Mark5BFileReader

class baseband.mark5b.base.Mark5BFileReader(fh_raw, kday=None, ref_time=None, nchan=None, bps=2)

Bases: baseband.vlbi_base.base.VLBIFileReaderBase

Simple reader for Mark 5B files.

Wraps a binary filehandle, providing methods to help interpret the data, such as read_frame and get_frame_rate.

Parameters

fh_rawfilehandle

Filehandle of the raw binary data file.

kdayint or None

Explicit thousands of MJD of the observation time. Can instead pass an approximate ref_time.

ref_timeTime or None

Reference time within 500 days of the observation time, used to infer the full MJD. Used only if kday is not given.

nchanint, optional

Number of channels. Default: 1.

bpsint, optional

Bits per elementary sample. Default: 2.

Attributes Summary

fh_raw
info()	Standardized information on file readers.

Methods Summary

close(self)
find_header(self, *args, **kwargs)	Find the nearest header from the current position.
get_frame_rate(self)	Determine the number of frames per second.
locate_frames(self[, pattern])	Use a pattern to locate frame starts near the current position.
read_frame(self[, verify])	Read a single frame (header plus payload).
read_header(self)	Read a single header from the file.
temporary_offset(self[, 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
File 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
File 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()

Attributes

formatstr or None

File format, or None if the underlying file cannot be parsed.

number_of_framesint

Number of frames in the file.

frame_rateQuantity

Number of data frames per unit of time.

sample_rateQuantity

Complete samples per unit of time.

samples_per_frameint

Number of complete samples in each frame.

sample_shapetuple

Dimensions of each complete sample (e.g., (nchan,)).

bpsint

Number of bits used to encode each elementary sample.

complex_databool

Whether the data are complex.

start_timeTime

Time of the first complete sample.

readablebool

Whether the first sample could be read and decoded.

missingdict

Entries are keyed by names of arguments that should be passed to the file reader to obtain full information. The associated entries explain why these arguments are needed.

checksdict

Checks that were done to determine whether the file was readable (normally the only entry is ‘decodable’).

errorsdict

Any exceptions raised while trying to determine attributes or doing checks. Keyed by the attributes/checks.

warningsdict

Any warnings about the attributes or about the checks. Keyed by the attributes/checks.

Methods Documentation

close(self)

find_header(self, *args, **kwargs)

Find the nearest header from the current position.

If successful, the file pointer is left at the start of the header.

Parameters are as for locate_frames.

Returns

header

Retrieved header.

Raises

~baseband.vlbi_base.base.HeaderNotFoundError

If no header could be located.

AssertionError

If the header did not pass verification.

get_frame_rate(self)

Determine the number of frames per second.

This method first tries to determine the frame rate by looking for the highest frame number in the first second of data. If that fails, it uses the time difference between two consecutive frames. This can fail if the headers do not store fractional seconds, or if the data rate is above 512 Mbps.

Returns

frame_rateQuantity

Frames per second.

locate_frames(self, pattern=None, **kwargs)

Use a pattern to locate frame starts near the current position.

Note that the current position is always included.

Parameters are as for baseband.vlbi_base.base.VLBIFileReaderBase.locate_frames except that by default the Mark 5B sync pattern is used.

read_frame(self, verify=True)

Read a single frame (header plus payload).

Returns

frameMark5BFrame

With header and data properties that return the Mark5BHeader and data encoded in the frame, respectively.

verifybool, optional

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

read_header(self)

Read a single header from the file.

Returns

headerMark5BHeader

temporary_offset(self, 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().