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|
"""DBF header definition.
TODO:
- handle encoding of the character fields
(encoding information stored in the DBF header)
"""
"""History (most recent first):
16-sep-2010 [als] fromStream: fix century of the last update field
11-feb-2007 [als] added .ignoreErrors
10-feb-2007 [als] added __getitem__: return field definitions
by field name or field number (zero-based)
04-jul-2006 [als] added export declaration
15-dec-2005 [yc] created
"""
__version__ = "$Revision: 1.6 $"[11:-2]
__date__ = "$Date: 2010/09/16 05:06:39 $"[7:-2]
__all__ = ["DbfHeader"]
import datetime
import io
import struct
import sys
from . import fields
from .utils import getDate
class DbfHeader:
"""Dbf header definition.
For more information about dbf header format visit
`http://www.clicketyclick.dk/databases/xbase/format/dbf.html#DBF_STRUCT`
Examples:
Create an empty dbf header and add some field definitions:
dbfh = DbfHeader()
dbfh.addField(("name", "C", 10))
dbfh.addField(("date", "D"))
dbfh.addField(DbfNumericFieldDef("price", 5, 2))
Create a dbf header with field definitions:
dbfh = DbfHeader([
("name", "C", 10),
("date", "D"),
DbfNumericFieldDef("price", 5, 2),
])
"""
__slots__ = ("signature", "fields", "lastUpdate", "recordLength",
"recordCount", "headerLength", "changed", "_ignore_errors")
# instance construction and initialization methods
def __init__(self, fields=None, headerLength=0, recordLength=0,
recordCount=0, signature=0x03, lastUpdate=None, ignoreErrors=False):
"""Initialize instance.
Arguments:
fields:
a list of field definitions;
recordLength:
size of the records;
headerLength:
size of the header;
recordCount:
number of records stored in DBF;
signature:
version number (aka signature). using 0x03 as a default meaning
"File without DBT". for more information about this field visit
``http://www.clicketyclick.dk/databases/xbase/format/dbf.html#DBF_NOTE_1_TARGET``
lastUpdate:
date of the DBF's update. this could be a string ('yymmdd' or
'yyyymmdd'), timestamp (int or float), datetime/date value,
a sequence (assuming (yyyy, mm, dd, ...)) or an object having
callable ``ticks`` field.
ignoreErrors:
error processing mode for DBF fields (boolean)
"""
self.signature = signature
if fields is None:
self.fields = []
else:
self.fields = list(fields)
self.lastUpdate = getDate(lastUpdate)
self.recordLength = recordLength
self.headerLength = headerLength
self.recordCount = recordCount
self.ignoreErrors = ignoreErrors
# XXX: I'm not sure this is safe to
# initialize `self.changed` in this way
self.changed = bool(self.fields)
# @classmethod
def fromString(cls, string):
"""Return header instance from the string object."""
return cls.fromStream(io.StringIO(str(string)))
fromString = classmethod(fromString)
# @classmethod
def fromStream(cls, stream):
"""Return header object from the stream."""
stream.seek(0)
first_32 = stream.read(32)
if type(first_32) != bytes:
_data = bytes(first_32, sys.getfilesystemencoding())
_data = first_32
(_cnt, _hdrLen, _recLen) = struct.unpack("<I2H", _data[4:12])
# reserved = _data[12:32]
_year = _data[1]
if _year < 80:
