Clean up code slightly

flacinfo.py

@@ -27,14 +27,20 @@ VORBIS_ARG_NAME = {
 
 
 class NoSuchTag(Exception):
+    """Raised when trying to reverse the `VORBIS_ARG_NAME` dict on an invalid tag name"""
+
     def __init__(self, tag):
+        super().__init__()
         self.tag = tag
-        super(NoSuchTag, self).__init__()
 
     def __str__(self):
         return "No such Vorbis tag {}".format(self.tag)
 
 
+class MetaflacError(Exception):
+    """ Raised when an invocation of metaflac failed. """
+
+
 def argparser():
     """ Parses the arguments from sys.argv """
     parser = argparse.ArgumentParser(
@@ -63,12 +69,14 @@ def is_flac_file(path):
     """ Checks whether `path` refers to an existing, writeable flac file """
     if not os.path.isfile(path) or not os.access(path, os.W_OK):
         return False
-    flac_run = subprocess.run(
+    try:
+        subprocess.run(
             ["metaflac", "--list", path],
             stdout=subprocess.DEVNULL,
             stderr=subprocess.DEVNULL,
+            check=True,
         )
-    if flac_run.returncode != 0:
+    except subprocess.CalledProcessError:
         return False  # Metaflac failed to list the files' metadata
 
     return True
@@ -94,18 +102,14 @@ def edit_flac(args):
     metaflac_args = make_metaflac_args(args)
     metaflac_args += args["file"]
     metaflac_args.insert(0, "metaflac")
-    metaflac_run = subprocess.run(metaflac_args)
-
-    if metaflac_run.returncode != 0:
-        print(
-            (
-                "\n\nMetaflac exited with return code {}. There was an error "
-                "during the execution, you should look at the output to "
-                "investigate it."
-            ).format(metaflac_run.returncode),
-            file=sys.stderr,
+    try:
+        subprocess.run(metaflac_args, check=True)
+    except subprocess.CalledProcessError as exn:
+        raise MetaflacError(
+            "Failed to edit tags: metaflac exited with error {}. Output:\n{}".format(
+                exn.returncode, exn.stderr
             )
-        sys.exit(metaflac_run.returncode)
+        ) from exn
 
 
 def reverse_tag(vorbis_tag):
@@ -123,7 +127,15 @@ def get_tags(path):
         metaflac_args += ["--show-tag", VORBIS_ARG_NAME[tag]]
     metaflac_args.append(path)
 
-    metaflac_run = subprocess.run(metaflac_args, stdout=subprocess.PIPE)
+    try:
+        metaflac_run = subprocess.run(metaflac_args, check=True, stdout=subprocess.PIPE)
+    except subprocess.CalledProcessError as exn:
+        raise MetaflacError(
+            (
+                "Failed to get tags for {}: metaflac exited with error {}."
+                "Output:\n{}"
+            ).format(path, exn.returncode, exn.stderr)
+        ) from exn
     meta_out = metaflac_run.stdout.decode("utf-8")
     output = {}
 
@@ -142,13 +154,14 @@ def show_tags(path):
     tags = get_tags(path)
     print("File: {}".format(path))
 
-    max_len = max([len(tag) for tag in tags])
+    tag_len = max([len(tag) for tag in tags]) + 1
     for tag in tags:
-        print(" {}: {}{}".format(tag, " " * (max_len - len(tag)), tags[tag]))
+        print((" {:<" + str(tag_len) + "} {}").format(tag + ":", tags[tag]))
     print("")
 
 
 def main():
+    """ Entrypoint function """
     args = vars(argparser())
 
     has_errors = False