Python Working with Files Exercises

In real-world Python programming, one of the most common tasks is working with files — reading from or writing to them. Whether you're processing logs, reading CSV data, storing user-generated content, or building automation tools, file handling is an essential skill.

Python provides a built-in function `open()` to access files on disk. It supports different modes like `'r'` for reading, `'w'` for writing, and `'a'` for appending. Once the file is opened, you can use methods like `.read()`, `.readline()`, or `.readlines()` to access its content. It's also a good practice to close the file after use, either manually or using a `with` block.

Consider the following code:

f = open("notes.txt", "r")
content = f.read()
f.close()
print(content)

What does this code do?

Opens notes.txt in read mode, reads all its content into a variable, closes the file, and prints the content.

Creates a new file called notes.txt and writes "r" into it.

Appends "notes.txt" to the variable f, but does not read its content.

Opens the file, prints its memory address, and then deletes the file automatically.

This code uses the open() function to open a file named "notes.txt" in read mode ("r"). The .read() method reads the entire content of the file as a single string, which is stored in the content variable.

After reading, the file is closed using f.close(), which is necessary to release system resources. Finally, print(content) displays the file’s contents on the screen.

Proper file handling ensures that resources are managed correctly, especially when working with large files or running scripts that read/write frequently. In modern Python code, it’s recommended to use:

with open("notes.txt", "r") as f:
    content = f.read()

This automatically handles closing the file even if an error occurs.

Which mode should be used to write data to a file, overwriting existing content?

"a"

"r"

"w"

"x"

The mode "w" stands for "write". When you open a file in this mode, it will overwrite the existing content of the file if it already exists. If the file does not exist, it creates a new one. Use this mode with caution to avoid data loss.

What is the purpose of using a `with` statement when working with files in Python?

To manually close the file after reading or writing

To ensure the file is automatically closed

To improve the performance of the program

To avoid using the read() function

The with statement in Python is used for resource management. When used with files, it ensures that the file is automatically closed once the block is exited, even if an exception occurs. This eliminates the need to explicitly call file.close() and prevents potential file leaks or errors.

Which of the following will open a file for both reading and writing?

open("file.txt", "r+")

open("file.txt", "r")

open("file.txt", "w")

open("file.txt", "a")

The mode "r+" opens a file for both reading and writing. Unlike "w" or "a", it does not truncate the file, and it requires that the file already exists. This mode is useful when you want to read and then modify content within a file.

What will the following code output if `info.txt` contains "Hello\nWorld"?

with open("info.txt", "r") as f:
    lines = f.readlines()
print(len(lines))

1

2

0

Error

The method readlines() reads all lines in the file and returns them as a list of strings. Since the file contains two lines separated by \n, the list will contain two elements: "Hello\n" and "World". Thus, len(lines) will return 2.

What does the following code snippet do?

with open("log.txt", "a") as f:
    f.write("New entry\n")

Reads the entire contents of log.txt.

Overwrites log.txt with "New entry".

Appends "New entry" to the end of log.txt.

Deletes the contents of log.txt.

Opening a file in append mode ("a") allows you to add new content to the end of the file without modifying the existing content. This snippet writes "New entry" followed by a newline character at the end of log.txt. If the file doesn’t exist, it will be created.

How can you read a file line by line efficiently without loading the entire file into memory?

f.read()

f.readlines()

f.read().splitlines()

for line in f:

Using a for loop directly on the file object (for line in f) is the most memory-efficient way to read a file line by line. It reads one line at a time during iteration, making it suitable for processing large files without consuming too much memory.

What will the following code print?

with open("data.txt", "w") as f:
    f.write("Line 1\nLine 2")

with open("data.txt", "r") as f:
    print(f.readlines())

['Line 1', 'Line 2']

['Line 1\\n', 'Line 2']

['Line 1\nLine 2']

['Line 1\n', 'Line 2']

The readlines() method returns a list of lines where each line ends with a newline character if present in the file. Since "Line 1\nLine 2" has a newline character only after "Line 1", the result is ['Line 1\n', 'Line 2']. This demonstrates how readlines() separates content based on line breaks.

What will happen if you try to open a non-existent file using mode `"r"`?

A new file is created.

The file opens successfully as an empty file.

An empty string is returned.

A FileNotFoundError is raised.

Opening a file in read mode ("r") requires the file to already exist. If it doesn't, Python raises a FileNotFoundError. To create a new file if it doesn't exist, you should use modes like "w", "a", or "x" instead.

Which method is best for writing a list of strings to a file?

lines = ["First\n", "Second\n", "Third\n"]

f.write(lines)

f.writeline(lines)

f.writelines(lines)

f.write(lines.join())

The writelines() method writes each string in the list to the file consecutively. It does not add newlines automatically, so you must ensure each string in the list includes \n if you want line breaks. It's more efficient than calling write() in a loop for each line.

What will be the output of the following code?

with open("sample.txt", "w") as f:
    f.write("1\\n2\\n3\\n")

with open("sample.txt", "r") as f:
    print(sum(int(line.strip()) for line in f))

6

123

0

Error

The code writes the numbers 1, 2, and 3 to the file sample.txt, each on a new line. Then it reads the file line by line, strips each line of whitespace, converts it to an integer, and sums them. This results in 1 + 2 + 3 = 6.

What will the following code output if `report.txt` contains the line "apple banana cherry"?

with open("report.txt", "r") as f:
    print(f.read().split()[1])

apple

banana

cherry

Error

The read() method reads the entire file content as a single string. The split() method splits the string by whitespace into a list of words: ['apple', 'banana', 'cherry']. Accessing index 1 returns the second word, 'banana'.

