diff --git a/wifimon.py b/wifimon.py
index 6f2d1ce..3565462 100755
--- a/wifimon.py
+++ b/wifimon.py
@@ -1,30 +1,41 @@
 #!/usr/bin/env python2
+"""Functions for decoding wifi pcap files."""
 
 from __future__ import print_function
-import gzip
 import bz2
 import csv
-import os
-import string
+import gzip
 import struct
-import subprocess
 import sys
 
+
 class Struct(dict):
-    def __init__(self, *args, **kwargs):
-        dict.__init__(self, *args, **kwargs)
-        self.__dict__.update(**kwargs)
-    def __getattr__(self, name):
-        return self[name]
-    def __setattr__(self, name, value):
-        self[name] = value
-    def __delattr__(self, name):
-        del self[name]
+  """Helper to allow accessing dict members using this.that notation."""
+
+  def __init__(self, *args, **kwargs):
+    dict.__init__(self, *args, **kwargs)
+    self.__dict__.update(**kwargs)
+
+  def __getattr__(self, name):
+    return self[name]
+
+  def __setattr__(self, name, value):
+    self[name] = value
+
+  def __delattr__(self, name):
+    del self[name]
 
 TCPDUMP_MAGIC = 0xa1b2c3d4
 TCPDUMP_VERSION = (2, 4)
 LINKTYPE_IEEE802_11_RADIOTAP = 127
 
+
+class Flags(object):
+  """Flags in the radiotap header."""
+  # TODO(apenwarr): add the other flags here
+  BAD_MCS = 0x40
+
+
 RADIOTAP_FIELDS = [
     ('mac_usecs', 'Q'),
     ('flags', 'B'),
@@ -50,6 +61,7 @@
     ('vht', 'HBB4sBBH'),
 ]
 
+
 _STDFRAME = ('ra', 'ta', 'xa', 'seq')
 DOT11_TYPES = {
     # Management
@@ -106,6 +118,7 @@
 
 
 def HexDump(s):
+  """Convert a binary array to a printable hexdump."""
   out = ''
   for row in xrange(0, len(s), 16):
     out += '%04x ' % row
@@ -132,70 +145,73 @@
 
