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#!/usr/bin/python2
 
 
"""Tests different versions to implement tail (except seek or mmap)
 
Results for python-2.7, linux x86_64:
 
20940 lines, average line length 163:
dequetail       3.69968
listtail        5.02768
 
Performance seems largely independent of requested number of lines
"""
 
import collections
import sys
import timeit
 
 
def tail(filename, count, method):
    with open(filename, 'r') as filein:
        return method(filein, count)
 
 
def dequetail(filein, count):
    return collections.deque(filein, count)
 
 
def listtail(filein, count):
    lines = list()
    readlines = filein.readlines
    while True:
        block = readlines(8196)
        if block:
            replaced = max(0, len(block) + len(lines) - count)
            del lines[:replaced]
            lines += block
        else:
            break
    del lines[:-count]
    return lines
 
 
def test(methods, filename, count):
    results = ((method, list(tail(filename, count, method))) for method
               in methods)
    _, trusted = next(results)
    wrongs = (method.__name__ for method, result in results
              if result != trusted)
    messages = ("%s failed\n" % method for method in wrongs)
    sys.stderr.writelines(messages)
 
 
filename = None
 
def main():
    global filename
    filename = sys.argv[1]
    count = 100
    methods = (dequetail, listtail)
    test(methods, filename, count)
    methodnames = [method.__name__ for method in methods]
    setups = ('from __main__ import %s, tail, filename' % method for method
              in methodnames)
    stmts = ("tail(filename, %d, %s)" % (count, method) for method
             in methodnames)
    times = (timeit.timeit(setup=setup, stmt=stmt, number=1000)
             for setup, stmt in zip(setups, stmts))
    output = ("%s\t%g\n" % (method, time) for method, time
              in zip(methodnames, times))
    sys.stderr.writelines(output)
 
 
if __name__ == '__main__':
    main()