Application programming interface
Exception
- exception PpmdError
This exception is raised when an error occurs.
Simple compression/decompression
This section contains:
function
compress()
function
decompress()
- compress(bytes_or_str: Union[bytes, bytearray, memoryview, str], max_order: int, mem_size: int, variant: str)
Compress bytes_or_str, return the compressed data.
- Parameters
bytes_or_str (bytes-like object or str) – Data to be compressed. When it is type of str, encoded with “UTF-8” encoding before compress.
max_order (int) – maximum order of PPMd algorithm
mem_size (int) – memory size used for building PPMd model
variant (str) – PPMd variant name, only accept “H” or “I”
- Returns
Compressed data
- Return type
bytes
compressed_data = compress(data)
- decompress_str(data: Union[bytes, memoryview], max_order: int, mem_size: int, encoding: str, variant: str)
Decompress data, return the decompressed text.
When encoding specified, return the decoded data as str type by specified encoding. Otherwise it returns data decoding by default “UTF-8”.
- Parameters
data (bytes-like object) – Data to be decompressed.
max_order (int) – maximum order of PPMd algorithm
mem_size (int) – memory size used for building PPMd model
encoding (str) – Encoding name to use when decoding raw decompressed data
variant (str) – PPMd variant name, only accept “H” or “I”
- Returns
Decompressed text
- Return type
str
- Raises
PpmdError – If decompression fails.
decompressed_text = decompress_str(data)
- decompress(data: Union[bytes, memoryview], max_order: int, mem_size: int, variant: str)
Decompress data, return the decompressed data.
- Parameters
data (bytes-like object) – Data to be decompressed
max_order (int) – maximum order of PPMd algorithm
mem_size (int) – memory size used for building PPMd model
variant (str) – PPMd variant name, only accept “H” or “I”
- Returns
Decompressed data
- Return type
bytes
- Raises
PpmdError – If decompression fails.
decompressed_data = decompress(data)
Streaming compression
- class PpmdCompressor
A streaming compressor. It’s thread-safe at method level.
- __init__(self, max_order: int, mem_size: int, variant: str, restore_method: int)
Initialize a PpmdCompressor object. restore_method param is affected only when variant is “I”.
- Parameters
max_order (int) – maximum order of PPMd algorithm
mem_size (int) – memory size used for building PPMd model
variant (str) – PPMd variant name, only accept “H” or “I”
restore_method (int) – PPMD8_RESTORE_METHOD_RESTART(0) or PPMD8_RESTORE_METHOD_CUTOFF(1)
- compress(self, data)
Provide data to the compressor object.
- Parameters
data (bytes-like object) – Data to be compressed.
- Returns
A chunk of compressed data if possible, or
b''
otherwise.- Return type
bytes
- flush(self)
Flush any remaining data in internal buffer.
The compressor object can not be used after this method is called.
- Returns
Flushed data.
- Return type
bytes
c = PpmdCompressor() dat1 = c.compress(b'123456') dat2 = c.compress(b'abcdef') dat3 = c.flush()
Streaming decompression
- class PpmdDecompressor
A streaming decompressor. Thread-safe at method level. A restore_method param is affected only when variant is “I”.
- __init__(self, max_order: int, mem_size: int, variant: str, restore_method: int)
Initialize a PpmdDecompressor object.
- Parameters
max_order (int) – maximum order of PPMd algorithm
mem_size (int) – memory size used for building PPMd model
variant (str) – PPMd variant name, only accept “H” or “I”
restore_method (int) – PPMD8_RESTORE_METHOD_RESTART(0) or PPMD8_RESTORE_METHOD_CUTOFF(1)
- decompress(self, data, max_length=-1)
Decompress data, returning decompressed data as a
bytes
object.- Parameters
data (bytes-like object) – Data to be decompressed.
max_length (int) – Maximum size of returned data. When it’s negative, the output size is unlimited. When it’s non-negative, returns at most max_length bytes of decompressed data. If this limit is reached and further output can (or may) be produced, the
needs_input
attribute will be set toFalse
. In this case, the next call to this method may provide data asb''
to obtain more of the output.
- needs_input
If the max_length output limit in
decompress()
method has been reached, and the decompressor has (or may has) unconsumed input data, it will be set toFalse
. In this case, passb''
todecompress()
method may output further data.If ignore this attribute when there is unconsumed input data, there will be a little performance loss because of extra memory copy. This flag can be True even all input data are consumed, when decompressor can be able to accept more data in some case.
- eof
True
means the end of the first frame has been reached. If decompress data after that, anEOFError
exception will be raised. This flag can be False even all input data are consumed, when decompressor can be able to accept more data in some case.
- unused_data
A bytes object. When PpmdDecompressor object stops after end mark, unused input data after the end mark. Otherwise this will be
b''
.
d1 = PpmdDecompressor() decompressed_dat = d1.decompress(dat1) decompressed_dat += d1.decompress(dat2) decompressed_dat += d1.decompress(dat3)