← Python

File Operations – Read

.read() reads the entire file content as a string; .readlines() reads lines into a list

What it does: readlines() returns a list where each element is one line of the file. Iterating over the file object reads one line at a time. .strip() removes the \n. read() loads everything at once — fine for small files, memory-hungry for large ones. readline() advances the cursor one line — call it again to get the next. Processing line by line keeps only one line in memory at a time. The file cursor stays where reading stopped — seek(0) resets it to the start. split('\n') breaks the big string wherever there's a newline character. readlines() preserves the \n — use line.strip() or line.rstrip() to remove it.

Common mistakes: Missing parentheses read is a method, call it with (). Missing parentheses readlines is a method.

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Learning

Duo

f.read() returns?

The entire file as one stringOne line

Matches

❌ with open('f.txt','w') as f: f.read()

↓

Error: Can't read in write mode

Applying

Meanings

Term

.read()

Meaning

Reads the entire file as one string.

Practice

with open('hello.txt', 'r') as f:

Testing

Gaps

content = f.()

Check Answer

Spots

1with open('f.txt') as f:

2 content = f.read

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Quick Questions

1. f.read() returns?

A. The entire file as one string ✓

B. One line

read() loads everything at once — fine for small files, memory-hungry for large ones

2. f.readlines() returns?

A. One string

B. A list of all lines ✓

readlines() gives you a list — each element is one line including its \n

3. f.readline() returns?

A. The next single line ✓

B. All lines

readline() advances the cursor one line — call it again to get the next

4. Why use line.strip()?

A. To split the line

B. To remove the \n newline character ✓

Each line from a file ends with \n — strip() removes that trailing whitespace

5. for line in f: what does this do?

A. Loops through each line ✓

B. Reads the whole file

Iterating the file object yields one line per loop — memory-efficient

Match the Pairs

with open('f.txt','w') as f: f.read() → Error: Can't read in write mode

with open('f.txt') as f: f.read() f.read() → Error: Second read returns empty

with open('f.txt') as f: lines = f.readlines() → Valid: Lines as a list

with open('f.txt') as f: for line in f: print(line.strip()) → Ok: Loop line by line

# file has 'Hello\nWorld' f.readline() → Output: 'Hello\n'

# file has 'Hi' print(f.read()) → Output: Hi

Key Term

.read()

Reads the entire file as one string.~~.readline()

Fill in the Blanks

1. with open('f.txt') as f: content = f.read() print(content)

2. with open('f.txt') as f: lines = f.readlines()

3. with open('f.txt') as f: first = f.readline()

4. for line in f: print(line.strip())

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

Spot the Error

Question 1

A with open('f.txt') as f:

B content = f.read

C print(content)

Line B — Missing parentheses read is a method, call it with ()

Question 2

A with open('f.txt') as f:

B lines = f.readlines

C print(lines)

Line B — Missing parentheses readlines is a method

Question 3

A with open('f.txt') as f:

B for line in f.readlines():

C print(line)

Line B — This works but is less efficient. Loop over f directly and use strip().

Question 4

A with open('f.txt') as f:

B content = f.read()

C content = f.read()

D print(content)

Line C — Second read() returns '' cursor is at end. Read once or use f.seek(0).

Question 5

A f = open('f.txt')

B for line in f:

C print(line)

D # forgot to close

Line A — File never closed. Use 'with' to auto-close.

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