5.1 Binary File Handling.pdf

Binary file handling notes

1. Binary file operations
•Allbinaryfilesfollowaspecificformat.Wecanopensomebinaryfilesinthenormaltext
editorbutwecan’treadthecontentpresentinsidethefile.That’sbecauseallthebinary
fileswillbeencodedinthebinaryformat,whichcanbeunderstoodonlybyacomputer
oramachine.
•In binary files, there is no delimiter to end a line. Since they are directly in the form of
binary, hence there is no need to translate them. That’s why these files are easy and fast
in working.
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2. Binary file operations
•Ifwewanttowriteastructuresuchaslistordictionarytoafileandreadit
subsequently,weneedtousethePythonmodulepickle.
•Picklingistheprocessofconvertingstructuretoabytestreambeforewritingtoa
file
•Whilereadingthecontentoffile,areverseprocesscalledUnpicklingisusedto
convertthebytestreambacktotheoriginalformat.
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3. Steps to perform binary file operations
•First we need to import the module called pickle.
•This module provides 2 main functions:
•dump() : to write the object in file which is loaded in binary mode
•Syntax : dump(object_to_write, filehandle)
•load() : dumped data can be read from file using load() i.e. it is used to read
object from pickle file.
•Syntax:object = load(filehandle)
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4. Program to write structure, list in the binary file
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5. Program to write structure, dictionary in the binary file
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6. Program to read list items from the binary file
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7. Program to read dictionary items from the binary file
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8. Insert/Append a Record in Binary File
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Asshownintheaboveprogram,insertingandadding
recordinstudentfilebeginswithimportingpicklemodule.
Then,iteratingforthenumberofrecordstobeaddedis
doneusingwhileloop.Inputisacceptedfromtheuserfor
rollnumber,nameandmarks.Thesefetchedvaluesare
savedasalisttobeappended.Oncetherecordiscreated,
itisappendedtothebinaryfile“student”usingthedump()
method,whichwritestheobjectintotheopenedfile.

10. Reading a record from a binary file
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11. Reading a record from a binary file
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•Theaboveprogramdealswithreadingthecontentsfrombinaryfile
studentusingload()methodofpicklemodule.Itisusedtoreadthe
objectfromtheopenedfile.Thesyntaxforthisisgivenbythe
statement—
object=pickle.load(file)
•Oncethecontentsareread,itgetsstoredinsidetheobject,rec.All
thedataoftherespectivefieldsfromthisobjectisheldinthe
respectivevariables,roll,nameandmarksandarefinallydisplayedas
theoutput.

12. Program to search a record from the binary file
"student.dat" on the basis of roll number.
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13. Updating a record in a binary file
•Firstweneedtosearchtherecordfromthebinaryfile,whichistobeupdated.
•Oncetherecordisfound,thefilepointerismovedtothebeginningofthefile
usingseek(0)statement,andthenthechangednameiswrittentothefileandthe
recordisupdated.
•seek()methodisusedforrandomaccesstothefile.
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14. Updating a record in the file requires roll number to be
fetched from the user whose name is to beupdated
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15. Display Record (Formatted Output)
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16. Display Record (Formatted Output)
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17. Searching in Binary File(Search Form)
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18. Finding Number of Record in Binary File
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19. Deleting a record in a binary file
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Existing Records in File

20. Deleting a record in a binary file
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21. RANDOM ACCESS IN FILES
•Pythonallowrandomaccessofthedataaswellusingbuilt-inmethodsseek()andtell().
•seek()—seek() function is used to change the position of the file handle (file pointer) to
a given specific position.
seek() can be done in two ways:
• Absolute Positioning
• Relative Positioning
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22. ABSOLUTE POSITIONING
•The syntax for seek() is—
•f.seek(file_location)#wherefisthefilepointer
•For example
•f.seek(20)
•This statement shall move the file pointer to 20th byte in the file no matter where
you are.
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23. RELATIVE POSITIONING
•Relative referencing/positioning has two arguments, offset and the position from
which it has to traverse.
•The syntax for relative referencing is: f.seek(offset, from_what)
•The "from_what" argument can have any of the three values:
•0: sets the reference point at the beginning of the file, which is by default.
•1: sets the reference point at the current file position.
•2: sets the reference point at the end of the file
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24. RELATIVE POSITIONING
•For example,
•f.seek(–10,1) from current position, move 10 bytes backward
•f.seek(10,1) from current position, move 10 bytes forward
•f.seek(–20,1) from current position, move 20 bytes backward
•f.seek(10,0) from beginning of file, move 10 bytes forward
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25. RANDOM ACCESS IN FILES
•tell()—tell() returns the current position of the file read/write pointer within the
file.
•Its syntax is:
f.tell() #where f is file pointer
•When you open a file in reading/writing mode, the file pointer rests at 0th byte.
•When you open a file in append mode, the file pointer rests at last byte.
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