จากครั้งก่อนเรื่อง adodb: ​กับ​ดักข้อมูล ที่ได้นำเอาโมดูล DBF Reader จากเว็บของคุณ Yusdi Santoso มาทดลองใช้งาน

เมื่อได้นำมาใช้จริง สำหรับไฟล์ dbf ของ Visual Foxpro สามารถใช้ได้ผลดีพอควร แต่สำหรับ dbf เก่า ๆ ที่เป็นของ Foxpro for Dos นั้น ปรากฎว่าไม่สามารถอ่านได้

อีกเรื่องนึงคือเรื่องชื่อไฟล์ในลินุกซ์ เมื่อใช้งานผ่าน samba (เมานต์แบบ cifs) แล้ว เข้าใจว่าไม่สามารถควบคุมได้ บางครั้งปรากฎเป็นตัวใหญ่หมด บางครั้งออกมาเป็นชื่อไฟล์ตัวใหญ่แต่นามสกุลตัวเล็ก หรือกลับกัน เราจึงมาปรับปรุงในส่วนนี้ด้วย

ได้ออกมาเป็นซอร์สไฟล์ดังนี้ครับ
$ vi dbf.py

#!/usr/bin/env python
"""
This is a DBF reader which reads Visual Fox Pro DBF format with Memo field.

Usage:
    rec = readDbf('test.dbf')
    for line in rec:
        print line['name']

@author Yusdi Santoso
@date 13/07/2007
"""
import struct
import os, os.path
import sys
import csv
import tempfile
import ConfigParser

class Dbase:
    def __init__(self):
        self.fdb = None
        self.fmemo = None
        self.db_data = None
        self.memo_data = None
        self.fields = None
        self.num_records = 0
        self.header = None
        self.memo_file = ''
        self.memo_header = None
        self.memo_block_size = 0
        self.memo_header_len = 0

    def _drop_after_NULL(self, txt):
        for i in range(0, len(txt)):
            if ord(struct.unpack('c', txt[i])​[0])==0:
                return txt[:i]
        return txt 

    def _reverse_endian(self, num):
        if not len(num):
            return 0
        #OLD CODE
        #val = struct.unpack('<L', num)
        #val = struct.pack('>L', val[0])
        #val = struct.unpack('>L', val)
        #return val[0]
        #wd's IMP: IMPROVE READING OLD FOXPRO MEMO
        try:       #VFP DBF: BINARY 4 BYTES MEMO FIELD REF
            val = struct.unpack('<L', num)
            val = struct.pack('>L', val[0])
            val = struct.unpack('>L', val)
            return val[0]
        except:    #OLD FOXPRO DBF: STRING 10 BYTES MEMO FIELD REF
            val = long('0'+num.strip())
            return val
    def _assign_ids(self, lst, ids):
        result = {}
        idx = 0
        for item in lst:
            id = ids[idx]
            result[id] = item
            idx += 1
        return result

    def open(self, db_name):
        filesize = os.path.getsize(db_name)
        if filesize <= 68:
            raise IOError, 'The file is not large enough to be a dbf file'

        self.fdb = open(db_name, 'rb')

        self.memo_file = ''
        #OLD CODE
        #if os.path.isfile(db_name[0:-1] + 't'):
        #    self.memo_file = db_name[0:-1] + 't'
        #elif os.path.isfile(db_name[0:-3] + 'fpt'):
        #    self.memo_file = db_name[0:-3] + 'fpt'
        
        #wd's IMP: SOLVE MISMATCHED UPPER/LOWER FILENAME AND EXTENSION
        basename = os.path.basename(db_name)
        dirname = os.path.dirname(os.path.join('.',db_name))
        allfile=[i for i in os.listdir(dirname) if i[:-4].lower()==basename[:-4].lower()]
        for i in allfile:
            if i[:-1].lower()==basename[:-1].lower() and i[-1].lower()=='t':
                self.memo_file = os.path.join(dirname, i)
            elif i[:-3].lower()==basename[:-3].lower() and i[-3:].lower()=='fpt':
                self.memo_file = os.path.join(dirname, i)
        if self.memo_file:    
            #Read memo file
            self.fmemo = open(self.memo_file, 'rb')
            self.memo_data = self.fmemo.read()
            self.memo_header = self._assign_ids(struct.unpack('>6x1H', self.memo_data[:8]), ['Block size'])
            block_size = self.memo_header['Block size']
            if not block_size:
                block_size = 512
            self.memo_block_size = block_size
            self.memo_header_len = block_size
            memo_size = os.path.getsize(self.memo_file)

