File system interaction basics in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open a file named 'data.txt' in read mode.

Python

file = open('data.txt', '[1]')

Drag options to blanks, or click blank then click option'

Ax

Bw

Ca

Dr

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'w' which overwrites the file.

Using 'a' which appends instead of reading.

The mode 'r' opens the file for reading. Other modes are for writing or appending.

2fill in blank

medium

Complete the code to write the string 'Hello' to a file named 'output.txt'.

Python

with open('output.txt', '[1]') as f:
    f.write('Hello')

Drag options to blanks, or click blank then click option'

Aw

Br

Ca

Drb

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'r' which is read-only.

Using 'rb' which is read binary mode.

The mode 'w' opens the file for writing and creates it if it doesn't exist.

3fill in blank

hard

Fix the error in the code to read all lines from 'log.txt' into a list.

Python

with open('log.txt', 'r') as file:
    lines = file.[1]()

Drag options to blanks, or click blank then click option'

Areadlines

Bread

Creadline

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'readline' which reads only one line.

Using 'write' which is for writing, not reading.

The method readlines() reads all lines into a list. readline() reads only one line.

4fill in blank

hard

Fill both blanks to create a dictionary with filenames as keys and their sizes in bytes as values.

Python

import os
files = ['a.txt', 'b.txt', 'c.txt']
sizes = { [1] : os.path.[2](f) for f in files }

Drag options to blanks, or click blank then click option'

Af

Bgetsize

Cfiles

Dexists

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'files' as key which is the whole list.

Using 'exists' which checks if file exists, not size.

Use f as the key for each filename, and os.path.getsize(f) to get the file size.

5fill in blank

hard

Fill all three blanks to filter files larger than 1000 bytes and create a dictionary with uppercase filenames as keys and sizes as values.

Python

import os
files = ['x.log', 'y.log', 'z.log']
large_files = { [1] : [2] for f in files if os.path.getsize(f) [3] 1000 }

Drag options to blanks, or click blank then click option'

Af.upper()

Bos.path.getsize(f)

C>

Df.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in filter.

Using 'f.lower()' instead of uppercase.

Using wrong function for size.

Use f.upper() for uppercase keys, os.path.getsize(f) for values, and filter with > 1000 bytes.

Practice

1. What does the mode 'r' mean when opening a file with open() in Python?

easy

A. Open the file for reading only

B. Open the file for writing only

C. Open the file for appending data

D. Create a new file or overwrite existing

Solution

1. Step 1: Understand file modes in Python

   The mode 'r' stands for reading the file only, meaning you can read data but not change it.

2. Step 2: Compare with other modes

   Modes like 'w' are for writing (which overwrites), and 'a' is for appending. 'r' does not allow writing.

3. Final Answer:

   Open the file for reading only -> Option A

4. Quick Check:

   Mode 'r' = read only [OK]

Hint: Remember 'r' means read, 'w' means write, 'a' means append [OK]

Common Mistakes:

• Confusing 'r' with 'w' or 'a'
• Thinking 'r' creates a new file
• Trying to write to a file opened with 'r'

2. Which of the following is the correct syntax to open a file named 'data.txt' for writing in Python?

easy

A. open('data.txt', 'r')

B. open('data.txt', 'w')

C. open('data.txt', 'rw')

D. open('data.txt', 'a+')

Solution

1. Step 1: Identify the mode for writing

   The mode 'w' opens a file for writing and creates it if it doesn't exist or overwrites if it does.

2. Step 2: Check syntax correctness

   open('data.txt', 'w') is the correct syntax. 'r' is for reading, 'rw' is invalid, 'a+' is for appending and reading.

3. Final Answer:

   open('data.txt', 'w') -> Option B

4. Quick Check:

   Write mode = 'w' [OK]

Hint: Use 'w' to write or overwrite files [OK]

Common Mistakes:

• Using 'r' when intending to write
• Using invalid mode 'rw'
• Confusing 'a+' with 'w'

3. What will be the output of this code?

with open('test.txt', 'w') as f:
    f.write('Hello')

with open('test.txt', 'a') as f:
    f.write(' World')

with open('test.txt', 'r') as f:
    print(f.read())

medium

A. Error: file not found

B. Hello

C. Hello World

D. World

Solution

1. Step 1: Write 'Hello' to the file

   The first block opens 'test.txt' in write mode, which creates or clears the file, then writes 'Hello'.

2. Step 2: Append ' World' to the file

   The second block opens the file in append mode and adds ' World' after 'Hello'.

3. Step 3: Read and print the file content

   The last block reads the full content, which is 'Hello World', and prints it.

4. Final Answer:

   Hello World -> Option C

5. Quick Check:

   Write + append = 'Hello World' [OK]

Hint: Write clears file, append adds to end [OK]

Common Mistakes:

• Expecting append to overwrite
• Not closing files before reading
• Confusing write and append modes

4. What is wrong with this code snippet?

f = open('log.txt', 'r')
print(f.read())
f.write('New entry')
f.close()

medium

A. File is opened in read mode but write is attempted

B. File is not closed properly

C. Missing mode argument in open()

D. File path is incorrect

Solution

1. Step 1: Check file mode and operations

   The file is opened with mode 'r' which allows reading only.

2. Step 2: Identify invalid operation

   Calling f.write() on a file opened in read mode causes an error because writing is not allowed.

3. Final Answer:

   File is opened in read mode but write is attempted -> Option A

4. Quick Check:

   Write not allowed in 'r' mode [OK]

Hint: Don't write to files opened with 'r' mode [OK]

Common Mistakes:

• Trying to write without 'w' or 'a' mode
• Forgetting to close files
• Assuming 'r' mode allows writing

5. You want to read a file line by line and print only lines that contain the word 'error'. Which is the best way to do this in Python?

hard

A. open('log.txt', 'r').read().split('error')

B. f = open('log.txt', 'r')
lines = f.readlines()
for line in lines:
if line == 'error':
print(line)
f.close()

C. with open('log.txt', 'w') as f:
for line in f:
if 'error' in line:
print(line)

D. with open('log.txt', 'r') as f:
for line in f:
if 'error' in line:
print(line.strip())

Solution

1. Step 1: Use 'with' and read line by line

   with open('log.txt', 'r') as f: for line in f: if 'error' in line: print(line.strip()) uses 'with' to open the file safely and iterates line by line, which is memory efficient.

2. Step 2: Check condition and print matching lines

   It checks if 'error' is in each line and prints the line without extra spaces using strip().

3. Final Answer:

   with open('log.txt', 'r') as f: for line in f: if 'error' in line: print(line.strip()) -> Option D

4. Quick Check:

   Use 'with' + for line in file + condition [OK]

Hint: Use 'with' and loop lines to filter content [OK]

Common Mistakes:

• Opening file in 'w' mode when reading
• Comparing whole line to 'error' instead of substring
• Not closing file properly
• Using split incorrectly for line filtering