Chapter 08 data file handling

CHAPTER - 08 DATA FILE HANDLING

Unit I Programming and Computational Thinking (PCT-2) (80 Theory + 70 Practical) DCSc & Engg, PGDCA,ADCA,MCA.MSc(IT),Mtech(IT),MPhil (Comp. Sci) Department of Computer Science, Sainik School Amaravathinagar Cell No: 9431453730 Praveen M Jigajinni Prepared by Courtesy CBSE Class XII

LEARNING OUTCOMES After going through the chapter, student will be able to: Understand the importance of data file for permanent storage of data. Understand how standard Input/Output function work. Distinguish between text and binary file Open and close a file ( text and binary) Read and write data in file Write programs that manipulate data file(s

INTRODUCTION – DATA FILES A file (i.e. data file) is a named place on the disk where a sequence of related data is stored. In python files are simply stream of data, so the structure of data is not stored in the file, along with data.

Basic operations performed on a data file are: 1. Naming a file 2. Opening a file 3. Reading data from the file 4. Writing data in the file 5. Closing a file BASIC OPERATIONS ON FILE

Using these basic operations, we can process file in many ways, such as 1. CREATING A FILE 2. TRAVERSING A FILE FOR DISPLAYING THE DATA ON SCREEN 3. APPENDING DATA IN FILE 4. INSERTING DATA IN FILE Contd.. next FILE PROCESSING

INTRODUCTION – DATA FILES 6. CREATE A COPY OF FILE 7. UPDATING DATA IN THE FILE … etc 5. DELETING DATA FROM FILE

TYPES OF FILES Python allow us to create and manage two types of file 1. TEXT FILE 2. BINARY FILE

What is Text File? A text file is usually considered as sequence of lines. Line is a sequence of characters (ASCII or UNICODE), stored on permanent storage media. The default character coding in python is ASCII each line is terminated by a special character, known as End of Line (EOL). At the lowest level, text file will be collection of bytes. Text files are stored in human readable form and they can also be created using any text editor. 1. TEXT FILE

What is Binary File? A binary file contains arbitrary binary data i.e. numbers stored in the file, can be used for numerical operation(s). So when we work on binary file, we have to interpret the raw bit pattern(s) read from the file into correct type of data in our program. In the case of binary file it is extremely important that we interpret the correct data type while reading the file. Python provides special module(s) for encoding and decoding of data for binary file. 2. BINARY FILE

OPENING AND CLOSING FILES To handle data files in python, we need to have a file object. Object can be created by using open() function or file() function. To work on file, first thing we do is open it. This is done by using built in function open(). Syntax of open() function is file_object = open(filename [, access_mode] [,buffering])

OPENING AND CLOSING FILES open() requires three arguments to work, first one ( filename ) is the name of the file on secondary storage media, which can be string constant or a variable. The name can include the description of path, in case, the file does not reside in the same folder / directory in which we are working The second parameter (access_mode) describes how file will be used throughout the program. This is an optional parameter and the default access_mode is reading.

OPENING AND CLOSING FILES The third parameter (buffering) is for specifying how much is read from the file in one read. Finally, The function will return an object of file type using which we will manipulate the file, in our program. When we work with file(s), a buffer (area in memory where data is temporarily stored before being written to file), is automatically associated with file when we open the file.

OPENING AND CLOSING FILES While writing the content in the file, first it goes to buffer and once the buffer is full, data is written to the file. Also when file is closed, any unsaved data is transferred to file. flush() function is used to force transfer of data from buffer to file

FILE ACCESS MODES MODE File Opens in r Text File Read Mode rb Binary File Read Mode These are the default modes. The file pointer is placed at the beginning for reading purpose, when we open a file in this mode.

FILE ACCESS MODES MODE File Opens in r+ Text File Read & Write Mode rb+ Binary File Read Write Mode w Text file write mode wb Text and Binary File Write Mode w+ Text File Read and Write Mode wb+ Text and Binary File Read and Write Mode a Appends text file at the end of file, if file does not exists it creates the file.

FILE ACCESS MODES MODE File Opens in ab Appends both text and binary files at the end of file, if file does not exists it creates the file. a+ Text file appending and reading. ab+ Text and Binary file for appending and reading.

