DADAFileReader

class baseband.dada.base.DADAFileReader(fh_raw)

Bases: FileBase

Simple reader for DADA files.

Wraps a binary filehandle, providing methods to help interpret the data, such as read_frame and get_frame_rate. By default, frame payloads are mapped rather than fully read into physical memory.

Parameters:

fh_rawfilehandle

Filehandle of the raw binary data file.

Attributes Summary

fh_raw
info	Standardized information on file readers.

Methods Summary

close()
get_frame_rate()	Determine the number of frames per second.
read_frame([memmap, verify])	Read the frame header and read or map the corresponding payload.
read_header()	Read a single header from the file.
temporary_offset([offset, whence])	Context manager for temporarily seeking to another file position.

Attributes Documentation

fh_raw = None

info

Standardized information on file readers.

The info descriptor has a number of standard attributes, which are determined from arguments passed in opening the file, from the first header (info.header0) and from possibly scanning the file to determine the duration of frames.

Examples

The most common use is simply to print information:

>>> from baseband.data import SAMPLE_MARK5B
>>> from baseband import mark5b
>>> fh = mark5b.open(SAMPLE_MARK5B, 'rb')
>>> fh.info
Mark5BFile information:
format = mark5b
number_of_frames = 4
frame_rate = 6400.0 Hz
bps = 2
complex_data = False
readable = False

missing:  nchan: needed to determine sample shape, frame rate, ...
          kday, ref_time: needed to infer full times.

>>> fh.close()

>>> fh = mark5b.open(SAMPLE_MARK5B, 'rb', kday=56000, nchan=8)
>>> fh.info
Mark5BFile information:
format = mark5b
number_of_frames = 4
frame_rate = 6400.0 Hz
sample_rate = 32.0 MHz
samples_per_frame = 5000
sample_shape = (8,)
bps = 2
complex_data = False
start_time = 2014-06-13T05:30:01.000000000
readable = True

checks:  decodable: True
>>> fh.close()

Methods Documentation

close()

get_frame_rate()

Determine the number of frames per second.

The routine uses the sample rate and number of samples per frame from the first header in the file.

Returns:

frame_rateQuantity

Frames per second.

read_frame(memmap=True, verify=True)

Read the frame header and read or map the corresponding payload.

Parameters:

memmapbool, optional

If True (default), map the payload using memmap, so that parts are only loaded into memory as needed to access data.

verifybool, optional

Whether to do basic checks of frame integrity. Default: True.

Returns:

frameDADAFrame

With .header and .payload properties. The .data property returns all data encoded in the frame. Since this may be too large to fit in memory, it may be better to access the parts of interest by slicing the frame.

read_header()

Read a single header from the file.

Returns:

headerDADAHeader

temporary_offset(offset=None, whence=0)

Context manager for temporarily seeking to another file position.

To be used as part of a with statement:

with fh_raw.temporary_offset() [as fh_raw]:
    with-block

On exiting the with-block, the file pointer is moved back to its original position. As a convenience, one can pass on the offset to seek to when entering the context manager. Parameters are as for io.IOBase.seek().