## 12.3.1 (De)compression of files

Handling of compressed files is offered by the `BZ2File` class.

class `BZ2File`( | filename[, mode[, buffering[, compresslevel]]])

  Open a bz2 file. Mode can be either `'r'` or `'w'`, for reading (default) or writing. When opened for writing, the file will be created if it doesn't exist, and truncated otherwise. If buffering is given, `0` means unbuffered, and larger numbers specify the buffer size; the default is `0`. If compresslevel is given, it must be a number between `1` and `9`; the default is `9`. Add a "`U`" to mode to open the file for input with universal newline support. Any line ending in the input file will be seen as a "`\n`" in Python. Also, a file so opened gains the attribute `newlines`; the value for this attribute is one of `None` (no newline read yet), `'\r'`, `'\n'`, `'\r\n'` or a tuple containing all the newline types seen. Universal newlines are available only when reading. Instances support iteration in the same way as normal `file` instances.

`close`( | )

  Close the file. Sets data attribute `closed` to true. A closed file cannot be used for further I/O operations. `close()` may be called more than once without error.

`read`( | [size])

  Read at most size uncompressed bytes, returned as a string. If the size argument is negative or omitted, read until EOF is reached.

`readline`( | [size])

  Return the next line from the file, as a string, retaining newline. A non-negative size argument limits the maximum number of bytes to return (an incomplete line may be returned then). Return an empty string at EOF.

`readlines`( | [size])

  Return a list of lines read. The optional size argument, if given, is an approximate bound on the total number of bytes in the lines returned.

`xreadlines`( | )

  For backward compatibility. `BZ2File` objects now include the performance optimizations previously implemented in the `xreadlines` module.
  Deprecated since release 2.3. This exists only for compatibility with the method by this name on `file` objects, which is deprecated. Use `for line in file` instead.

`seek`( | offset[, whence])

  Move to new file position. Argument offset is a byte count. Optional argument whence defaults to `os.SEEK_SET` or `0` (offset from start of file; offset should be `>= 0`); other values are `os.SEEK_CUR` or `1` (move relative to current position; offset can be positive or negative), and `os.SEEK_END` or `2` (move relative to end of file; offset is usually negative, although many platforms allow seeking beyond the end of a file).

  Note that seeking of bz2 files is emulated, and depending on the parameters the operation may be extremely slow.

`tell`( | )

  Return the current file position, an integer (may be a long integer).

`write`( | data)

  Write string data to file. Note that due to buffering, `close()` may be needed before the file on disk reflects the data written.

`writelines`( | sequence_of_strings)

  Write the sequence of strings to the file. Note that newlines are not added. The sequence can be any iterable object producing strings. This is equivalent to calling write() for each string.