 5,
-        "CSIDL_MYPICTURES": 39,
-        "CSIDL_MYVIDEO": 14,
-        "CSIDL_MYMUSIC": 13,
-        "CSIDL_DOWNLOADS": 40,
-        "CSIDL_DESKTOPDIRECTORY": 16,
-    }.get(csidl_name)
-    if csidl_const is None:
-        msg = f"Unknown CSIDL name: {csidl_name}"
-        raise ValueError(msg)
-
-    buf = ctypes.create_unicode_buffer(1024)
-    windll = getattr(ctypes, "windll")  # noqa: B009 # using getattr to avoid false positive with mypy type checker
-    windll.shell32.SHGetFolderPathW(None, csidl_const, None, 0, buf)
-
-    # Downgrade to short path name if it has high-bit chars.
-    if any(ord(c) > 255 for c in buf):  # noqa: PLR2004
-        buf2 = ctypes.create_unicode_buffer(1024)
-        if windll.kernel32.GetShortPathNameW(buf.value, buf2, 1024):
-            buf = buf2
+    def get_win_folder_from_registry(csidl_name: str) -> str:
+        """
+        Get folder from the registry.
 
-    if csidl_name == "CSIDL_DOWNLOADS":
-        return os.path.join(buf.value, "Downloads")  # noqa: PTH118
+        This is a fallback technique at best. I'm not sure if using the registry for these guarantees us the correct
+        answer for all CSIDL_* names.
 
-    return buf.value
+        """
+        shell_folder_name = {
+            "CSIDL_APPDATA": "AppData",
+            "CSIDL_COMMON_APPDATA": "Common AppData",
+            "CSIDL_LOCAL_APPDATA": "Local AppData",
+            "CSIDL_PERSONAL": "Personal",
+            "CSIDL_DOWNLOADS": "{374DE290-123F-4565-9164-39C4925E467B}",
+            "CSIDL_MYPICTURES": "My Pictures",
+            "CSIDL_MYVIDEO": "My Video",
+            "CSIDL_MYMUSIC": "My Music",
+        }.get(csidl_name)
+        if shell_folder_name is None:
+            msg = f"Unknown CSIDL name: {csidl_name}"
+            raise ValueError(msg)
+        if sys.platform != "win32":  # only needed for mypy type checker to know that this code runs only on Windows
+            raise NotImplementedError
+
+        key = winreg.OpenKey(
+            winreg.HKEY_CURRENT_USER, r"Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders"
+        )
+        directory, _ = winreg.QueryValueEx(key, shell_folder_name)
+        return str(directory)
+
+
+if "ctypes" in globals() and hasattr(ctypes, "windll"):
+
+    def get_win_folder_via_ctypes(csidl_name: str) -> str:
+        """Get folder with ctypes."""
+        # There is no 'CSIDL_DOWNLOADS'.
+        # Use 'CSIDL_PROFILE' (40) and append the default folder 'Downloads' instead.
+        # https://learn.microsoft.com/en-us/windows/win32/shell/knownfolderid
+        csidl_const = {
+            "CSIDL_APPDATA": 26,
+            "CSIDL_COMMON_APPDATA": 35,
+            "CSIDL_LOCAL_APPDATA": 28,
+            "CSIDL_PERSONAL": 5,
+            "CSIDL_MYPICTURES": 39,
+            "CSIDL_MYVIDEO": 14,
+            "CSIDL_MYMUSIC": 13,
+            "CSIDL_DOWNLOADS": 40,
+            "CSIDL_DESKTOPDIRECTORY": 16,
+        }.get(csidl_name)
+        if csidl_const is None:
+            msg = f"Unknown CSIDL name: {csidl_name}"
+            raise ValueError(msg)
+
+        buf = ctypes.create_unicode_buffer(1024)
+        windll = getattr(ctypes, "windll")  # noqa: B009 # using getattr to avoid false positive with mypy type checker
+        windll.shell32.SHGetFolderPathW(None, csidl_const, None, 0, buf)
+
+        # Downgrade to short path name if it has high-bit chars.
+        if any(ord(c) > 255 for c in buf):  # noqa: PLR2004
+            buf2 = ctypes.create_unicode_buffer(1024)
+            if windll.kernel32.GetShortPathNameW(buf.value, buf2, 1024):
+                buf = buf2
+
+        if csidl_name == "CSIDL_DOWNLOADS":
+            return os.path.join(buf.value, "Downloads")  # noqa: PTH118
+
+        return buf.value
 
 
 def _pick_get_win_folder() -> Callable[[str], str]:
-    try:
-        import ctypes  # noqa: PLC0415
-    except ImportError:
-        pass
-    else:
-        if hasattr(ctypes, "windll"):
-            return get_win_folder_via_ctypes
-    try:
-        import winreg  # noqa: PLC0415, F401
-    except ImportError:
-        return get_win_folder_from_env_vars
-    else:
+    if "get_win_folder_via_ctypes" in globals():
+        return get_win_folder_via_ctypes
+    if "get_win_folder_from_registry" in globals():
         return get_win_folder_from_registry
+    return get_win_folder_from_env_vars
 
 
 get_win_folder = lru_cache(maxsize=None)(_pick_get_win_folder())