Created
September 22, 2014 06:41
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def tail( f, lines=20 ): | |
total_lines_wanted = lines | |
BLOCK_SIZE = 1024 | |
f.seek(0, 2) | |
block_end_byte = f.tell() | |
lines_to_go = total_lines_wanted | |
block_number = -1 | |
blocks = [] # blocks of size BLOCK_SIZE, in reverse order starting | |
# from the end of the file | |
while lines_to_go > 0 and block_end_byte > 0: | |
if (block_end_byte - BLOCK_SIZE > 0): | |
# read the last block we haven't yet read | |
f.seek(block_number*BLOCK_SIZE, 2) | |
blocks.append(f.read(BLOCK_SIZE)) | |
else: | |
# file too small, start from begining | |
f.seek(0,0) | |
# only read what was not read | |
blocks.append(f.read(block_end_byte)) | |
lines_found = blocks[-1].count('\n') | |
lines_to_go -= lines_found | |
block_end_byte -= BLOCK_SIZE | |
block_number -= 1 | |
all_read_text = ''.join(reversed(blocks)) | |
return '\n'.join(all_read_text.splitlines()[-total_lines_wanted:]) |
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import os | |
def tail(f, n, offset=0): | |
stdin,stdout = os.popen2("tail -n "+n+offset+" "+f) | |
stdin.close() | |
lines = stdout.readlines(); stdout.close() | |
return lines[:,-offset] |
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