StreamWriterBase

class baseband.base.base.StreamWriterBase(fh_raw, header0, *, squeeze=True, **kwargs)

Bases: StreamBase

Base for all stream writers, providing a standard write method.

Parameters:

fh_rawfilehandle

Should be opened in binary mode for writer, and usually wrapped in a given format’s FileWriter.

header0header instance

Header for the first frame, holding time information, etc. Can instead give keyword arguments to construct a header (see **kwargs).

squeezebool, optional

If True (default), writer accepts squeezed arrays as input, and adds any dimensions of length unity.

**kwargs

Information that supplements that of the header. In particular, any format should define bps, complex_data, samples_per_frame, sample_shape (on file), and sample_rate.

Notes

Accessing frames happens via a number of private methods, which can be overridden by subclasses to deal with their peculiarities.

The process starts in write with _get_frame(offset), which determines the index of the frame a given offset falls in, and then either uses _make_frame(index) to create it, or returns a possibly cached frame, together with the sample_offset at which offset falls within the frame. Then, data is inserted as needed until the frame is exhausted, at which point the frame is written to disk using _fh_raw_write_frame and the process repeats.

Various formats override various steps. For instance, for DADA and GUPPI, _make_frame() and _fh_raw_write_frame() are overridden to work with memory mapped files. For GSB, _fh_raw_write_frame() is overridden to take into account that header and data are read from different files.

Attributes Summary

bps	Bits per elementary sample.
complex_data	Whether the data are complex.
header0	First header of the file.
sample_rate	Number of complete samples per second.
sample_shape	Shape of a complete sample (possibly subset or squeezed).
samples_per_frame	Number of complete samples per frame.
squeeze	Whether data arrays have dimensions with length unity removed.
start_time	Start time of the file.
time	Time of the sample pointer's current offset in file.

Methods Summary

close()
tell([unit])	Current offset in the file.
write(data[, valid])	Write data, buffering by frames as needed.

Attributes Documentation

bps

Bits per elementary sample.

complex_data

Whether the data are complex.

header0

First header of the file.

sample_rate

Number of complete samples per second.

sample_shape

Shape of a complete sample (possibly subset or squeezed).

samples_per_frame

Number of complete samples per frame.

squeeze

Whether data arrays have dimensions with length unity removed.

If True, data read out has such dimensions removed, and data passed in for writing has them inserted.

start_time

Start time of the file.

See also time for the time of the sample pointer’s current offset.

time

Time of the sample pointer’s current offset in file.

See also start_time for the start time of the file.

Methods Documentation

close()

tell(unit=None)

Current offset in the file.

Parameters:

unitUnit or str, optional

Time unit the offset should be returned in. By default, no unit is used, i.e., an integer enumerating samples is returned. For the special string ‘time’, the absolute time is calculated.

Returns:

offsetint, Quantity, or Time

Offset in current file (or time at current position).

write(data, valid=True)

Write data, buffering by frames as needed.

Parameters:

datandarray

Piece of data to be written, with sample dimensions as given by sample_shape. This should be properly scaled to make best use of the dynamic range delivered by the encoding.

validbool, optional

Whether the current data are valid. Default: True.