From 4fe144d274308e8794ed8c363a9a5904e6b5e27a Mon Sep 17 00:00:00 2001
From: Andrew Stanton <Refefer@gmail.com>
Date: Thu, 6 Jun 2013 19:28:40 -0400
Subject: [PATCH] Adds a couple of useful options such as adjusting poll time
 with execute time

---
 tail.py | 49 ++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 13 deletions(-)

diff --git a/tail.py b/tail.py
index c9e4fc2..c16eddd 100644
--- a/tail.py
+++ b/tail.py
@@ -25,10 +25,11 @@
 import os
 import sys
 import time
+from cStringIO import StringIO
 
 class Tail(object):
     ''' Represents a tail command. '''
-    def __init__(self, tailed_file):
+    def __init__(self, tailed_file, max_line_length=float("inf")):
         ''' Initiate a Tail instance.
             Check for file validity, assigns callback function to standard out.
             
@@ -38,25 +39,38 @@ def __init__(self, tailed_file):
         self.check_file_validity(tailed_file)
         self.tailed_file = tailed_file
         self.callback = sys.stdout.write
+        self.max_line_length=max_line_length
 
-    def follow(self, s=1):
+    def follow(self, s=1, poll_time=.01):
         ''' Do a tail follow. If a callback function is registered it is called with every new line. 
         Else printed to standard out.
     
         Arguments:
             s - Number of seconds to wait between each iteration; Defaults to 1. '''
-
-        with open(self.tailed_file) as file_:
-            # Go to the end of file
-            file_.seek(0,2)
+        readBuffer = StringIO()
+        with open(self.tailed_file, 'rb') as file_:
+            file_.seek(0, os.SEEK_END)
             while True:
-                curr_position = file_.tell()
-                line = file_.readline()
-                if not line:
-                    file_.seek(curr_position)
-                else:
+                readBuffer.write(file_.read())
+                readBuffer.seek(0)
+                complete = True
+                for line in readBuffer:
+                    if not line.endswith(os.linesep): 
+                        complete = False
+                        break
+
                     self.callback(line)
-                time.sleep(s)
+                    time.sleep(s)
+
+                # Catch the slop if the last line isn't complete
+                readBuffer.truncate(0)
+                if not complete:
+                    if len(line) > self.max_line_length:
+                        raise TailError("Line exceeds maximum allowed line length")
+
+                    readBuffer.write(line)
+                
+                time.sleep(poll_time)
 
     def register_callback(self, func):
         ''' Overrides default callback function to provided function. '''
@@ -71,8 +85,17 @@ def check_file_validity(self, file_):
         if os.path.isdir(file_):
             raise TailError("File '%s' is a directory" % (file_))
 
-class TailError(Exception):
+class TailError(IOError):
     def __init__(self, msg):
         self.message = msg
     def __str__(self):
         return self.message
+
+if __name__ == '__main__':
+    if len(sys.argv) < 2:
+        print "Usage: python tail.py <filename>"
+        sys.exit(1)
+
+    tail = Tail(sys.argv[1])
+    tail.follow(0)
+