FILE ACCESS MODES - EXAMPLE For Ex: f=open(“notes.txt”, ‘r’) This is the default mode for a file. notes.txt is a text file and is opened in read mode only.

FILE ACCESS MODES - EXAMPLE For Ex: f=open(“notes.txt”, ‘r+’) notes.txt is a text file and is opened in read and write mode.

FILE ACCESS MODES - EXAMPLE For Ex: f=open(“tests.dat ”, ‘rb’) tests.dat is a binary file and is opened in read only mode.

FILE ACCESS MODES - EXAMPLE For Ex: f=open(“tests.dat”, ‘rb+’) tests.dat is binary file and is opened in both modes that is reading and writing.

FILE ACCESS MODES - EXAMPLE For Ex: f=open(“tests.dat”, ‘ab+’) tests.dat is binary file and is opened in both modes that is reading and appending.

close FUNCTION fileobject. close() will be used to close the file object, once we have finished working on it. The method will free up all the system resources used by the file, this means that once file is closed, we will not be able to use the file object any more. For example: f.close()

FILE READING METHODS PYTHON PROGRAM A Program reads a text/binary file from hard disk. File acts like an input to a program.

FILE READING METHODS Followings are the methods to read a data from the file. 1. readline() METHOD 2. readlines() METHOD 3. read() METHOD

readline() METHOD readline() will return a line read, as a string from the file. First call to function will return first line, second call next line and so on. It's syntax is, fileobject.readline()

readline() EXAMPLE First create a text file and save under filename notes.txt

readline() EXAMPLE O/P readline() will return only one line from a file, but notes.txt file containing three lines of text

readlines() METHOD readlines()can be used to read the entire content of the file. You need to be careful while using it w.r.t. size of memory required before using the function. The method will return a list of strings, each separated by n. An example of reading entire data of file in list is: It's syntax is, fileobject.readlines() as it returns a list, which can then be used for manipulation.

readlines() EXAMPLE The readlines() method will return a list of strings, each separated by n

read() METHOD The read() method is used to read entire file The syntax is: fileobject.read() For example Contd…

read() METHOD EXAMPLE O/P The read() method will return entire file.

read(size) METHOD read() can be used to read specific size string from file. This function also returns a string read from the file. Syntax of read() function is: fileobject.read([size]) For Example: f.read(1) will read single byte or character from a file.

read(size) METHOD EXAMPLE f.read(1) will read single byte or character from a file and assigns to x.

WRITING METHODS PYTHON PROGRAM A Program writes into a text/binary file from hard disk.

WRITING METHODS 1. write () METHOD 2. writelines() METHOD

1. write () METHOD For sending data in file, i.e. to create / write in the file, write() and writelines() methods can be used. write() method takes a string ( as parameter ) and writes it in the file. For storing data with end of line character, you will have to add n character to end of the string

1. write () METHOD EXAMPLE Use ‘a’ in open function to append or add the information to the file. ‘a+’ to add as well as read the file.

1. write () METHOD EXAMPLE if you execute the program n times, the file is opened in w mode meaning it deletes content of file and writes fresh every time you run.

1. write () METHOD EXAMPLE O/P if you execute the program n times, the file is opened in w mode meaning it deletes content of file and writes fresh every time you run.

1. write () METHOD EXAMPLE 2 now content of test1.txt is changed because the file is opened in w mode and this mode deletes all content and writes fresh if file exists. n write to next line. If not used it writes on the same line.

1. write () METHOD EXAMPLE 2 So test1.txt is already exists in harddisk and it deletes all content and writes fresh. If file not found it creates new file.

2. writelines() METHOD For writing a string at a time, we use write() method, it can't be used for writing a list, tuple etc. into a file. Sequence data type can be written using writelines() method in the file. It's not that, we can't write a string using writelines() method. It's syntax is: fileobject.writelines(seq)

2. writelines() METHOD So, whenever we have to write a sequence of string / data type, we will use writelines(), instead of write(). Example: f = open('test2.txt','w') str = 'hello world.n this is my first file handling program.n I am using python language" f.writelines(str) f.close()

RANDOM ACCESS METHODS All reading and writing functions discussed till now, work sequentially in the file. To access the contents of file randomly – following methods are use. seek method tell method

seek()method can be used to position the file object at particular place in the file. It's syntax is : fileobject.seek(offset [, from_what]) here offset is used to calculate the position of fileobject in the file in bytes. Offset is added to from_what (reference point) to get the position. Following is the list of from_what values: seek method

Value reference point 0 beginning of the file 1 current position of file 2 end of file default value of from_what is 0, i.e. beginning of the file. seek method

seek method f.seek(7) keeps file pointer at reads the file content from 8th position onwards to till EOF.

seek method Results: - So 8th position onwards to till EOF.

