compressor package

Submodules

Module contents

compressor entry point

lib module

compressor.lib

High-level functions exposed as a library, that can be imported.

compressor.lib.compress_file(filename: str, dest_file: str = '') → None

Open the <filename> and compress its contents on a new one.

Parameters:

• filename (str) – The path to the source file to compress.
• dest_file (str) – The name of the target file. If not provided (None), a default will be used with <filename>.comp

compressor.lib.open_text_file()

Open file and return a stream. Raise OSError upon failure.

file is either a text or byte string giving the name (and the path if the file isn’t in the current working directory) of the file to be opened or an integer file descriptor of the file to be wrapped. (If a file descriptor is given, it is closed when the returned I/O object is closed, unless closefd is set to False.)

mode is an optional string that specifies the mode in which the file is opened. It defaults to ‘r’ which means open for reading in text mode. Other common values are ‘w’ for writing (truncating the file if it already exists), ‘x’ for creating and writing to a new file, and ‘a’ for appending (which on some Unix systems, means that all writes append to the end of the file regardless of the current seek position). In text mode, if encoding is not specified the encoding used is platform dependent: locale.getpreferredencoding(False) is called to get the current locale encoding. (For reading and writing raw bytes use binary mode and leave encoding unspecified.) The available modes are:

Character	Meaning
‘r’	open for reading (default)
‘w’	open for writing, truncating the file first
‘x’	create a new file and open it for writing
‘a’	open for writing, appending to the end of the file if it exists
‘b’	binary mode
‘t’	text mode (default)
‘+’	open a disk file for updating (reading and writing)
‘U’	universal newline mode (deprecated)

The default mode is ‘rt’ (open for reading text). For binary random access, the mode ‘w+b’ opens and truncates the file to 0 bytes, while ‘r+b’ opens the file without truncation. The ‘x’ mode implies ‘w’ and raises an FileExistsError if the file already exists.

Python distinguishes between files opened in binary and text modes, even when the underlying operating system doesn’t. Files opened in binary mode (appending ‘b’ to the mode argument) return contents as bytes objects without any decoding. In text mode (the default, or when ‘t’ is appended to the mode argument), the contents of the file are returned as strings, the bytes having been first decoded using a platform-dependent encoding or using the specified encoding if given.

‘U’ mode is deprecated and will raise an exception in future versions of Python. It has no effect in Python 3. Use newline to control universal newlines mode.

buffering is an optional integer used to set the buffering policy. Pass 0 to switch buffering off (only allowed in binary mode), 1 to select line buffering (only usable in text mode), and an integer > 1 to indicate the size of a fixed-size chunk buffer. When no buffering argument is given, the default buffering policy works as follows:

• Binary files are buffered in fixed-size chunks; the size of the buffer is chosen using a heuristic trying to determine the underlying device’s “block size” and falling back on io.DEFAULT_BUFFER_SIZE. On many systems, the buffer will typically be 4096 or 8192 bytes long.
• “Interactive” text files (files for which isatty() returns True) use line buffering. Other text files use the policy described above for binary files.

encoding is the name of the encoding used to decode or encode the file. This should only be used in text mode. The default encoding is platform dependent, but any encoding supported by Python can be passed. See the codecs module for the list of supported encodings.

errors is an optional string that specifies how encoding errors are to be handled—this argument should not be used in binary mode. Pass ‘strict’ to raise a ValueError exception if there is an encoding error (the default of None has the same effect), or pass ‘ignore’ to ignore errors. (Note that ignoring encoding errors can lead to data loss.) See the documentation for codecs.register or run ‘help(codecs.Codec)’ for a list of the permitted encoding error strings.

newline controls how universal newlines works (it only applies to text mode). It can be None, ‘’, ‘n’, ‘r’, and ‘rn’. It works as follows:

• On input, if newline is None, universal newlines mode is enabled. Lines in the input can end in ‘n’, ‘r’, or ‘rn’, and these are translated into ‘n’ before being returned to the caller. If it is ‘’, universal newline mode is enabled, but line endings are returned to the caller untranslated. If it has any of the other legal values, input lines are only terminated by the given string, and the line ending is returned to the caller untranslated.
• On output, if newline is None, any ‘n’ characters written are translated to the system default line separator, os.linesep. If newline is ‘’ or ‘n’, no translation takes place. If newline is any of the other legal values, any ‘n’ characters written are translated to the given string.

If closefd is False, the underlying file descriptor will be kept open when the file is closed. This does not work when a file name is given and must be True in that case.

