python数据库编程dbf_python读写dbf文件

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读取遍历dBASE或Xbase文件中的记录。从Python的序列创建DBF文件。

import struct,datetime,decimal,itertools

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('

numfields = (lenheader - 33) // 32

fields = []

for fieldno in xrange(numfields):

name,typ,deci = struct.unpack('<11sc4xBB14x',f.read(32))

name = name.replace('\0','') # eliminate NULs from string

fields.append((name,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,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,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,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('

f.write(hdr)

# field specs

for name,(typ,deci) in itertools.izip(fieldnames,fieldspecs):

name = name.ljust(11,'\x00')

fld = struct.pack('<11sc4xBB14x',name,deci)

f.write(fld)

# terminator

f.write('\r')

# records

for record in records:

f.write(' ') # deletion flag

for (typ,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')

# -------------------------------------------------------

# Example calls

if __name__ == '__main__':

import sys,csv

from cStringIO import StringIO

from operator import itemgetter

# Read a database

filename = '/pydev/databases/orders.dbf'

if len(sys.argv) == 2:

filename = sys.argv[1]

f = open(filename,'rb')

db = list(dbfreader(f))

f.close()

for record in db:

print record

fieldnames,records = db[0],db[1],db[2:]

# Alter the database

del records[4]

records.sort(key=itemgetter(4))

# Remove a field

del fieldnames[0]

del fieldspecs[0]

records = [rec[1:] for rec in records]

# Create a new DBF

f = StringIO()

dbfwriter(f,records)

# Read the data back from the new DBF

print '-' * 20

f.seek(0)

for line in dbfreader(f):

print line

f.close()

# Convert to CSV

print '.' * 20

f = StringIO()

csv.writer(f).writerow(fieldnames)

csv.writer(f).writerows(records)

print f.getvalue()

f.close()

# Example Output

"""

['ORDER_ID','CUSTMR_ID','EMPLOY_ID','ORDER_DATE','ORDER_AMT']

[('C',10,0),('C',11,('D',8,('N',12,2)]

['10005 ','WALNG ','555 ',datetime.date(1995,5,22),Decimal("173.40")]

['10004 ','BMARK ','777 ',18),Decimal("3194.20")]

['10029 ','SAWYH ',6,29),Decimal("97.30")]

['10013 ','RITEB ',2),Decimal("560.40")]

['10024 ','RATTC ','444 ',21),Decimal("2223.50")]

['10018 ',12),Decimal("1076.05")]

['10025 ',23),Decimal("185.80")]

['10038 ','OLDWO ','111 ',7,14),Decimal("863.96")]

['10002 ','MTIME ','333 ',16),Decimal("731.80")]

['10007 ','MORNS ',24),Decimal("1405.00")]

['10026 ',26),Decimal("17.40")]

['10030 ','LILLO ',3),Decimal("909.91")]

['10022 ','LAPLA ',19),Decimal("671.50")]

['10035 ','HIGHG ',11),Decimal("1984.83")]

['10033 ','FOODG ',6),Decimal("3401.32")]

--------------------

['CUSTMR_ID',2)]

['MORNS ',Decimal("17.40")]

['SAWYH ',Decimal("97.30")]

['WALNG ',Decimal("173.40")]

['RATTC ',Decimal("185.80")]

['RITEB ',Decimal("560.40")]

['LAPLA ',Decimal("671.50")]

['MTIME ',Decimal("731.80")]

['OLDWO ',Decimal("863.96")]

['LILLO ',Decimal("909.91")]

['RATTC ',Decimal("1076.05")]

['MORNS ',Decimal("1405.00")]

['HIGHG ',Decimal("1984.83")]

['BMARK ',Decimal("3194.20")]

['FOODG ',Decimal("3401.32")]

....................

CUSTMR_ID,EMPLOY_ID,ORDER_DATE,ORDER_AMT

MORNS,555,1995-06-26,17.40

SAWYH,777,1995-06-29,97.30

WALNG,1995-05-22,173.40

RATTC,444,1995-06-23,185.80

RITEB,1995-06-02,560.40

LAPLA,111,1995-06-19,671.50

MTIME,333,1995-05-16,731.80

OLDWO,1995-07-14,863.96

LILLO,1995-07-03,909.91

RATTC,1995-06-12,1076.05

MORNS,1995-05-24,1405.00

HIGHG,1995-07-11,1984.83

BMARK,1995-05-18,3194.20

FOODG,1995-07-06,3401.32

"""

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