Reading according to size In the input function if you specify the number of bytes that many number of bytes can be fetched and assigned to an identifier.

Reading according to size f.read(1) will read single byte/ character starting from byte number 8. hence byte number 8 is P so one character/byte is fetched and assigned to f_data identifier.

Reading according to size f.read(2) - will read 2 chars/bytes f.read(4) - will read 4 chars/bytes and so on..

tell() method returns an integer giving the current position of object in the file. The integer returned specifies the number of bytes from the beginning of the file till the current position of file object. It's syntax is fileobject.tell() tell method

tell() method tell() method returns an integer and assigned to pos variable. It is the current position from the beginning of file.

CONTENT OF BINARY FILE Content of binary file which is in codes.

READING BINARY FILES TROUGH PROGRAM

PICKELING AND UNPICKLING USING PICKEL MODULE

PICKELING AND UNPICKLING USING PICKEL MODULE Use the python module pickle for structured data such as list or directory to a file. PICKLING refers to the process of converting the structure to a byte stream before writing to a file. while reading the contents of the file, a reverse process called UNPICKLING is used to convert the byte stream back to the original structure.

PICKELING AND UNPICKLING USING PICKEL MODULE First we need to import the module, It provides two main methods for the purpose:- 1) dump() method 2) load() method

pickle.dump() Method Use pickle.dump() method to write the object in file which is opened in binary access mode. Syntax of dump method is: dump(object,fileobject)

pickle.dump() Method # A program to write list sequence in a binary file

pickle.dump() Method Once you try to open list.dat file in python editor to see the content python generates decoding error.

pickle.load() Method pickle.load() method is used to read the binary file.

DIFFERENCE BETWEEN TEXT FILES AND BINARY FILES

DIFFERENCE BETWEEN TEXT FILESAND BINARY FILES

DIFFERENCE BETWEEN TEXT FILESAND BINARY FILES Text Files Binary Files 1. Text Files are sequential files 1. A Binary file contain arbitrary binary data 2. Text files only stores texts 2 Binary Files are used to store binary data such as image, video, audio, text 3. There is a delimiter EOL (End of Line i.e n) 3. There is no delimiter

DIFFERENCE BETWEEN TEXT FILESAND BINARY FILES Text Files Binary Files 4. Due to delimiter text files takes more time to process. while reading or writing operations are performed on file. 4. No presence of delimiter makes files to process fast while reading or writing operations are performed on file. 5. Text files easy to understand because these files are in human readable form 5. Binary files are difficult to understand.

DIFFERENCE BETWEEN TEXT FILESAND BINARY FILES Text Files Binary Files 6. Text files are having extension .txt 6. Binary files are having .dat extension 7. Programming on text files are very easy. 7. Programming on binary files are difficult.

DIFFERENCE BETWEEN TEXT FILES AND BINARY FILES TEXT FILE BINARY FILE 1. Bits represent character. 1. Bits represent a custom data. 2. Less prone to get corrupt as changes reflect as soon as the file is opened and can easily be undone 2. Can easily get corrupted, even a single bit change may corrupt the file.

DIFFERENCE BETWEEN TEXT FILES AND BINARY FILES TEXT FILE BINARY FILE 3. Can store only plain text in a file. 3. Can store different types of data (image, audio, text) in a single file. 4. Widely used file format and can be opened using any simple text editor. 4. Developed especially for an application and may not be understood by other applications.

DIFFERENCE BETWEEN TEXT FILES AND BINARY FILES TEXT FILE BINARY FILE 5. Mostly .txt and .rtf are used as extensions to text files. 5. Can have any application defined extension.

