DADAFileReader¶
-
class
baseband.dada.base.
DADAFileReader
(fh_raw)[source] [edit on github]¶ Bases:
baseband.vlbi_base.base.VLBIFileReaderBase
Simple reader for DADA files.
Wraps a binary filehandle, providing methods to help interpret the data, such as
read_frame
andget_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
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, \*[, mask, …])Use a pattern to locate frame starts near the current position.
read_frame
(self[, memmap, verify])Read the frame header and read or map the corresponding payload.
read_header
(self)Read a single header from the file.
temporary_offset
(self)Context manager for temporarily seeking to another file position.
Attributes Documentation
-
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_rate
Quantity
Number of data frames per unit of time.
- sample_rate
Quantity
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_time
Time
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.
- formatstr or
Methods Documentation
-
close
(self) [edit on github]¶
-
find_header
(self, *args, **kwargs) [edit on github]¶ 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)[source] [edit on github]¶ 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_rate
Quantity
Frames per second.
- frame_rate
-
locate_frames
(self, pattern, *, mask=None, frame_nbytes=None, offset=0, forward=True, maximum=None, check=1) [edit on github]¶ Use a pattern to locate frame starts near the current position.
Note that the current position is always included.
- Parameters
- patternheader, ~numpy.ndaray, bytes, int, or iterable of int
Synchronization pattern to look for. If a header or header class,
invariant_pattern()
is used to create a masked pattern, using invariant keys frominvariants()
. If anndarray
orbytes
instance, a byte array view is taken. If an (iterable of) int, the integers need to be unsigned 32 bit and will be interpreted as little-endian.- mask~numpy.ndarray, bytes, int, or iterable of int.
Bit mask for the pattern, with 1 indicating a given bit will be used the comparison.
- frame_nbytesint, optional
Frame size in bytes. Defaults to the frame size in any header passed in.
- offsetint, optional
Offset from the frame start that the pattern occurs. Any offsets inferred from masked entries are added to this (hence, no offset needed when a header is passed in as
pattern
).- forwardbool, optional
- maximumint, optional
Maximum number of bytes to search away from the present location. Default: search twice the frame size if given, otherwise 1 million (extra bytes to avoid partial patterns will be added). Use 0 to check only at the current position.
- checkint or tuple of int, optional
Frame offsets where another sync pattern should be present (if inside the file). Ignored if
frame_nbytes
is not given. Default: 1, i.e., a sync pattern should be present one frame after the one found (independent offorward
), thus helping to guarantee the frame is not corrupted.
- Returns
- locationslist of int
Locations of sync patterns within the range scanned, in order of proximity to the starting position.
-
read_frame
(self, memmap=True, verify=True)[source] [edit on github]¶ Read the frame header and read or map the corresponding payload.
- Parameters
- Returns
- frame
DADAFrame
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.
- frame
-
read_header
(self)[source] [edit on github]¶ Read a single header from the file.
- Returns
- header
DADAHeader
- header
-
temporary_offset
(self) [edit on github]¶ 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.