TailFollow

TailFollow enables a user to read new data as it is appended to a file in a manner similar to a 'tail -f' command. As a file is moved or rotated (perhaps as part of a log rotation mechanism), TailFollow can continue to read from the file as it moves until a new file is created in the original location.

The simple (non-tracking mode) usage of TailFollow is as follows:

tail = TailFollow("/var/log/syslog")
for line in tail:
    print line,
tail.close()

When tracking changes to a file, usage is as follows:

while 1:
    tail = TailFollow("/var/log/syslog", track=1)
    for line in tail:
        print line,
    time.sleep(1)
tail.close()

It is important to insert a delay to avoid a busy loop in which the TailFollow tries to determine if the file has moved. Failure to do so will result in excessive CPU consumption when the end of file occurs.

class TailFollow(object):

Tail a file and follow as additional data is appended. TailFollow can be used to monitor log files. It can also track when a the file has been moved (perhaps by a log rotation script). In this case, TailFollow will automatically close the old file, and re-open the new file.

__init__(filename, track=1):

Constructor that specifies the file to be tailed. An optional keyword argument specifies whether or not the file should be tracked.

__iter__():

Returns an iterator that can be used to iterate over the lines of the file as they are appended. TailFollow implements the iterator contract, as a result, self is returned to the caller.

next():

Returns the next line from the file being tailed. This method is part of the iterator contract. StopIteration is thrown when there an EOF has been reached.

close():

Closes the current file.