A custom opener can be used by passing a callable as opener. The underlying file descriptor for the file object is then obtained by calling opener with (file, flags). opener must return an open file descriptor (passing os.open as opener results in functionality similar to passing None).

open() returns a file object whose type depends on the mode, and through which the standard file operations such as reading and writing are performed. When open() is used to open a file in a text mode (‘w’, ‘r’, ‘wt’, ‘rt’, etc.), it returns a TextIOWrapper. When used to open a file in a binary mode, the returned class varies: in read binary mode, it returns a BufferedReader; in write binary and append binary modes, it returns a BufferedWriter, and in read/write mode, it returns a BufferedRandom.

It is also possible to use a string or bytearray as a file for both reading and writing. For strings StringIO can be used like a file opened in a text mode, and for bytes a BytesIO can be used like a file opened in a binary mode.

cli module

Compressor CLI (command-line interface) module. Exposes the entry point to the program for executing as command line.

compressor.cli.argument_parser() → argparse.ArgumentParser

Create the argument parser object to be used for parsing the arguments from sys.argv

compressor.cli.main() → int

Program cli

Returns:Status code of the program. Return type:int

compressor.cli.main_engine(filename: str, extract: bool = False, compress: bool = True, dest_file=None) → int

Main functionality for the program cli or call as library. extract & compress must have opposite values.

Return type:

int

Parameters:

• filename (str) – Path to the source file to process.
• extract (bool) – If True, sets the program for a extraction.
• compress (bool) – If True, the program should compress a file.
• dest_file – Optional name of the target file.

Returns:

0 if executed without problems.

compressor.cli.parse_arguments(args=None) → dict

Parse the command-line (cli) provided arguments, and return a mapping of the options selected by the user with their values.

Returns:dict with the kwargs provided in cli

compressor.core module

compressor.core

Low-level functionality with the core of the process that the main program makes use of.

It contains auxiliary functions.

compressor.core.compress_and_save_content(input_filename: str, output_file: io, table: dict) → None

Opens and processes <input_filename>. Iterates over the file and writes the contents on output_file.

Parameters:

• input_filename (str) – the source to be compressed
• output_file (io) – opened file where to write the outcome
• table (dict) – mapping table for the char encoding

compressor.core.create_tree_code(charset: List[compressor.char_node.CharNode]) → compressor.char_node.CharNode

Receives a :list: of :CharNode: (characters) charset, namely leaves in the tree, and returns a tree with the corresponding prefix-free code.

Return type:CharNode Parameters:charset – iterable with all the characters to process. Returns:iterable with a tree of the prefix-free code for the charset.

compressor.core.decode_file_content(compfile: io, table: dict, checksum: int) → str

Reconstruct the remaining part of the <compfile>, starting right after the metadata, decoding each bit according to the <table>.

compressor.core.open_text_file()

Open file and return a stream. Raise OSError upon failure.

file is either a text or byte string giving the name (and the path if the file isn’t in the current working directory) of the file to be opened or an integer file descriptor of the file to be wrapped. (If a file descriptor is given, it is closed when the returned I/O object is closed, unless closefd is set to False.)

mode is an optional string that specifies the mode in which the file is opened. It defaults to ‘r’ which means open for reading in text mode. Other common values are ‘w’ for writing (truncating the file if it already exists), ‘x’ for creating and writing to a new file, and ‘a’ for appending (which on some Unix systems, means that all writes append to the end of the file regardless of the current seek position). In text mode, if encoding is not specified the encoding used is platform dependent: locale.getpreferredencoding(False) is called to get the current locale encoding. (For reading and writing raw bytes use binary mode and leave encoding unspecified.) The available modes are:

Character	Meaning
‘r’	open for reading (default)
‘w’	open for writing, truncating the file first
‘x’	create a new file and open it for writing
‘a’	open for writing, appending to the end of the file if it exists
‘b’	binary mode
‘t’	text mode (default)
‘+’	open a disk file for updating (reading and writing)
‘U’	universal newline mode (deprecated)

The default mode is ‘rt’ (open for reading text). For binary random access, the mode ‘w+b’ opens and truncates the file to 0 bytes, while ‘r+b’ opens the file without truncation. The ‘x’ mode implies ‘w’ and raises an FileExistsError if the file already exists.

Python distinguishes between files opened in binary and text modes, even when the underlying operating system doesn’t. Files opened in binary mode (appending ‘b’ to the mode argument) return contents as bytes objects without any decoding. In text mode (the default, or when ‘t’ is appended to the mode argument), the contents of the file are returned as strings, the bytes having been first decoded using a platform-dependent encoding or using the specified encoding if given.

