standardise program/sox.py formatting, add test case, docstring (#53)

* standardise program/sox.py formatting, add test case
* add program/sox.peak_level() docstring
* update .travis.yml to include sox as a test dependency
* move sox from test dependency to normal dependency
* update README to mention sox, remove small autoconf mention
* use .splitlines() instead of .split('n')

morituri/program/sox.py

@@ -1,16 +1,24 @@
-import os
 import logging
+import os
 from subprocess import Popen, PIPE
 
 SOX = 'sox'
 
 def peak_level(track_path):
-	if not os.path.exists(track_path):
-		logging.warning("SoX peak detection failed: file not found")
-		return None
-	sox = Popen([SOX, track_path, "-n", "stat"], stderr=PIPE)
-	out, err = sox.communicate()
-	if sox.returncode:
-		logging.warning("SoX peak detection failed: " + s.returncode)
-		return None
-	return float(err.split('\n')[3].split()[2])	# Maximum amplitude: 0.123456
+    """
+    Accepts a path to a sox-decodable audio file.
+
+    Returns track peak level from sox ('maximum amplitude') as a float.
+    Returns None on error.
+    """
+    if not os.path.exists(track_path):
+        logging.warning("SoX peak detection failed: file not found")
+        return None
+    sox = Popen([SOX, track_path, "-n", "stat"], stderr=PIPE)
+    out, err = sox.communicate()
+    if sox.returncode:
+        logging.warning("SoX peak detection failed: " + str(sox.returncode))
+        return None
+    # relevant captured line looks like:
+    # Maximum amplitude: 0.123456
+    return float(err.splitlines()[3].split()[2])