        #Start reading data file
        data = self.fdb.read(32)
        self.header = self._assign_ids(struct.unpack('<B 3B L 2H 20x', data), ['id', 'Year', 'Month', 'Day', '# of Records', 'Header Size', 'Record Size'])
        self.header['id'] = hex(self.header['id'])

        self.num_records = self.header['# of Records']
        data = self.fdb.read(self.header['Header Size']-34)
        self.fields = {}
        x = 0
        header_pattern = '<11s c 4x B B 14x'
        ids = ['Field Name', 'Field Type', 'Field Length', 'Field Precision']
        pattern_len = 32
        for offset in range(0, len(data), 32):
            if ord(data[offset])==0x0d:
                break
            x += 1
            data_subset = data[offset: offset+pattern_len]
            if len(data_subset) < pattern_len:
                data_subset += ' '*(pattern_len-len(data_subset))
            self.fields[x] = self._assign_ids(struct.unpack(header_pattern, data_subset), ids)
            self.fields[x]​['Field Name'] = self._drop_after_NULL(self.fields[x]​['Field Name'])

        self.fdb.read(3)
        if self.header['# of Records']:
            data_size = (self.header['# of Records'] * self.header['Record Size']) - 1
            self.db_data = self.fdb.read(data_size)
        else:
            self.db_data = ''
        self.row_format = '<'
        self.row_ids = []
        self.row_len = 0
        for key in self.fields:
            field = self.fields[key]
            self.row_format += '%ds ' % (field['Field Length'])
            self.row_ids.append(field['Field Name'])
            self.row_len += field['Field Length']

    def close(self):
        if self.fdb:
            self.fdb.close()
        if self.fmemo:
            self.fmemo.close()

    def get_numrecords(self):
        return self.num_records

    def get_record_with_names(self, rec_no):
        """
        This function accept record number from 0 to N-1
        """
        if rec_no < 0 or rec_no > self.num_records:
            raise Exception, 'Unable to extract data outside the range' 

        offset = self.header['Record Size'] * rec_no
        data = self.db_data[offset:offset+self.row_len]
        record = self._assign_ids(struct.unpack(self.row_format, data), self.row_ids)

        if self.memo_file:
            for key in self.fields:
                field = self.fields[key]
                f_type = field['Field Type']
                f_name = field['Field Name']
                c_data = record[f_name]

                if f_type=='M' or f_type=='G' or f_type=='B' or f_type=='P':
                    c_data = self._reverse_endian(c_data)
                    if c_data:
                        record[f_name] = self.read_memo(c_data-1).strip()
                else:
                    record[f_name] = c_data.strip()
        return record

    def read_memo_record(self, num, in_length):
        """
        Read the record of given number. The second parameter is the length of
        the record to read. It can be undefined, meaning read the whole record,
        and it can be negative, meaning at most the length
        """
        if in_length < 0:
            in_length = -self.memo_block_size

        offset = self.memo_header_len + num * self.memo_block_size
        self.fmemo.seek(offset)
        if in_length<0:
            in_length = -in_length
        if in_length==0:
            return ''
        return self.fmemo.read(in_length)    
    
    def read_memo(self, num):
        result = ''
        buffer = self.read_memo_record(num, -1)
        if len(buffer)<=0:
            return ''
        length = struct.unpack('>L', buffer[4:4+4])​[0] + 8

        block_size = self.memo_block_size
        if length < block_size:
            return buffer[8:length]
        rest_length = length - block_size
        rest_data = self.read_memo_record(num+1, rest_length)
        if len(rest_data)<=0:
            return ''
        return buffer[8:] + rest_data

def readDbf(filename):
    """
    Read the DBF file specified by the filename and 
    return the records as a list of dictionary.
    @param filename File name of the DBF
    @return List of rows
    """
    db = Dbase()
    db.open(filename)
    num = db.get_numrecords()
    rec = []
    for i in range(0, num):
        record = db.get_record_with_names(i)
        rec.append(record)    
    db.close()
    return  rec

if __name__=='__main__':
    rec = readDbf('dbf/sptable.dbf')
    for line in rec:
        print '%s %s' % (line['GENUS'].strip(), line['SPECIES'].strip())

ผลการปรับปรุงปรากฎว่าใช้งานได้ดีพอควรครับ