(a) Write a point of difference between append (a) and write (w) modes in a text file. Write a program in Pyth

Question

Q. (a) Write a point of difference between append

(a) and write (w) modes in a text file. Write a program in Python that defines and calls the following user defined functions :

(i) Add_Teacher() : It accepts the values from the user and inserts record of a teacher to a csv file 'Teacher.csv'. Each record consists of a list with field elements as T_id, Tname and desig to store teacher ID, teacher name and designation respectively.

(ii) Search_Teacher() : To display the records of all the PGT (designation) teachers.

(OR)

(b) Write one point of difference between seek() and tell() functions in file handling. Write a program in Python that defines and calls the following user defined functions :

(i) Add_Device() : The function accepts and adds records of the peripheral devices to a csv file 'peripheral.csv'. Each record consists of a list with field elements as P_id, P_name and Price to store peripheral device ID, device name, and price respectively.

(ii) Count_Device() : To count and display number of peripheral devices, whose price is less than Rs. 1000.

CBSECBSE Class XII Board 2023Subjective· 5mImportance★★★★★

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Part (a)Concept understanding — File Handling Methods

File Handling Methods: A First Look

Think about the last time you saved a document on your computer. You clicked "Save," gave it a name, and later opened it again to continue working. That simple act—storing information so you can retrieve it later—is the entire reason file handling exists. Every time you work with a file, whether it's a Word document, a PDF, or even a photo, you are performing file handling.

At its core, file handling is the process of creating, reading, updating, and deleting files through a computer program. It is how a program talks to the storage on your machine—the hard drive or SSD—rather than just working with data that disappears when you close the program.

The Two Fundamental Modes

When a program wants to work with a file, it must first open that file. Opening a file is like unlocking a drawer: you decide what you want to do with it before you start. There are two basic intentions:

Reading – You want to look at the contents of the file without changing anything. The file stays exactly as it is.
Writing – You want to put new content into the file, either by starting fresh (overwriting everything) or by adding to what is already there (appending).

These two intentions define the mode in which you open the file. A file opened for reading cannot be written to, and a file opened for writing cannot be read from—at least not in the simplest approach. This separation exists to prevent accidents: you do not want a program that is supposed to only display your data to accidentally erase it.

Note

In many programming languages, you can open a file in "read and write" mode, but that is a more advanced technique. For a beginner, think of reading and writing as two separate keys that open different locks on the same drawer.

The Lifecycle of a File Operation

Every file handling operation follows a fixed sequence. You cannot skip a step without causing trouble.

Open the file – You tell the program which file you want and what you intend to do with it (read or write). The program checks whether the file exists (for reading) or whether it can create a new one (for writing).
Perform the operation – You either read the data from the file into your program's memory, or you write data from your program into the file. This step can happen many times—you might read one line, then another, then another.
Close the file – You tell the program you are done. This step is crucial. Closing a file saves any changes you made and frees up the file so other programs can use it.

Important

Forgetting to close a file is like leaving a tap running. The file may remain locked, data might not be saved properly, and your program could waste memory. Always close what you open.

Why This Matters for a Commerce or Humanities Student

You might wonder why a student of commerce or humanities needs to understand file handling. The answer is simple: almost every modern business, government office, and research project deals with data stored in files.

A commerce student analyzing sales records will need to read data from a spreadsheet file, process it, and write the results to a new file.
A humanities student working with historical documents might need to read text files containing old letters, clean up the formatting, and save the cleaned version.
Anyone managing a database or a website will encounter file handling when uploading images, generating reports, or backing up information. …

Part (b)Concept understanding — File Handling Methods

File Handling Methods: A First Look

The Two Fundamental Modes

Reading – You want to look at the contents of the file without changing anything. The file stays exactly as it is.
Writing – You want to put new content into the file, either by starting fresh (overwriting everything) or by adding to what is already there (appending).

Note

The Lifecycle of a File Operation

Every file handling operation follows a fixed sequence. You cannot skip a step without causing trouble.

Open the file – You tell the program which file you want and what you intend to do with it (read or write). The program checks whether the file exists (for reading) or whether it can create a new one (for writing).
Perform the operation – You either read the data from the file into your program's memory, or you write data from your program into the file. This step can happen many times—you might read one line, then another, then another.
Close the file – You tell the program you are done. This step is crucial. Closing a file saves any changes you made and frees up the file so other programs can use it.

Important

Forgetting to close a file is like leaving a tap running. The file may remain locked, data might not be saved properly, and your program could waste memory. Always close what you open.

