83 lines
2.1 KiB
Python
83 lines
2.1 KiB
Python
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#!/usr/bin/env python
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"""
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This module contains a generic parser for fixed-width files. It operates
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similar to Python's built-in CSV reader.
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"""
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from collections import OrderedDict, namedtuple
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import six
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Field = namedtuple('Field', ['name', 'start', 'length'])
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class Reader(six.Iterator):
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"""
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Reads a fixed-width file using a column schema in CSV format.
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This works almost exactly like Python's built-in CSV reader.
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Schemas must be in the "ffs" format, with :code:`column`, :code:`start`,
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and :code:`length` columns. There is a repository of such schemas
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maintained at `wireservice/ffs <https://github.com/wireservice/ffs>`_.
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"""
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def __init__(self, f, schema_f):
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from agate import csv
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self.file = f
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self.fields = []
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reader = csv.reader(schema_f)
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header = next(reader)
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if header != ['column', 'start', 'length']:
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raise ValueError('Schema must contain exactly three columns: "column", "start", and "length".')
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for row in reader:
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self.fields.append(Field(row[0], int(row[1]), int(row[2])))
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def __iter__(self):
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return self
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def __next__(self):
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line = next(self.file)
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values = []
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for field in self.fields:
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values.append(line[field.start:field.start + field.length].strip())
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return values
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@property
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def fieldnames(self):
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"""
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The names of the columns read from the schema.
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"""
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return [field.name for field in self.fields]
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class DictReader(Reader):
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"""
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A fixed-width reader that returns :class:`collections.OrderedDict` rather
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than a list.
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"""
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def __next__(self):
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line = next(self.file)
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values = OrderedDict()
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for field in self.fields:
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values[field.name] = line[field.start:field.start + field.length].strip()
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return values
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def reader(*args, **kwargs):
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"""
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A wrapper around :class:`.fixed.Reader`, so that it can be used in the same
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way as a normal CSV reader.
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"""
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return Reader(*args, **kwargs)
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