 
 MCS_TABLE = [
-    (1, "BPSK", "1/2", (6.50, 7.20, 13.50, 15.00)),
-    (1, "QPSK", "1/2", (13.00, 14.40, 27.00, 30.00)),
-    (1, "QPSK", "3/4", (19.50, 21.70, 40.50, 45.00)),
-    (1, "16-QAM", "1/2", (26.00, 28.90, 54.00, 60.00)),
-    (1, "16-QAM", "3/4", (39.00, 43.30, 81.00, 90.00)),
-    (1, "64-QAM", "2/3", (52.00, 57.80, 108.00, 120.00)),
-    (1, "64-QAM", "3/4", (58.50, 65.00, 121.50, 135.00)),
-    (1, "64-QAM", "5/6", (65.00, 72.20, 135.00, 150.00)),
-    (2, "BPSK", "1/2", (13.00, 14.40, 27.00, 30.00)),
-    (2, "QPSK", "1/2", (26.00, 28.90, 54.00, 60.00)),
-    (2, "QPSK", "3/4", (39.00, 43.30, 81.00, 90.00)),
-    (2, "16-QAM", "1/2", (52.00, 57.80, 108.00, 120.00)),
-    (2, "16-QAM", "3/4", (78.00, 86.70, 162.00, 180.00)),
-    (2, "64-QAM", "2/3", (104.00, 115.60, 216.00, 240.00)),
-    (2, "64-QAM", "3/4", (117.00, 130.00, 243.00, 270.00)),
-    (2, "64-QAM", "5/6", (130.00, 144.40, 270.00, 300.00)),
-    (3, "BPSK", "1/2", (19.50, 21.70, 40.50, 45.00)),
-    (3, "QPSK", "1/2", (39.00, 43.30, 81.00, 90.00)),
-    (3, "QPSK", "3/4", (58.50, 65.00, 121.50, 135.00)),
-    (3, "16-QAM", "1/2", (78.00, 86.70, 162.00, 180.00)),
-    (3, "16-QAM", "3/4", (117.00, 130.00, 243.00, 270.00)),
-    (3, "64-QAM", "2/3", (156.00, 173.30, 324.00, 360.00)),
-    (3, "64-QAM", "3/4", (175.50, 195.00, 364.50, 405.00)),
-    (3, "64-QAM", "5/6", (195.00, 216.70, 405.00, 450.00)),
-    (4, "BPSK", "1/2", (26.00, 28.80, 54.00, 60.00)),
-    (4, "QPSK", "1/2", (52.00, 57.60, 108.00, 120.00)),
-    (4, "QPSK", "3/4", (78.00, 86.80, 162.00, 180.00)),
-    (4, "16-QAM", "1/2", (104.00, 115.60, 216.00, 240.00)),
-    (4, "16-QAM", "3/4", (156.00, 173.20, 324.00, 360.00)),
-    (4, "64-QAM", "2/3", (208.00, 231.20, 432.00, 480.00)),
-    (4, "64-QAM", "3/4", (234.00, 260.00, 486.00, 540.00)),
-    (4, "64-QAM", "5/6", (260.00, 288.80, 540.00, 600.00)),
-    (1, "BPSK", "1/2", (0, 0, 6.50, 7.20)),
+    (1, 'BPSK', '1/2', (6.50, 7.20, 13.50, 15.00)),
+    (1, 'QPSK', '1/2', (13.00, 14.40, 27.00, 30.00)),
+    (1, 'QPSK', '3/4', (19.50, 21.70, 40.50, 45.00)),
+    (1, '16-QAM', '1/2', (26.00, 28.90, 54.00, 60.00)),
+    (1, '16-QAM', '3/4', (39.00, 43.30, 81.00, 90.00)),
+    (1, '64-QAM', '2/3', (52.00, 57.80, 108.00, 120.00)),
+    (1, '64-QAM', '3/4', (58.50, 65.00, 121.50, 135.00)),
+    (1, '64-QAM', '5/6', (65.00, 72.20, 135.00, 150.00)),
+    (2, 'BPSK', '1/2', (13.00, 14.40, 27.00, 30.00)),
+    (2, 'QPSK', '1/2', (26.00, 28.90, 54.00, 60.00)),
+    (2, 'QPSK', '3/4', (39.00, 43.30, 81.00, 90.00)),
+    (2, '16-QAM', '1/2', (52.00, 57.80, 108.00, 120.00)),
+    (2, '16-QAM', '3/4', (78.00, 86.70, 162.00, 180.00)),
+    (2, '64-QAM', '2/3', (104.00, 115.60, 216.00, 240.00)),
+    (2, '64-QAM', '3/4', (117.00, 130.00, 243.00, 270.00)),
+    (2, '64-QAM', '5/6', (130.00, 144.40, 270.00, 300.00)),
+    (3, 'BPSK', '1/2', (19.50, 21.70, 40.50, 45.00)),
+    (3, 'QPSK', '1/2', (39.00, 43.30, 81.00, 90.00)),
+    (3, 'QPSK', '3/4', (58.50, 65.00, 121.50, 135.00)),
+    (3, '16-QAM', '1/2', (78.00, 86.70, 162.00, 180.00)),
+    (3, '16-QAM', '3/4', (117.00, 130.00, 243.00, 270.00)),
+    (3, '64-QAM', '2/3', (156.00, 173.30, 324.00, 360.00)),
+    (3, '64-QAM', '3/4', (175.50, 195.00, 364.50, 405.00)),
+    (3, '64-QAM', '5/6', (195.00, 216.70, 405.00, 450.00)),
+    (4, 'BPSK', '1/2', (26.00, 28.80, 54.00, 60.00)),
+    (4, 'QPSK', '1/2', (52.00, 57.60, 108.00, 120.00)),
+    (4, 'QPSK', '3/4', (78.00, 86.80, 162.00, 180.00)),
+    (4, '16-QAM', '1/2', (104.00, 115.60, 216.00, 240.00)),
+    (4, '16-QAM', '3/4', (156.00, 173.20, 324.00, 360.00)),
+    (4, '64-QAM', '2/3', (208.00, 231.20, 432.00, 480.00)),
+    (4, '64-QAM', '3/4', (234.00, 260.00, 486.00, 540.00)),
+    (4, '64-QAM', '5/6', (260.00, 288.80, 540.00, 600.00)),
+    (1, 'BPSK', '1/2', (0, 0, 6.50, 7.20)),
 ]
 
