表数据文件DBF的读取和写入操作

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()

 

表数据文件DBF的读取和写入操作

标签：