Reading files line by line in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the simplest way to open a file for reading in Python?

Use the open() function with the filename and mode 'r', like open('filename.txt', 'r').

beginner

How do you read a file line by line using a for loop in Python?

You can loop directly over the file object: <br>with open('file.txt', 'r') as f:<br>   for line in f:<br>     print(line)

beginner

Why is it good practice to use with when opening files?

Because with automatically closes the file when done, even if errors happen. This helps avoid resource leaks.

intermediate

What does the readline() method do?

It reads the next single line from the file each time it is called, returning it as a string including the newline character.

beginner

How can you remove the newline character from each line when reading a file?

Use the strip() method on the line string, like line.strip(), to remove whitespace including newlines.

Which Python statement correctly reads a file line by line?

A open('file.txt').read()

B with open('file.txt') as f: for line in f: print(line)

C file.read('file.txt')

D for line in open('file.txt').readlines(): print(line)

Option B uses a with statement and loops directly over the file object, which is the recommended way to read lines one by one.

What does the 'r' mode mean in open('file.txt', 'r')?

A Append mode, adds to the end

B Write mode, opens file for writing

C Read mode, opens file for reading

D Read and write mode

'r' stands for read mode, which opens the file only for reading.

What happens if you forget to close a file after reading?

A The file stays open, which can cause resource leaks

B Nothing, Python closes it automatically always

C The file deletes itself

D The file content is lost

If you don't close a file, it remains open and can cause resource leaks or lock the file.

Which method reads one line at a time from a file?

A read()

B open()

C readlines()

D readline()

The readline() method reads the next single line from the file.

How can you remove extra spaces and newline characters from a line read from a file?

A line.strip()

B line.remove()

C line.clear()

D line.delete()

The strip() method removes whitespace including newlines from the start and end of a string.

Explain how to read a file line by line in Python using a for loop.

Think about how you open the file and how you get each line one at a time.

Describe why using the with statement is important when working with files.

Consider what happens if your program crashes while the file is open.