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#!/usr/bin/env python
#
# Sort large text files in a minimum amount of memory
#
importargparse
importos
classFileSplitter:
BLOCK_FILENAME_FORMAT="block_{0}.dat"
def__init__(self, filename):
self.filename=filename
self.block_filenames= []
defwrite_block(self, data, block_number):
filename=self.BLOCK_FILENAME_FORMAT.format(block_number)
withopen(filename, "w") asfile:
file.write(data)
self.block_filenames.append(filename)
defget_block_filenames(self):
returnself.block_filenames
defsplit(self, block_size, sort_key=None):
i=0
withopen(self.filename) asfile:
whileTrue:
lines=file.readlines(block_size)
iflines== []:
break
ifsort_keyisNone:
lines.sort()
else:
lines.sort(key=sort_key)
self.write_block("".join(lines), i)
i+=1
defcleanup(self):
map(os.remove, self.block_filenames)
classNWayMerge:
defselect(self, choices):
min_index=-1
min_str=None
foriinrange(len(choices)):
ifmin_strisNoneorchoices[i] <min_str:
min_index=i
returnmin_index
classFilesArray:
def__init__(self, files):
self.files=files
self.empty=set()
self.num_buffers=len(files)
self.buffers= {i: Noneforiinrange(self.num_buffers)}
defget_dict(self):
return {
i: self.buffers[i] foriinrange(self.num_buffers) ifinotinself.empty
}
defrefresh(self):
foriinrange(self.num_buffers):
ifself.buffers[i] isNoneandinotinself.empty:
self.buffers[i] =self.files[i].readline()
ifself.buffers[i] =="":
self.empty.add(i)
self.files[i].close()
iflen(self.empty) ==self.num_buffers:
returnFalse
returnTrue
defunshift(self, index):
value=self.buffers[index]
self.buffers[index] =None
returnvalue
classFileMerger:
def__init__(self, merge_strategy):
self.merge_strategy=merge_strategy
defmerge(self, filenames, outfilename, buffer_size):
buffers=FilesArray(self.get_file_handles(filenames, buffer_size))
withopen(outfilename, "w", buffer_size) asoutfile:
whilebuffers.refresh():
min_index=self.merge_strategy.select(buffers.get_dict())
outfile.write(buffers.unshift(min_index))
defget_file_handles(self, filenames, buffer_size):
files= {}
foriinrange(len(filenames)):
files[i] =open(filenames[i], "r", buffer_size) # noqa: UP015
returnfiles
classExternalSort:
def__init__(self, block_size):
self.block_size=block_size
defsort(self, filename, sort_key=None):
num_blocks=self.get_number_blocks(filename, self.block_size)
splitter=FileSplitter(filename)
splitter.split(self.block_size, sort_key)
merger=FileMerger(NWayMerge())
buffer_size=self.block_size/ (num_blocks+1)
merger.merge(splitter.get_block_filenames(), filename+".out", buffer_size)
splitter.cleanup()
defget_number_blocks(self, filename, block_size):
return (os.stat(filename).st_size/block_size) +1
defparse_memory(string):
ifstring[-1].lower() =="k":
returnint(string[:-1]) *1024
elifstring[-1].lower() =="m":
returnint(string[:-1]) *1024*1024
elifstring[-1].lower() =="g":
returnint(string[:-1]) *1024*1024*1024
else:
returnint(string)
defmain():
parser=argparse.ArgumentParser()
parser.add_argument(
"-m", "--mem", help="amount of memory to use for sorting", default="100M"
)
parser.add_argument(
"filename", metavar="<filename>", nargs=1, help="name of file to sort"
)
args=parser.parse_args()
sorter=ExternalSort(parse_memory(args.mem))
sorter.sort(args.filename[0])
if__name__=="__main__":
main()