PYTHON FILE OBJECT ATTRIBUTES File attributes give information about the file and file state. Attribute Function name Returns the name of the file closed Returns true if file is closed. False otherwise. mode The mode in which file is open. softspace Returns a Boolean that indicates whether a space character needs to be printed before another value when using the print statement.

OTHER METHODS OF FILEOBJECT Method Function readable() Returns True/False whether file is readable writable() Returns True/False whether file is writable fileno() Return the Integer descriptor used by Python to request I/O operations from Operating System flush() Clears the internal buffer for the file.

OTHER METHODS OF FILEOBJECT Method Function isatty() Returns True if file is connected to a Tele-TYpewriter (TTY) device or something similar. truncate([size) Truncate the file, up to specified bytes. next(iterator,[def ault]) Iterate over a file when file is used as an iterator, stops iteration when reaches end-of-file (EOF) for reading.

HANDLING FILES THROUGH OS MODULE

HANDLING FILES THROUGH OS MODULE The os module of Python allows you to perform Operating System dependent operations such as making a folder, listing contents of a folder, know about a process, end a process etc.. Let's see some useful os module methods that can help you to handle files and folders in your program.

ABSOLUTE PATH AND RELATIVE PATH

ABSOLUTE PATH Absolute path of file is file location, where in it starts from the top most directory ABSOLUTE PATH

RELATIVE PATH Relative Path of file is file location, where in it starts from the current working directory Myfoldermyfile.txt RELATIVE PATH

HANDLING FILES THROUGH OS MODULE Method Function os.makedirs() Create a new folder os.listdir() List the contents of a folder os.getcwd() Show current working directory os.path.getsize() show file size in bytes of file passed in parameter os.path.isfile() Is passed parameter a file os.path.isdir() Is passed parameter a folder os.chdir Change directory/folder

HANDLING FILES THROUGH OS MODULE Method Function os.rename(current,new) Rename a file os.remove(file_name) Delete a file

PROGRAMS 1. Write a function to create a text file containing following data Neither apple nor pine are in pineapple. Boxing rings are square. Writers write, but fingers don't fing. Overlook and oversee are opposites. A house can burn up as it burns down. An alarm goes off by going on.

PROGRAMS 2. Read back the entire file content using read() or readlines () and display on screen. 3. Append more text of your choice in the file and display the content of file with line numbers prefixed to line. 4. Display last line of file. Contd..

PROGRAMS 5. Display first line from 10th character onwards 6. Read and display a line from the file. Ask user to provide the line number to be read.

PROGRAMS 7. A text file named MATTER.TXT contains some text, which needs to be displayed such that every next character is separated by a symbol ‘#’. 8. Write a statement in Python to open a text file STORY.TXT so that new contents can be added at the end of it.

PROGRAMS 9. Write a method in Python to read lines from a text file INDIA.TXT, to find and display the occurrence of the word ‘‘India’’. For example : If the content of the file is ‘‘India is the fastest growing economy. India is looking for more investments around the globe. The whole world is looking at India as a great market. Most of the Indians can foresee the heights that India is capable of reaching.’’ The output should be 4.

PROGRAMS 10. Write a function to count total number of spaces, lines and characters in a given line of text

PROGRAMS 11. Write a function to count total number of digits in a given line of text

PROGRAMS 12. Write a function to copy the content of notes.txt to sub.txt NOTES.txt FILE

PROGRAMS 12. Write a function to copy the content of notes.txt to sub.txt

PROGRAM - OUTPUT 12. Write a function to copy the content of notes.txt to sub.txt SUB.txt FILE

PROGRAM - OUTPUT 13. Write a function to append or add a line of text in notes.txt NOTES.txt FILE

PROGRAMS 13. Write a function to append or add a line of text in notes.txt

PROGRAM -OUTPUT 13. Write a function to append or add a line of text in notes.txt

PROGRAMS 14. Write a function to display total number of lines in a notes.txt file. NOTES.txt FILE

PROGRAMS 14. Write a function to display total number of lines in a notes.txt file.

PROGRAM - OUTPUT 14. Write a function to display total number of lines in a notes.txt file. OUTPUT

PROGRAMS 14. Write a function in python to count the total number of lines in a file ‘Mem.txt’ ANTOHER METHOD

PROGRAMS 14. Write a function in python to count the total number of lines in a file ‘Mem.txt’ ‘Mem.txt’ file contains

PROGRAMS 14. Write a function in python to count the total number of lines in a file ‘Mem.txt’

PROGRAMS 15. Write a function to display last line of notes.txt file. NOTES.txt FILE

PROGRAMS 15. Write a function to display last line of notes.txt file.