‘U’ mode is deprecated and will raise an exception in future versions of Python. It has no effect in Python 3. Use newline to control universal newlines mode.

buffering is an optional integer used to set the buffering policy. Pass 0 to switch buffering off (only allowed in binary mode), 1 to select line buffering (only usable in text mode), and an integer > 1 to indicate the size of a fixed-size chunk buffer. When no buffering argument is given, the default buffering policy works as follows:

• Binary files are buffered in fixed-size chunks; the size of the buffer is chosen using a heuristic trying to determine the underlying device’s “block size” and falling back on io.DEFAULT_BUFFER_SIZE. On many systems, the buffer will typically be 4096 or 8192 bytes long.
• “Interactive” text files (files for which isatty() returns True) use line buffering. Other text files use the policy described above for binary files.

encoding is the name of the encoding used to decode or encode the file. This should only be used in text mode. The default encoding is platform dependent, but any encoding supported by Python can be passed. See the codecs module for the list of supported encodings.

errors is an optional string that specifies how encoding errors are to be handled—this argument should not be used in binary mode. Pass ‘strict’ to raise a ValueError exception if there is an encoding error (the default of None has the same effect), or pass ‘ignore’ to ignore errors. (Note that ignoring encoding errors can lead to data loss.) See the documentation for codecs.register or run ‘help(codecs.Codec)’ for a list of the permitted encoding error strings.

newline controls how universal newlines works (it only applies to text mode). It can be None, ‘’, ‘n’, ‘r’, and ‘rn’. It works as follows:

• On input, if newline is None, universal newlines mode is enabled. Lines in the input can end in ‘n’, ‘r’, or ‘rn’, and these are translated into ‘n’ before being returned to the caller. If it is ‘’, universal newline mode is enabled, but line endings are returned to the caller untranslated. If it has any of the other legal values, input lines are only terminated by the given string, and the line ending is returned to the caller untranslated.
• On output, if newline is None, any ‘n’ characters written are translated to the system default line separator, os.linesep. If newline is ‘’ or ‘n’, no translation takes place. If newline is any of the other legal values, any ‘n’ characters written are translated to the given string.

If closefd is False, the underlying file descriptor will be kept open when the file is closed. This does not work when a file name is given and must be True in that case.

A custom opener can be used by passing a callable as opener. The underlying file descriptor for the file object is then obtained by calling opener with (file, flags). opener must return an open file descriptor (passing os.open as opener results in functionality similar to passing None).

open() returns a file object whose type depends on the mode, and through which the standard file operations such as reading and writing are performed. When open() is used to open a file in a text mode (‘w’, ‘r’, ‘wt’, ‘rt’, etc.), it returns a TextIOWrapper. When used to open a file in a binary mode, the returned class varies: in read binary mode, it returns a BufferedReader; in write binary and append binary modes, it returns a BufferedWriter, and in read/write mode, it returns a BufferedRandom.

It is also possible to use a string or bytearray as a file for both reading and writing. For strings StringIO can be used like a file opened in a text mode, and for bytes a BytesIO can be used like a file opened in a binary mode.

compressor.core.parse_tree_code(tree: compressor.char_node.CharNode, table: dict = None, code: bytes = b'') → dict

Given the tree with the chars-frequency processed, return a table that maps each character with its binary representation on the new code:

left –> 0

right –> 1

Return type:

dict

Parameters:

• tree (CharNode) – iterable with the tree as returned by create_tree_code
• table (dict) – Map with the translation for the characters to its code in the new system (prefix-free).
• code (bytes) – The code prefix so far.

Returns:

Mapping with with the original char to its new code.

compressor.core.process_frequencies(stream: Sequence[str]) → List[compressor.char_node.CharNode]

Given a stream of text, return a list of CharNode with the frequencies for each character.

Parameters:stream – sequence with all the characters.

compressor.core.process_line_compression(buffer_line: str, output_file: io, table: dict) → None

Transform buffer_line into the new code, per-byte, based on table and save the new byte-stream into output_file.

Parameters:

• buffer_line (str) – a chunk of the text to process.
• output_file (io) – The opened file where to write the result.
• table (dict) – Translation table for the characters in buffer_line.

compressor.core.retrieve_compressed_file(filename: str, dest_file: str = '') → None

EXTRACT - Reconstruct the original file from the compressed copy. Reads a binary file. Writes into a text file. Write the output in the indicated dest_file.

compressor.core.retrieve_table(dest_file: io) → dict

Read the binary file, and return the translation table as a reversed dictionary.

compressor.core.save_compressed_file(filename: str, table: dict, checksum: int, dest_file: str = '') → None

Given the original file by its filename, save a new one. table contains the new codes for each character on filename.

compressor.core.save_table(dest_file: io, table: dict) → None

Store the table in the destination file.

c: char L: code of c (unsigned Long)

Parameters:

• dest_file (io) – opened file where to write the table.
• table (dict) – Mapping table with the chars and their codes.

functions module