Why This Matters for a Commerce or Humanities Student

A commerce student analyzing sales records will need to read data from a spreadsheet file, process it, and write the results to a new file.
A humanities student working with historical documents might need to read text files containing old letters, clean up the formatting, and save the cleaned version.
Anyone managing a database or a website will encounter file handling when uploading images, generating reports, or backing up information. …

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Part (a)

Difference — append ('a') vs write ('w'): In 'w' mode, if the file already exists its contents are erased (truncated) before writing; in 'a' mode the existing contents are kept and new data is added at the end. (Both create the file if it does not exist.)

import csv

def Add_Teacher():
    with open('Teacher.csv', 'a', newline='') as f:
        w = csv.writer(f)
        rec = [input("T_id: "), input("Tname: "), input("desig: ")]
        w.writerow(rec)

def Search_Teacher():
    with open('Teacher.csv', 'r', newline='') as f:
        for row in csv.reader(f):
            if len(row) >= 3 and row[2].upper() == 'PGT':
                print(row)

Add_Teacher()
Search_Teacher()

For a stored PGT record ['T1', 'Asha', 'PGT'], Search_Teacher() prints:

['T1', 'Asha', 'PGT'] …

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Part (a): 'w' erases existing content, 'a' keeps it and adds at the end; Add_Teacher() appends a teacher record, Search_Teacher() lists all PGT teachers.

Part (b): tell() returns the pointer position, seek() moves it; Add_Device() appends a device record, Count_Device() counts devices priced under Rs. 1000.

Part (a)

append vs write. Both modes create the file if it is absent. The decisive difference is what they do to an existing file:

'w' (write): the file is truncated — all previous content is deleted — and writing starts from the beginning. Use it to create fresh / overwrite.
'a' (append): the previous content is preserved and the file pointer is placed at the end, so new data is added after the old data. Use it to keep adding records (e.g. logs, new rows).

Because we keep adding teacher records, Add_Teacher() opens the CSV in 'a' mode. Search_Teacher() reads the file and prints rows whose third field (designation) equals PGT.

import csv

def Add_Teacher():
    with open('Teacher.csv', 'a', newline='') as f:      # append: keeps old records
        w = csv.writer(f)
        t_id  = input("Enter Teacher ID: ")
        tname = input("Enter Teacher Name: ")
        desig = input("Enter Designation: ")
        w.writerow([t_id, tname, desig])

def Search_Teacher():
    with open('Teacher.csv', 'r', newline='') as f:
        for row in csv.reader(f):
            if len(row) >= 3 and row[2].upper() == 'PGT':
                print(row)

Add_Teacher()
Search_Teacher()

If the file already holds ['T1','Asha','PGT'] and ['T2','Ravi','TGT'], Search_Teacher() prints:

['T1', 'Asha', 'PGT'] …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2024Set 91/41 markMCQ
$Q. Consider the following Python statement: F=open('CONTENT.TXT') Which of the following is an invalid statement in Python? (A) F.seek(1,0) (B) F.seek(0,1) (C) F.seek(0,-1) (D) F.seek(0,2)$
›Reveal solutionSolution
The seek() method in Python's file handling allows you to change the current position of the file pointer, but its whence argument, which specifies the reference point, must be one of three specific integer values: 0 (beginning), 1 (current position), or 2 (end of file).

In Python, interacting with files is a fundamental aspect of many programs, allowing us to store and retrieve data persistently. The statement F = open('CONTENT.TXT') is the first step in this process. It opens a file named CONTENT.TXT in the default read mode ('r') and returns a file object, which we've assigned to the variable F. This file object acts as a gateway, providing methods to perform operations like reading, writing, and, importantly, navigating within the file.

One crucial method for navigating within a file is seek(). Imagine a cursor in a text editor; seek() allows you to move this cursor to a specific location within the file. This is incredibly useful when you need to re-read a part of a file, skip certain sections, or write data at a precise point.

The seek() method takes two arguments: seek(offset, whence).

The offset argument specifies the number of bytes to move. This can be a positive or negative integer, depending on the whence argument.

The whence argument determines the reference point from which the offset is calculated. This is where the strict rules apply, and understanding these values is key to using seek() correctly.

There are only three valid integer values for whence:

0 (or os.SEEK_SET): This means the offset is relative to the beginning of the file. When whence is 0, the offset must be a non-negative integer, as you cannot move before the start of the file.

1 (or os.SEEK_CUR): This means the offset is relative to the current file position. The offset can be positive (to move forward) or negative (to move backward) from the current position.

2 (or os.SEEK_END): This means the offset is relative to the end of the file. When whence is 2, the offset is typically a non-positive integer (0 or negative) to move backward from the end of the file. A positive offset from the end would move beyond the file's actual content.

Important

The whence argument in F.seek(offset, whence) can only take the integer values 0, 1, or 2. Any other integer value will result in an OSError or ValueError.

Now, let's examine the given statements based on these rules: …
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CBSE 2023Set 91/11 markMCQ
$Q. The syntax of seek() is: file_object.seek(offset[,reference_point]) What is the default value of reference_point?$
(a) 0
(b) 1
(c) 2
(d) 3
›Reveal solutionSolution

The seek() method changes the file object's current position. Its reference_point argument, which specifies the starting point for the offset, defaults to 0 — the beginning of the file. Correct option: (a).

