表数据文件DBF的读取和写入操作

古城微笑少年丶 2022-03-28 15:48 267阅读 0赞

import sys
    import csv
    import struct
    import datetime
    import decimal
    import itertools
    from cStringIO import StringIO
    from operator import itemgetter
    
    def dbfreader(f):
        """Returns an iterator over records in a Xbase DBF file.
    
        The first row returned contains the field names.
        The second row contains field specs: (type, size, decimal places).
        Subsequent rows contain the data records.
        If a record is marked as deleted, it is skipped.
    
        File should be opened for binary reads.
    
        """
        # See DBF format spec at:
        #     http://www.pgts.com.au/download/public/xbase.htm#DBF_STRUCT
    
        numrec, lenheader = struct.unpack('<xxxxLH22x', f.read(32))
        numfields = (lenheader - 33) // 32
    
        fields = []
        for fieldno in xrange(numfields):
            name, typ, size, deci = struct.unpack('<11sc4xBB14x', f.read(32))
            name = name.replace('\0', '')  # eliminate NULs from string
            fields.append((name, typ, size, deci))
        yield [field[0] for field in fields]
        yield [tuple(field[1:]) for field in fields]
    
        terminator = f.read(1)
        assert terminator == '\r'
    
        fields.insert(0, ('DeletionFlag', 'C', 1, 0))
        fmt = ''.join(['%ds' % fieldinfo[2] for fieldinfo in fields])
        fmtsiz = struct.calcsize(fmt)
        for i in xrange(numrec):
            record = struct.unpack(fmt, f.read(fmtsiz))
            if record[0] != ' ':
                continue  # deleted record
            result = []
            for (name, typ, size, deci), value in itertools.izip(fields, record):
                if name == 'DeletionFlag':
                    continue
                if typ == "N":
                    value = value.replace('\0', '').lstrip()
                    if value == '':
                        value = 0
                    elif deci:
                        value = decimal.Decimal(value)
                    else:
                        value = int(value)
                elif typ == 'D':
                    y, m, d = int(value[:4]), int(value[4:6]), int(value[6:8])
                    value = datetime.date(y, m, d)
                elif typ == 'L':
                    value = (value in 'YyTt' and 'T') or (value in 'NnFf' and 'F') or '?'
                elif typ == 'F':
                    value = float(value)
                result.append(value)
            yield result
    
    
    def dbfwriter(f, fieldnames, fieldspecs, records):
        """ Return a string suitable for writing directly to a binary dbf file.
    
        File f should be open for writing in a binary mode.
    
        Fieldnames should be no longer than ten characters and not include \x00.
        Fieldspecs are in the form (type, size, deci) where
            type is one of:
                C for ascii character data
                M for ascii character memo data (real memo fields not supported)
                D for datetime objects
                N for ints or decimal objects
                L for logical values 'T', 'F', or '?'
            size is the field width
            deci is the number of decimal places in the provided decimal object
        Records can be an iterable over the records (sequences of field values).
    
        """
        # header info
        ver = 3
        now = datetime.datetime.now()
        yr, mon, day = now.year - 1900, now.month, now.day
        numrec = len(records)
        numfields = len(fieldspecs)
        lenheader = numfields * 32 + 33
        lenrecord = sum(field[1] for field in fieldspecs) + 1
        hdr = struct.pack('<BBBBLHH20x', ver, yr, mon, day, numrec, lenheader, lenrecord)
        f.write(hdr)
    
        # field specs
        for name, (typ, size, deci) in itertools.izip(fieldnames, fieldspecs):
            name = name.ljust(11, '\x00')
            fld = struct.pack('<11sc4xBB14x', name, typ, size, deci)
            f.write(fld)
    
        # terminator
        f.write('\r')
    
        # records
        for record in records:
            f.write(' ')  # deletion flag
            for (typ, size, deci), value in itertools.izip(fieldspecs, record):
                if typ == "N":
                    value = str(value).rjust(size, ' ')
                elif typ == 'D':
                    value = value.strftime('%Y%m%d')
                elif typ == 'L':
                    value = str(value)[0].upper()
                else:
                    value = str(value)[:size].ljust(size, ' ')
                assert len(value) == size
                f.write(value)
    
        # End of file
        f.write('\x1A')
    
        ###################################################################################3
    filename = 'e:/update/shp/test.dbf'
    f = open(filename, 'rb')
    db = list(dbfreader(f))
    f.close()
    for record in db:
        print record
    ##### fieldnames is first row means fieldname,fieldspecs is second row means fieldType,records is afterRows means records
    fieldnames, fieldspecs, records = db[0], db[1], db[2:]
    
    
    # Remove a field
    del fieldnames[0]
    del fieldspecs[0]
    records = [rec[1:] for rec in records]
    
    # Create a new DBF
    filename1 ='e:/update/shp/test1.dbf'
    f1 = open(filename1, 'wb+')
    dbfwriter(f1, fieldnames, fieldspecs, records)
    
    # Read the data back from the new DBF
    print '-' * 50
    f1.seek(0)
    for line in dbfreader(f1):
        print line
    f1.close()
    
    # Convert to CSV
    print '.' * 50
    filename1 ='e:/update/shp/test1.csv'
    f1 = open(filename1, 'wb+')
    csv.writer(f1).writerow(fieldnames)
    csv.writer(f1).writerows(records)
    print f1.getvalue()
    f1.close()