PROGRAM - OUTPUT OUTPUT 15. Write a function to display last line of notes.txt file.

PROGRAMS 16. Write a function COUNT_DO( ) in Python to count the presence of a word ‘do’ in a text file “MEMO.TXT”. Example : If the content of the file “MEMO.TXT” is as follows: I will do it, if you request me to do it. It would have been done much earlier. The function COUNT_DO( ) will display the following message: Count of -do- in flie:

PROGRAMS 17. Write a function in Python to count the no. of “Me” or “My” words present in a text file “DIARY.TXT”. If the file “DIARY.TXT” content is as follows : My first book was Me and My family. It gave me chance to be known to the world. The output of the function should be Count of Me/ My in file :

PROGRAMS 18. Write a function in Python to count and display the number of lines starting with alphabet ‘A’ present in a text file “LINES.TXT”. Example: If the file “LINES.TXT” contains the following lines, A boy is playing there. There is a playground. An aeroplane is in the sky. Alphabets and numbers are allowed in the password. The function should display the output as 3.

PROGRAMS 19. Write a function in Python to read the content of a text file “DELHI.TXT” and display all those lines on screen, which are Either starting with ‘D’ or starting with ‘M’. DELHI.TXT File

PROGRAMS 20. Write a function in Python to count the number of alphabets present in a text file “NOTES.TXT”. NOTES.TXT FILE

CBSE QUESTION PAPER 2015 Delhi

CBSE QUESTION PAPER 2015 Delhi 4(a) Differentiate between the following : 1 (i) f = open(‘diary.txt’, ‘r’) (ii) f = open(‘diary.txt’, ‘w’) 4(b) Write a method in python to read the content from a text file diary.txt line by line and display the same on screen. 2

CBSE QUESTION PAPER 2016 Delhi 4. (a) Write a statement in Python to perform the following operations : 1  To open a text file “BOOK.TXT” in read mode  To open a text file “BOOK.TXT” in write mode 4(b) Write a method in python to read the content from a text file diary.txt line by line and display the same on screen. 2

CBSE QUESTION PAPER 2017 Delhi 4 (a) Differentiate between file modes r+ and rb+ with respect to Python. 1 4(b) Write a method in Python to read lines from a text file MYNOTES.TXT, and display those lines, which are starting with the alphabet K 2

CBSE QUESTION PAPER 2018 AI 4 (a) Write a statement in Python to open a text file STORY.TXT so that new contents can be added at the end of it. 1 4 (b) Write a method in Python to read lines from a text file INDIA.TXT, to find and display the occurrence of the word ‘‘India’’. 2 For example : If the content of the file is ‘‘India is the fastest growing economy.

CBSE QUESTION PAPER 2018 AI India is looking for more investments around the globe. The whole world is looking at India as a great market. Most of the Indians can foresee the heights that India is capable of reaching.’’ The output should be 4. 2

ADDITIONAL PROGRAMS 1. Write a Python program to read an entire text file. 2. Write a Python program to read first n lines of a file. 3. Write a Python program to append text to a file and display the text. 4. Write a Python program to read last n lines of a file. 5. Write a Python program to read last n lines of a file.

5. Write a Python program to read a file line by line and store it into a list. 6. Write a Python program to read a file line by line store it into a variable. 7. Write a Python program to read a file line by line store it into an array. 8. Write a python program to find the longest words. 9. Write a Python program to count the number of lines in a text file. 10. Write a Python program to count the frequency of words in a file. ADDITIONAL PROGRAMS

CLASS TEST 1. Write a program to count total no of spaces,words,characters,lines in a msg.txt file. 2.What is file? 3.Differentiate between text files and binary files. 4.Write a program to copy the content of notes.txt from 3rd character to till end of file to para.txt 5. Write a program to create binary file Class : XII Time: 40 Min Topic: FILE HANDLING Max Marks: 40 Each Question carries 4 Marks

Chapter 08 data file handling

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Chapter 08 data file handling