VLBIStreamReaderBase

class baseband.base.base.VLBIStreamReaderBase(fh_raw, header0, **kwargs)

Bases: StreamReaderBase

Base for VLBI stream readers.

This extends the base class specifically for the case that the underlying file has small subsequent frames, which may have gaps, and adds methods that allow fixing these.

Arguments are as for StreamReaderBase.

Notes

The code assumes that the raw file reader has a find_header method, which can be used to find next or previous frames from any position, and thus help identify and skip bad frames. It is used in _last_header to be sure to find a full last frame.

The class also overrides the _read_frame method which one that checks that the frame after the one requested is the right one, and attemps recovery if anything fails, using _bad_frame(index, frame, exc).

Subclasses can overrides parts of the class. For instance, VDIF overrides _fh_raw_read_frame and _bad_frame to take care of the fact that data comes in sets of frames from multiple threads, not individual ones.

Attributes Summary

bps	Bits per elementary sample.
complex_data	Whether the data are complex.
dtype
fill_value	Value to use for invalid or missing data.
header0	First header of the file.
info	Standardized information on stream readers.
ndim	Number of dimensions of the (squeezed/subset) stream data.
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.
shape	Shape of the (squeezed/subset) stream data.
size	Total number of component samples in the (squeezed/subset) stream data.
squeeze	Whether data arrays have dimensions with length unity removed.
start_time	Start time of the file.
stop_time	Time at the end of the file, just after the last sample.
subset	Specific components of the complete sample to decode.
time	Time of the sample pointer's current offset in file.
verify	Whether to do consistency checks on frames being read.

Methods Summary

close()
read([count, out])	Read a number of complete samples.
readable()	Whether the file can be read and decoded.
seek(offset[, whence])	Change the sample pointer position.
tell([unit])	Current offset in the file.

Attributes Documentation

bps

Bits per elementary sample.

complex_data

Whether the data are complex.

dtype

fill_value

Value to use for invalid or missing data. Default: 0.

header0

First header of the file.

info

Standardized information on stream readers.

The info descriptor provides a few standard attributes, most of which can also be accessed directly on the stream filehandle, and tests basic readability of the stream. More detailed information on the underlying file is stored in its info, accessible via info.file_info (and shown by __repr__).

ndim

Number of dimensions of the (squeezed/subset) stream data.

sample_rate

sample_shape

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

samples_per_frame

Number of complete samples per frame.

shape

Shape of the (squeezed/subset) stream data.

size

Total number of component samples in the (squeezed/subset) stream data.

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, and (if available) stop_time for the time at the end of the file.

stop_time

Time at the end of the file, just after the last sample.

See also start_time for the start time of the file, and time for the time of the sample pointer’s current offset.

subset

Specific components of the complete sample to decode.

The order of dimensions is the same as for sample_shape. Set by the class initializer.

time

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

See also start_time for the start time, and (if available) stop_time for the end time, of the file.

verify

Whether to do consistency checks on frames being read.

Methods Documentation

close()

read(count=None, out=None)

Read a number of complete samples.

Parameters:

countint or None, optional

Number of complete samples to read. If None (default) or negative, the number of samples left. Ignored if out is given.

outNone or array, optional

Array to store the samples in. If given, count will be inferred from the first dimension; the remaining dimensions should equal sample_shape.

Returns:

outndarray of float or complex

The first dimension is sample-time, and the remaining ones are as given by sample_shape.

readable()

Whether the file can be read and decoded.

seek(offset, whence=0)

Change the sample pointer position.

This works like a normal filehandle seek, but the offset is in samples (or a relative or absolute time).

Parameters:

offsetint, Quantity, or Time

Offset to move to. Can be an (integer) number of samples, an offset in time units, or an absolute time. For the latter two, the pointer will be moved to the nearest integer sample.

whence{0, 1, 2, ‘start’, ‘current’, or ‘end’}, optional

Like regular seek, the offset is taken to be from the start if whence=0 (default), from the current position if 1, and from the end if 2. One can alternativey use ‘start’, ‘current’, or ‘end’ for 0, 1, or 2, respectively. Ignored if offset is a time.

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).