To efficiently parse fixed-width files, one may consider leveraging Python's struct module. This approach leverages C for improved speed, as demonstrated in the following example:
<code class="python">import struct
fieldwidths = (2, -10, 24)
fmtstring = ' '.join('{}{}'.format(abs(fw), 'x' if fw < 0 else 's') for fw in fieldwidths)
unpack = struct.Struct(fmtstring).unpack_from # Alias.
parse = lambda line: tuple(s.decode() for s in unpack(line.encode()))
line = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789\n'
fields = parse(line)
print('fields: {}'.format(fields))</code>Alternatively, string slicing can be employed. To enhance efficiency, consider defining a lambda function that compiles slices at runtime, as seen in the below optimized version:
<code class="python">def make_parser(fieldwidths):
cuts = tuple(cut for cut in accumulate(abs(fw) for fw in fieldwidths))
pads = tuple(fw < 0 for fw in fieldwidths) # bool flags for padding fields
flds = tuple(zip_longest(pads, (0,) + cuts, cuts))[:-1] # ignore final one
slcs = ', '.join('line[{}:{}]'.format(i, j) for pad, i, j in flds if not pad)
parse = eval('lambda line: ({})\n'.format(slcs)) # Create and compile source code.
# Optional informational function attributes.
parse.size = sum(abs(fw) for fw in fieldwidths)
parse.fmtstring = ' '.join('{}{}'.format(abs(fw), 'x' if fw < 0 else 's')
for fw in fieldwidths)
return parse</code>The above is the detailed content of How to Optimize Fixed Width File Parsing in Python?. For more information, please follow other related articles on the PHP Chinese website!
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