CkPython Requires Chilkat v11.0.0+

Decompress Large Text File in Blocks

See more Compression Examples

Decompresses a large text file in blocks, and compares the restored (decompressed) file with the original to make sure it's correct. CkPython

import sys
import chilkat

success = False

#  This example requires the Chilkat API to have been previously unlocked.
#  See Global Unlock Sample for sample code.

#  First, let's compress a text file.
#  We'll then decompress in blocks, and compare the decompressed with the original file.

#  Compress a text file:
compress = chilkat.CkCompression()
compress.put_Algorithm("deflate")

success = compress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat")
if (success == False):
    print(compress.lastErrorText())
    sys.exit()

fac = chilkat.CkFileAccess()

#  Examine the uncompressed and compressed sizes:
originalPath = "qa_data/hamlet.xml"
#  Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
#  the size of the file as a string, then convert to an integer value.
print("uncompressed size: " + str(fac.FileSize(originalPath)))
print("compressed size: " + str(fac.FileSize("qa_data/hamlet_compressed.dat")))

#  Decompress in blocks..
facSrc = chilkat.CkFileAccess()
facDest = chilkat.CkFileAccess()

facSrc.OpenForRead("qa_data/hamlet_compressed.dat")

#  If we compress in 32K chunks, find out how many blocks there will be.
blockSize = 32768
numBlocks = facSrc.GetNumBlocks(blockSize)

#  Open an output file for the decompressed data.
restoredPath = "qa_output/hamlet_restored.xml"
success = facDest.OpenForWrite(restoredPath)
if (success == False):
    print(facDest.lastErrorText())
    sys.exit()

compressedBytes = chilkat.CkByteData()

#  Assuming numBlocks > 1
compress.put_FirstChunk(True)
compress.put_LastChunk(False)

i = 0
while i < numBlocks :
    success = facSrc.ReadBlock(i,blockSize,compressedBytes)
    decompressedStr = compress.decompressString(compressedBytes)

    facDest.AppendText(decompressedStr,"utf-8")

    i = i + 1

    compress.put_FirstChunk(False)
    if (i == (numBlocks - 1)):
        compress.put_LastChunk(True)

facSrc.FileClose()
facDest.FileClose()

#  Examine the size of the restored file.
print("restored size: " + str(fac.FileSize(restoredPath)))

#  Compare the contents of the original with the restored.
bEqualContents = fac.FileContentsEqual(restoredPath,originalPath)
print("Contents Equal: " + str(bEqualContents))