-def mcs2rate(tb):
-#    known=tb[0]
-#    flags=tb[1]
-# ********************************************
-# ************* currently broken code here ***
-# ************ FIXME FIXME FIXME FIXME *******
-# ********************************************
-    if known & (1 << 0):
-        bw=(20,40,20,20)[flags & 0x3]
-    else:
-        bw=20
-    if known & (1 << 2):
-        gi=((flags&0x4) >> 2)
-    else:
-        gi=0
-    if known & (1 << 1):
-        mcs=tb[2]
-    else:
-        mcs=0
-    if bw==20:
-        si=0
-    else:
-        si=2
-    if gi:
-        si += 1
-    return MCS_TABLE[mcs][3][si]
+
+def McsToRate(tb):
+  """Given an MCS (known,flags) tuple, return the corresponding bitrate."""
+  #    known=tb[0]
+  #    flags=tb[1]
+  # ********************************************
+  # ************* currently broken code here ***
+  # ************ FIXME FIXME FIXME FIXME *******
+  # ********************************************
+  if known & (1 << 0):
+    bw = (20, 40, 20, 20)[flags & 0x3]
+  else:
+    bw = 20
+  if known & (1 << 2):
+    gi = ((flags & 0x4) >> 2)
+  else:
+    gi = 0
+  if known & (1 << 1):
+    mcs = tb[2]
+  else:
+    mcs = 0
+  if bw == 20:
+    si = 0
+  else:
+    si = 2
+  if gi:
+    si += 1
+  return MCS_TABLE[mcs][3][si]
 
 
 def Packetize(stream):
+  """Given a file containing pcap data, yield a series of packets."""
   # pcap global header
   magicbytes = stream.read(4)
   if struct.unpack('<I', magicbytes) == (TCPDUMP_MAGIC,):
@@ -238,7 +254,6 @@
     opt.incl_len = incl_len
     opt.orig_len = orig_len
 
-
     # radiotap header (always little-endian)
     (it_version, unused_it_pad,
      it_len, it_present) = struct.unpack('<BBHI', radiotap[:8])
@@ -252,7 +267,7 @@
       if it_present & (1 << i):
         ofs = Align(ofs, struct.calcsize(format[0]))
         sz = struct.calcsize(format)
-        v = struct.unpack(format, optbytes[ofs:ofs+sz])
+        v = struct.unpack(format, optbytes[ofs:ofs + sz])
         if name == 'mac_usecs':
           opt.mac_usecs = v[0]
           # opt.mac_secs = v[0] / 1e6
@@ -290,46 +305,46 @@
     ofs = 4
     for i, fieldname in enumerate(typefields):
       if fieldname == 'seq':
-        seq = struct.unpack('<H', frame[ofs:ofs+2])[0]
+        seq = struct.unpack('<H', frame[ofs:ofs + 2])[0]
         opt.seq = (seq & 0xfff0) >> 4
         opt.frag = (seq & 0x000f)
         ofs += 2
       else:
-        opt[fieldname] = MacAddr(frame[ofs:ofs+6])
+        opt[fieldname] = MacAddr(frame[ofs:ofs + 6])
         ofs += 6
-    
+
     yield opt, frame
 
