Table data file DBF read and write operations

ImportSYSImportCSVImportstructImportdatetimeImportdecimalImportItertools fromCstringioImportStringio fromoperatorImportItemgetterdefDbfreader (f):"""Returns an iterator to 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's skipped.    File should is opened for binary reads. """    #See DBF format spec at:    #Http://www.pgts.com.au/download/public/xbase.htm#DBF_STRUCTNumrec, Lenheader= Struct.unpack ('<xxxxlh22x', F.read (32)) Numfields= (lenheader-33)//32 Fields= []     forFieldnoinchxrange (numfields): Name, Typ, size, Deci= Struct.unpack ('<11sc4xbb14x', F.read (32)) name= Name.replace (' /',"')#eliminate Nuls from stringFields.Append ((name, Typ, size, deci))yield[Field[0] forFieldinchFields ]yield[Tuple (field[1:]) forFieldinchFields ] Terminator= F.read (1)    assertTerminator = ='\ r'Fields.insert (0, ('Deletionflag','C', 1, 0)) FMT="'. Join (['%ds'% fieldinfo[2] forFieldInfoinchFields ]) Fmtsiz=struct.calcsize (FMT) forIinchxrange (numrec): Record=Struct.unpack (FMT, F.read (fmtsiz))ifRECORD[0]! =' ':            Continue  #deleted recordresult = []         for(Name, Typ, size, deci), valueinchitertools.izip (Fields, record):ifName = ='Deletionflag':                Continue            ifTyp = ="N": Value= Value.replace (' /',"'). Lstrip ()ifValue = ="': Value=0elifDeci:value=Decimal. Decimal (value)Else: Value=int (value)elifTyp = ='D': Y, M, D= Int (value[:4]), int (value[4:6]), int (value[6:8]) value=datetime.date (Y, M, D)elifTyp = ='L': Value= (valueinch 'Yytt'  and 'T')or(Valueinch 'NNFF'  and 'F')or '?'            elifTyp = ='F': Value=Float (value) result.append (value)yieldresultdefDbfwriter (F, FieldNames, Fieldspecs, records):"""Return A string suitable for writing directly to a binary DBF file.    File F should is open for writing in a binary mode.    FieldNames should is no longer than ten characters and not include \x00.            Fieldspecs is in the form (type, size, deci) where type is a 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 are the number of decimal places in the provided decimal object Records can be a It    Erable over the records (sequences of field values). """    #Header Infover = 3 Now=Datetime.datetime.now () yr, Mon, day= now.year-1900, Now.month, Now.day Numrec=Len (Records) Numfields=Len (fieldspecs) Lenheader= Numfields * 32 + 33Lenrecord= SUM (field[1] forFieldinchFIELDSPECS) + 1HDR= Struct.pack ('<bbbblhh20x', ver, yr, Mon, day, Numrec, Lenheader, Lenrecord) f.write (HDR)#Field Specs     forName, (Typ, size, deci)inchItertools.izip (FieldNames, fieldspecs): Name= Name.ljust (11,'\x00') FLD= Struct.pack ('<11sc4xbb14x', Name, Typ, size, Deci) f.write (FLD)#TerminatorF.write ('\ r')    #Records     forRecordinchRecords:f.write (' ')#Deletion flag         for(Typ, size, deci), valueinchItertools.izip (Fieldspecs, record):ifTyp = ="N": Value= str (value). Rjust (Size,' ')            elifTyp = ='D': Value= Value.strftime ('%y%m%d')            elifTyp = ='L': Value=Str (value) [0].upper ()Else: Value= str (value) [: Size].ljust (Size,' ')            assertLen (value) = =size F.write (value)#End of FileF.write ('\x1a')    ################################################################################## #3filename ='e:/update/shp/test.dbf'F= open (filename,'RB') DB=list (Dbfreader (f)) F.close () forRecordinchDB:PrintRecord## # # FieldNames is first row means fieldname,fieldspecs are second row means Fieldtype,records is afterrows means Recor DSFieldNames, fieldspecs, records = Db[0], db[1], db[2:]#Remove a fielddelFieldnames[0]delFieldspecs[0]records= [Rec[1:] forRecinchRecords]#Create a new DBFfilename1 ='e:/update/shp/test1.dbf'F1= Open (filename1,'wb+') Dbfwriter (F1, FieldNames, Fieldspecs, Records)#Read the data back from the new DBFPrint '-'* 50f1.seek (0) forLineinchDbfreader (F1):Printlinef1.close ()#Convert to CSVPrint '.'* 50filename1='E:/update/shp/test1.csv'F1= Open (filename1,'wb+') Csv.writer (F1). Writerow (FieldNames) csv.writer (F1). Writerows (Records)PrintF1.getvalue () f1.close ( )

Table data file DBF read and write operations