What does the `seek(0)` method do when working with files?

Skips the first line of the file

Deletes all file content before index 0

Resets the file cursor to the beginning

Rewinds the last write operation

The seek(0) method moves the file cursor back to the beginning of the file. This is especially useful when you need to reread a file after already reading it once, or when switching from writing to reading in modes like "r+".

How can you write binary data to a file in Python?

open("file.bin", "b")

open("file.bin", "wb")

open("file.bin", "r")

open("file.bin", "xb")

To write binary data to a file, you must open the file in binary write mode using "wb". This allows writing byte-like objects (such as those returned by bytes() or encoding strings). Mode "xb" is also binary, but it raises an error if the file already exists.

Which code will copy the contents of `source.txt` to `dest.txt`?

with open("source.txt", "r") as s, open("dest.txt", "w") as d:
    d.write(s.read())

with open("source.txt", "w") as s, open("dest.txt", "r") as d:
    d.write(s.read())

with open("source.txt", "a") as s, open("dest.txt", "a") as d:
    d.append(s.read())

with open("source.txt", "r") as s:
    print(s.read(), file=open("dest.txt", "w"))

To copy file content, you need to read from the source and write to the destination. Option 1 opens source.txt in read mode and dest.txt in write mode. Then it reads the entire content of the source file and writes it to the destination file. This is the simplest and correct way to copy plain text data from one file to another.

Given the following code, what will be the content of `notes.txt` after execution?

with open("notes.txt", "w") as f:
    f.write("Original line\\n")

with open("notes.txt", "r+") as f:
    f.write("Edited")

Original line
Edited

Editedinal line

Original line

The "r+" mode allows both reading and writing without truncating the file. When you write using f.write("Edited"), it overwrites characters from the current position (start of the file). So "Original line" becomes "Editedinal line" because only the first 6 characters are overwritten.

If a file is opened using `open("log.txt", "x")`, what happens if the file already exists?

The file will be overwritten.

The existing file will be opened for writing.

A new file is created regardless of existence.

FileExistsError will be raised.

The "x" mode is used to create a new file. If the file already exists, a FileExistsError is raised to avoid accidentally overwriting existing data. This is a safe way to ensure that you do not overwrite files unintentionally.

Consider this code. What does it print?

with open("data.txt", "w") as f:
    f.writelines(["a", "b", "c"])\n

with open("data.txt") as f:
    print(f.read())

a
b
c

abc

a b c

[a, b, c]

The writelines() method writes each item in the list directly to the file without adding any line breaks or spaces between them. Since the strings "a", "b", and "c" don’t include newline characters, they are written as "abc" in a single line.

Which file mode allows both reading and writing but does not truncate the file?

"w+"

"r+"

"a+"

"x+"

"r+" opens the file for both reading and writing, but unlike "w+", it does not truncate the file. This mode is ideal when you want to preserve existing content and modify or read it simultaneously. However, the file must already exist, or a FileNotFoundError will occur.

Which of the following will correctly write the string `'π = 3.14'` to a UTF-8 encoded file?

open("math.txt", "w").write("π = 3.14")

open("math.txt", "w", encoding="utf-8").write("π = 3.14")

open("math.txt", "wb").write("π = 3.14")

open("math.txt", "r", encoding="utf-8").write("π = 3.14")

To write Unicode characters like π safely, you must specify encoding="utf-8" when opening the file. This ensures that characters outside the ASCII range are handled correctly. Option 1 may work depending on system defaults but isn't reliable across all environments.

Python Working with Files Exercises

In real-world Python programming, one of the most common tasks is working with files — reading from or writing to them. Whether you're processing logs, reading CSV data, storing user-generated content, or building automation tools, file handling is an essential skill.

Consider the following code:

What does this code do?

Which mode should be used to write data to a file, overwriting existing content?

What is the purpose of using a with statement when working with files in Python?

Which of the following will open a file for both reading and writing?

What will the following code output if info.txt contains "Hello\nWorld"?

What does the following code snippet do?

How can you read a file line by line efficiently without loading the entire file into memory?

What will the following code print?

What will happen if you try to open a non-existent file using mode "r"?

Which method is best for writing a list of strings to a file?

What will be the output of the following code?

What will the following code output if report.txt contains the line "apple banana cherry"?

What does the seek(0) method do when working with files?

How can you write binary data to a file in Python?

Which code will copy the contents of source.txt to dest.txt?

Given the following code, what will be the content of notes.txt after execution?

If a file is opened using open("log.txt", "x"), what happens if the file already exists?

Consider this code. What does it print?

Which file mode allows both reading and writing but does not truncate the file?

Which of the following will correctly write the string 'π = 3.14' to a UTF-8 encoded file?

About This Exercise: Python – Working with Files

What is the purpose of using a `with` statement when working with files in Python?

What will the following code output if `info.txt` contains "Hello\nWorld"?

What will happen if you try to open a non-existent file using mode `"r"`?

What will the following code output if `report.txt` contains the line "apple banana cherry"?

What does the `seek(0)` method do when working with files?

Which code will copy the contents of `source.txt` to `dest.txt`?

Given the following code, what will be the content of `notes.txt` after execution?

If a file is opened using `open("log.txt", "x")`, what happens if the file already exists?

Which of the following will correctly write the string `'π = 3.14'` to a UTF-8 encoded file?