Jan-31-2021, 08:43 PM
I don't know if this is the best solution, but it does appear to work fairly well for the header. This is the base class for binary files with headers.
I am looking at numpy.rot90, are there other tools that do this kind of thing? Other choices are to call an external C function to do the rotation.
"""Binfile. A binary file with a header."""
def valid_key(key, valid_keys=None):
"""Validate key against a list of valid keys. Return True if key in list"""
if valid_keys is None:
return True
for k in valid_keys:
if key == k:
return True
return False
class BinFile():
"""Class to read and write binary file format"""
def __init__(self, filename=None, mode=None):
self.filename = filename
self.mode = mode
self.file = None
self.header = {}
def __enter__(self):
"""Context manager enter. Do open(filename, mode)"""
self.open(self.filename, self.mode)
return self
def __exit__(self, *args):
"""Context manager exit. Closes file if open"""
self.close()
def open(self, filename, mode):
"""Open file for reading ("r") or writing ("w")"""
if mode in ('r', 'rb'):
self.file = open(filename, 'rb')
self.read_header()
elif mode in ('w', 'wb'):
self.file = open(filename, 'wb')
self.write_header() # Can call write_header again if changes are requried
else:
self.file = None
raise ValueError(f'Invalid mode {mode} for open')
def close(self):
"""Close file"""
self.file.close()
def read_header(self):
"""Read header from a file. Looks for first "key" that contains a
non-ascii character. Override in subclass
"""
self.file.seek(0)
self.header = {}
while True:
key, value = self.read_header_line()
if key is None:
self.file.seek(len(self.header)*128)
break
self.header[key] = value
def write_header(self):
"""Write header to a file"""
self.file.seek(0)
for key, value in self.header.items():
self.write_header_line(key, value)
def read_header_line(self, valid_keys=None):
"""Read a line from the header. Return key and value.
Use optional valid_keys to validate header key.
"""
try:
line = self.file.read(128).decode('ascii')
except UnicodeDecodeError:
return None, None
if len(line) < 128:
return None, None
key = line[:32].strip()
value = line[32:].strip()
if valid_keys is not None:
if not valid_key(key, valid_keys):
raise ValueError(f'Unexpected key {key}')
return key, value
def write_header_line(self, key, value=None):
"""Write a header line to a file"""
if value is None:
value = self.header[key]
self.file.write(bytes(f'{key:\0<32}{value:\0<96}', 'utf-8'))Now I am starting to look at the time history part of the file. Let's say I have 2 channels , call them x and y, each with 5 data points. The data in the file will look like this:Quote:x0, y0, x1, y1, x2, y2, x3, y3, x4, y4When I use the data I need it to be arranged by channel.
Quote:x0, x1, x2, x3, x4, y0, y1, y2, y3, y4A real file will probably be 8 channels instead of 2, and 10,000 data points per channel instead of 5. There is also a hard time limit on reading from the file and rotating the data (tens of milliseconds), so I need this to be fast.
I am looking at numpy.rot90, are there other tools that do this kind of thing? Other choices are to call an external C function to do the rotation.