 
-def d(p):
-  basetime=0
+def Example(p):
   if 0:
+    basetime = 0
     for opt, frame in Packetize(p):
-        ts=opt.pcap_secs
-        if basetime:
-            ts -= basetime
-        else:
-            basetime=ts
-            ts=0
-        print (ts, opt)
+      ts = opt.pcap_secs
+      if basetime:
+        ts -= basetime
+      else:
+        basetime = ts
+        ts = 0
+      print (ts, opt)
 #      print HexDump(frame)
   elif 1:
     want_fields = [
         'ta',
         'ra',
-#        'xa',
-#        'freq',
+        #        'xa',
+        #        'freq',
         'seq',
         'mcs',
         'rate',
         'retry',
         'dbm_antsignal',
         'dbm_antnoise',
-#        'frag',
+        #        'frag',
         'typestr',
-#        'powerman',
-#        'order',
-#        'dsmode',
+        #        'powerman',
+        #        'order',
+        #        'dsmode',
     ]
     co = csv.writer(sys.stdout)
     co.writerow(['pcap_secs'] + want_fields)
@@ -340,49 +355,42 @@
       if not tbase_pcap: tbase_pcap = t_pcap
       co.writerow(['%.6f' % (t_pcap - tbase_pcap)] +
                   [opt.get(f, None) for f in want_fields])
-#      sys.stdout.flush()
   else:
-      try:
-          for opt, frame in Packetize(p):
-              ts=opt.pcap_secs
-#              if basetime:
-#                  ts -= basetime
-#              else:
-#                  basetime=ts
-#                  ts=0
-              ts="%.09f"%ts
-              if 'xa' in opt:
-                  src=opt.xa
-              else:
-                  src='no:xa:00:00:00:00'
-              if 'mac_usecs' in opt:
-#                  if opt.mac_usecs > 4294967296:
-#                      continue
-                  mac_usecs = opt.mac_usecs
-              else:
-                  mac_usecs = 0
-              if 'seq' in opt:
-                  seq = opt.seq
-              else:
-                  seq = 'noseq'
-              if 'flags' in opt:
-                  if opt.flags & 0x40:    # "Bad FCS" flag in radiotap header
-                      continue
-              if 'mcs' in opt:
-                  print (src, opt.dsmode, opt.typestr, ts, mcs2rate(opt.mcs), mac_usecs, opt.orig_len, seq, opt.flags)
-              else:
-                  print (src, opt.dsmode, opt.typestr, ts, opt.rate, mac_usecs, opt.orig_len, seq, opt.flags)
+    for opt, frame in Packetize(p):
+      ts = opt.pcap_secs
+      ts = '%.09f' % ts
+      if 'xa' in opt:
+        src = opt.xa
+      else:
+        src = 'no:xa:00:00:00:00'
+      if 'mac_usecs' in opt:
+        mac_usecs = opt.mac_usecs
+      else:
+        mac_usecs = 0
+      if 'seq' in opt:
+        seq = opt.seq
+      else:
+        seq = 'noseq'
+      if 'flags' in opt:
+        if opt.flags & Flags.BAD_FCS:
+          continue
+      if 'mcs' in opt:
+        print(
+            src, opt.dsmode, opt.typestr, ts, McsToRate(opt.mcs), mac_usecs,
+            opt.orig_len, seq, opt.flags)
+      else:
+        print(
+            src, opt.dsmode, opt.typestr, ts, opt.rate, mac_usecs,
+            opt.orig_len, seq, opt.flags)
 
-      finally:
-          pass
 
-def zopen(fn):
-    if fn.endswith(".bz2"):
-        return bz2.BZ2File(fn)
-    if fn.endswith(".gz"):
-        return gzip.open(fn)
-    return open(fn)
+def ZOpen(fn):
+  if fn.endswith('.bz2'):
+    return bz2.BZ2File(fn)
+  if fn.endswith('.gz'):
+    return gzip.open(fn)
+  return open(fn)
+
 
 if __name__ == '__main__':
-    p=zopen(sys.argv[1])
-    d(p)
+  Example(ZOpen(sys.argv[1]))