VDIFFileReader¶
- class baseband.vdif.base.VDIFFileReader(fh_raw)[source] [edit on github]¶
Bases:
VLBIFileReaderBase
Simple reader for VDIF files.
Wraps a binary filehandle, providing methods to help interpret the data, such as
read_frame
,read_frameset
andget_frame_rate
.- Parameters:
- fh_rawfilehandle
Filehandle of the raw binary data file.
Attributes Summary
Methods Summary
close
()find_header
([pattern, edv, mask, ...])Find the nearest header from the current position.
Determine the number of frames per second.
get_thread_ids
([check])Determine the number of threads in the VDIF file.
locate_frames
(pattern, *[, mask, ...])Use a pattern to locate frame starts near the current position.
read_frame
([edv, verify])Read a single frame (header plus payload).
read_frameset
([thread_ids, edv, verify])Read a single frame (header plus payload).
read_header
([edv, verify])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¶
Methods Documentation
- close() [edit on github]¶
- find_header(pattern=None, *, edv=None, mask=None, frame_nbytes=None, offset=0, forward=True, maximum=None, check=1)[source] [edit on github]¶
Find the nearest header from the current position.
Search for a valid header at a given position which is consistent with
pattern
and/or with a header a frame size ahead. Note that the search is much slower if no pattern is given, as at every position it is tried to read a header, and then check for another one one frame ahead. It helps to pass inedv
andframe_nbytes
(if known).If successful, the file pointer is left at the start of the header.
- Parameters:
- pattern
VDIFHeader
, array of byte, or compatible If given, used for a direct search.
- edvint
EDV of the header, used if
pattern
is not given.- maskarray of byte, bytes, iterable of int, string or int
Bit mask for the pattern, with 1 indicating a given bit will be used the comparison. Only used with
pattern
and not needed ifpattern
is a header.- 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
, nor is an offset needed for a full search).- forwardbool, optional
- maximumint, optional
Maximum number of bytes to search away from the present location. Default: search twice the frame size if given, otherwise 10000 (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 header should be present. Default: 1, i.e., a sync pattern should be present one frame after the one found (independent of
forward
), thus helping to guarantee the frame is not corrupted.
- pattern
- Returns:
- header
VDIFHeader
Retrieved VDIF header.
- header
- Raises:
- ~baseband.base.base.HeaderNotFoundError
If no header could be located.
- AssertionError
If the header did not pass verification.
- get_frame_rate()[source] [edit on github]¶
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 attempts to extract the sample rate from the header.
- Returns:
- frame_rate
Quantity
Frames per second.
- frame_rate
- get_thread_ids(check=2)[source] [edit on github]¶
Determine the number of threads in the VDIF file.
The file is presumed to be positioned at the start of a header. Usually, it suffices to just seek to the start of the file, but if not, use
find_header
.- Parameters:
- checkint, optional
Number of extra frames to check. Frame sets are scanned until the number of thread IDs found no longer increases for
check
frames.
- Returns:
- thread_idslist
Sorted list of all thread ids encountered in the frames scanned.
- locate_frames(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(edv=None, verify=True)[source] [edit on github]¶
Read a single frame (header plus payload).
- Parameters:
- Returns:
- frame
VDIFFrame
With
.header
and.data
properties that return theVDIFHeader
and data encoded in the frame, respectively.
- frame
- read_frameset(thread_ids=None, edv=None, verify=True)[source] [edit on github]¶
Read a single frame (header plus payload).
- Parameters:
- thread_idslist, optional
The thread ids that should be read. If
None
(default), read all threads.- edvint, optional
The expected extended data version for the VDIF Header. If
None
, use that of the first frame. (Passing it in slightly improves file integrity checking.)- verifybool, optional
Whether to do basic checks of frame integrity. Default:
True
.
- Returns:
- frameset
VDIFFrameSet
With
.headers
and.data
properties that return a list ofVDIFHeader
and the data encoded in the frame set, respectively.
- frameset
- read_header(edv=None, verify=True)[source] [edit on github]¶
Read a single header from the file.
- Parameters:
- Returns:
- header
VDIFHeader
- header
- temporary_offset(offset=None, whence=0) [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. As a convenience, one can pass on the offset to seek to when entering the context manager. Parameters are as forio.IOBase.seek()
.