When you work with files, the operating system tracks your current position within the file — the "file pointer". The seek() method lets you move this pointer manually. Its syntax is file_object.seek(offset[, reference_point]), where offset is the number of bytes to move and reference_point is the position the offset is measured from.

There are three standard reference points:

reference_point Measured from Note
0 Beginning of the file Default; offset must be zero or positive
1 Current file position Offset may be positive or negative
2 End of the file Offset is usually zero or negative

Because moving to an absolute position from the start of a file is by far the most common need, seek() makes 0 the default. So f.seek(7) is exactly the same as f.seek(7, 0) — both move the pointer 7 bytes from the beginning. …
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CBSE 2023Set 91/41 markMCQ
$Q. The correct syntax of tell() is :$
(a) tell.file_object()
(b) file_object.tell()
(c) tell.file_object(1)
(d) file_object.tell(1)
›Reveal solutionSolution
In Python file handling, the tell() method is called on a file object using dot notation, with no arguments — the correct syntax is file_object.tell().

When you work with files in Python, you are essentially moving a cursor through a stream of data. Every time you read or write, that cursor advances. The tell() method is the tool that tells you exactly where that cursor is at any moment — it returns the current position (as an integer representing bytes from the beginning of the file).

The syntax follows the standard object-oriented pattern in Python. A file object — created by open() — has methods attached to it. You access those methods by writing the object's name, a dot, and then the method name. So file_object.tell() is the correct form. No argument is needed inside the parentheses because tell() simply reports the current position; it does not change it.

Note

The position returned by tell() is measured in bytes, not characters. For text files, this distinction matters when the file uses multi-byte encodings like UTF-8 — but for most exam purposes, you can treat it as the cursor's offset from the start.

Now look at the options given:

(a) tell.file_object() — This is wrong because it treats tell as if it were the object and file_object as a method. In Python, the object comes first, then the dot, then the method.

(b) file_object.tell() — This is correct. The file object is the thing that knows its position, and tell() is the method that asks it. …
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CBSE 2023Set 91/41 markMCQ
$Q. Q. 17 and 18 are Assertion (A) and Reasoning (R) based questions. Mark the correct choice as$
(a) Both (A) and (R) are true and (R) is the correct explanation for (A).
(b) Both (A) and (R) are true and (R) is not the correct explanation for (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true. Assertion (A) : readlines() reads all the lines from a text file and returns the lines along with newline as a list of strings. Reasoning (R) : readline() can read the entire text file line by line without using any looping statements.
›Reveal solutionSolution
The readlines() method reads all lines into a list, while readline() reads one line at a time, requiring a loop to process an entire file.

When working with text files in Python, a common task is to read their contents. Python provides several methods for this, each suited for different scenarios. Understanding the nuances of these methods, particularly readlines() and readline(), is crucial for efficient and correct file handling. These methods allow us to access the data stored in a file, whether we need it all at once or line by line.

The readlines() method is designed for situations where you need to load the entire content of a text file into memory as a collection of individual lines. When you call readlines() on an open file object, it performs the following actions:

It reads every single line from the current position in the file until the end of the file is reached.

It collects these lines into a list.

Each element in this list is a string, representing one line from the file.

Crucially, each of these string elements retains the newline character (\n) at its end, which marks the termination of a line in the text file.

Note

The newline character (\n) is an invisible character that signifies the end of a line and causes the cursor to move to the beginning of the next line. When readlines() returns a list of strings, these \n characters are included in the strings, unless they are explicitly removed (e.g., using strip()).

In contrast, the readline() method operates differently. Its purpose is to read a file one line at a time, which is particularly useful when dealing with very large files that might not fit entirely into memory, or when you need to process each line individually before moving to the next.

When readline() is called, it reads only the next single line from the file.

It returns this line as a single string.

Similar to readlines(), this string also includes the newline character (\n) at its end, if present in the file.

If readline() is called again, it reads the subsequent line. This sequential reading continues until the end of the file. When the end of the file is reached, subsequent calls to readline() will return an empty string ('').

Important

To read the entire text file line by line using readline(), you must employ a looping construct, such as a while loop or a for loop (though a for loop directly over the file object is often more Pythonic for line-by-line iteration). Without a loop, readline() will only ever read the first line (or the next single line if called multiple times manually).

Now, let's evaluate the given Assertion and Reasoning: …
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reference_point	Measured from	Note
`0`	Beginning of the file	Default; offset must be zero or positive
`1`	Current file position	Offset may be positive or negative
`2`	End of the file	Offset is usually zero or negative

Q.(a) Write a point of difference between append

Part (a)

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