[Type B] File Handling - Chapter 5 Sumita Arora

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3. Consider the file ‘`poemBTH.txt`‘ given above (in previous question). What output will be produced by following code fragment?

Python

obj1 = open("poemBTH.txt", "r")
s1 = obj1.readline()
s2.readline(10)
s3 = obj1.read(15)
print(s3)
print(obj1.readline())
obj1.close()

Answer: The code contains an error and produces the following output:

Traceback (most recent call last):
  File "<stdin>", line 3, in <module>
  File "<stdin>", line 2, in readline
NameError: name 's2' is not defined

Explanation:

Here’s a breakdown of the error message:

Line causing the error: s2.readline(10)
Error: NameError: name ‘s2’ is not defined
Traceback: This indicates the path of function calls leading to the error.
- File "<stdin>", line 3, in <module>: The error occurred on line 3 of the code you provided (which is typically executed from standard input, hence “<stdin>”).
- File "<stdin>", line 2, in readline: The error originated within the readline function call on line 2.
NameError: This signifies a name-related error, specifically that the name referenced doesn’t exist.
name ‘s2’ is not defined: The specific error message clarifies that the variable s2 is being used, but it hasn’t been defined or assigned a value in the current scope.

Running the code would result in this full error message, highlighting the absence of the variable s2.

But, here’s the expected output if the error is fixed:

nd boundless Love
I behold the border

Fixed Code Explanation:

File Handling: The code begins by correctly opening the file “poemBTH.txt” in read mode ('r') and assigning it to the file object obj1.
Initial Reads:
- s1 = obj1.readline() reads the first line of the poem (“God made the Earth;”) and stores it in the variable s1.
Error:
- s2.readline(10) attempts to read 10 characters from s2. However, s2 is undefined, leading to an error. This line should be changed to obj1.readline(10) to read the next 10 characters from the file.
Subsequent Reads (assuming the error is fixed):
- s3 = obj1.read(15) reads the following 15 characters (“nd boundless Love”) and stores them in s3.
- print(s3) prints the content of s3, displaying “nd boundless Love”.
- print(obj1.readline()) reads the remaining content of the current line (including a newline character) and prints “I behold the border”.
File closure: obj1.close() closes the file object, releasing resources.

Fixing the Error:

To fix the code, replace s2.readline(10) with:

Python

obj1.readline(10)  # Read the next 10 characters from the file object

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