refactor(sources): use EAFP pattern instead of is_file() check

Replace the is_file() stat syscall with a try/except around open() to
handle symlinks to directories in scan_compiled_extensions. This avoids
an extra syscall per file, eliminates the TOCTOU race between the check
and the open, and is more idiomatic Python (EAFP over LBYL).

Only IsADirectoryError is caught to avoid masking real I/O errors.

Co-Authored-By: Claude Opus 4.6 <claude@anthropic.com>
Signed-off-by: Mike DePaulo <mikedep333@redhat.com>

Author: 2 people

src/fromager/sources.py

@@ -867,10 +867,11 @@ def scan_compiled_extensions(
             elif suffix not in ignore_suffixes:
                 # Path.walk() lists symlinks to directories as filenames
                 # rather than dirnames, causing IsADirectoryError on open().
-                if not filepath.is_file():
+                try:
+                    with filepath.open("rb") as f:
+                        header = f.read(_MAGIC_HEADERS_READ)
+                except IsADirectoryError:
                     continue
-                with filepath.open("rb") as f:
-                    header = f.read(_MAGIC_HEADERS_READ)
                 if header.startswith(magic_headers):
                     relpath = filepath.relative_to(root_dir)
                     logger.debug(