# dBase II started at 1980. It is quite unlikely
# that actual last update date is before that year.
_year += 2000
else:
_year += 1900
# create header object
_obj = cls(None, _hdrLen, _recLen, _cnt, _data[0],
(_year, _data[2], _data[3]))
# append field definitions
# position 0 is for the deletion flag
_pos = 1
_data = stream.read(1)
while _data != b'\r':
_data += stream.read(31)
_fld = fields.lookupFor(_data[11]).fromString(_data, _pos)
_obj._addField(_fld)
_pos = _fld.end
_data = stream.read(1)
return _obj
fromStream = classmethod(fromStream)
# properties
year = property(lambda self: self.lastUpdate.year)
month = property(lambda self: self.lastUpdate.month)
day = property(lambda self: self.lastUpdate.day)
def ignoreErrors(self, value):
"""Update `ignoreErrors` flag on self and all fields"""
self._ignore_errors = value = bool(value)
for _field in self.fields:
_field.ignoreErrors = value
ignoreErrors = property(
lambda self: self._ignore_errors,
ignoreErrors,
doc="""Error processing mode for DBF field value conversion
if set, failing field value conversion will return
``INVALID_VALUE`` instead of raising conversion error.
""")
# object representation
def __repr__(self):
_rv = """\
Version (signature): 0x%02x
Last update: %s
Header length: %d
Record length: %d
Record count: %d
FieldName Type Len Dec
""" % (self.signature, self.lastUpdate, self.headerLength,
self.recordLength, self.recordCount)
_rv += "\n".join(
["%10s %4s %3s %3s" % _fld.fieldInfo() for _fld in self.fields]
)
return _rv
# internal methods
def _addField(self, *defs):
"""Internal variant of the `addField` method.
This method doesn't set `self.changed` field to True.
Return value is a length of the appended records.
Note: this method doesn't modify ``recordLength`` and
``headerLength`` fields. Use `addField` instead of this
method if you don't exactly know what you're doing.
"""
# insure we have dbf.DbfFieldDef instances first (instantiation
# from the tuple could raise an error, in such a case I don't
# wanna add any of the definitions -- all will be ignored)
_defs = []
_recordLength = 0
for _def in defs:
if isinstance(_def, fields.DbfFieldDef):
_obj = _def
else:
(_name, _type, _len, _dec) = (tuple(_def) + (None,) * 4)[:4]
_cls = fields.lookupFor(_type)
_obj = _cls(_name, _len, _dec, ignoreErrors=self._ignore_errors)
_recordLength += _obj.length
_defs.append(_obj)
# and now extend field definitions and
# update record length
self.fields += _defs
return _recordLength
# interface methods
def addField(self, *defs):
"""Add field definition to the header.
Examples:
dbfh.addField(
("name", "C", 20),
dbf.DbfCharacterFieldDef("surname", 20),
dbf.DbfDateFieldDef("birthdate"),
("member", "L"),
)
dbfh.addField(("price", "N", 5, 2))
dbfh.addField(dbf.DbfNumericFieldDef("origprice", 5, 2))
"""
_oldLen = self.recordLength
self.recordLength += self._addField(*defs)
if not _oldLen:
self.recordLength += 1
# XXX: may be just use:
# self.recordeLength += self._addField(*defs) + bool(not _oldLen)
# recalculate headerLength
self.headerLength = 32 + (32 * len(self.fields)) + 1
self.changed = True
def write(self, stream):
"""Encode and write header to the stream."""
stream.seek(0)
stream.write(self.toString())
fields = [_fld.toString() for _fld in self.fields]
stream.write(''.join(fields).encode(sys.getfilesystemencoding()))
stream.write(b'\x0D') # cr at end of all header data
self.changed = False
def toString(self):
"""Returned 32 chars length string with encoded header."""
return struct.pack("<4BI2H",
self.signature,
self.year - 1900,
self.month,
self.day,
self.recordCount,
self.headerLength,
self.recordLength) + (b'\x00' * 20)
# TODO: figure out if bytes(utf-8) is correct here.
def setCurrentDate(self):
"""Update ``self.lastUpdate`` field with current date value."""
self.lastUpdate = datetime.date.today()
def __getitem__(self, item):
"""Return a field definition by numeric index or name string"""
if isinstance(item, str):
_name = item.upper()
for _field in self.fields:
if _field.name == _name:
return _field
else:
raise KeyError(item)
else:
# item must be field index
return self.fields[item]
# vim: et sts=4 sw=4 :
|
