← Python

File Operations – Write

.write() writes a string to a file opened in write or append mode

What it does: \n adds a newline so the next write starts on a new line. writelines() writes each string from the list — doesn't add newlines automatically. write() sends text to the file — print() sends it to the screen. Unlike print(), write() is literal — add '\n' to end each line. 'w' truncates the file to zero length before writing — use 'a' to preserve content. 'a' (append) keeps existing content and adds new text after it. write() returns the count of characters written — 'Hi' has 2 characters. Each write() call appends to the file — include '\n' to separate lines.

Common mistakes: write() only accepts strings: convert number with str(). Can't write in 'r' mode: use 'w' or 'a'.

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Learning

Duo

What does f.write('Hello') do?

Writes 'Hello' to the filePrints 'Hello'

Matches

❌ with open('f.txt','w') as f: f.write(42)

↓

Error: write() needs a string

Applying

Meanings

Term

.write(string)

Meaning

Writes a string to the file.

Practice

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

Testing

Gaps

f.('Hello')

Check Answer

Spots

2with open('f.txt', 'w') as f:

3 f.write(score)

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Quick Questions

1. What does f.write('Hello') do?

A. Writes 'Hello' to the file ✓

B. Prints 'Hello'

write() sends text to the file — print() sends it to the screen

2. Does write() add a newline automatically?

A. Yes always

B. No you must add \n yourself ✓

Unlike print(), write() is literal — add '\n' to end each line

3. What does 'w' mode do to existing content?

A. Erases it completely ✓

B. Keeps it

'w' truncates the file to zero length before writing — use 'a' to preserve content

4. How do you write without erasing?

A. Use 'w' mode

B. Use 'a' mode (append) ✓

'a' (append) keeps existing content and adds new text after it

5. f.write('Hi') returns?

A. 2 (number of characters written) ✓

B. 'Hi'

write() returns the count of characters written — 'Hi' has 2 characters

Match the Pairs

with open('f.txt','w') as f: f.write(42) → Error: write() needs a string

with open('f.txt','w') as f: pass f.write('hi') → Error: File already closed

with open('f.txt','w') as f: f.write('Hello\n') → Valid: Writes with newline

lines = ['a\n','b\n'] f.writelines(lines) → Ok: Write list of strings

with open('f.txt','w') as f: n = f.write('Hi') print(n) → Output: 2

with open('f.txt','w') as f: f.write('A') f.write('B') → Output: (file has 'AB')

Key Term

.write(string)

Writes a string to the file.~~.writelines(list)

Fill in the Blanks

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

2. with open('f.txt', 'a') as f: f.write('Append this')

3. f.write('Line 1\n')

4. score = 95 f.write('Score: ' + str(score))

5. lines = ['a\n', 'b\n'] f.writelines(lines)

Spot the Error

Question 1

A score = 42

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

C f.write(score)

D print('Saved!')

Line C — write() only accepts strings: convert number with str()

Question 2

A data = 'Hello World'

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

C f.write(data)

D print('Written!')

Line B — Can't write in 'r' mode: use 'w' or 'a'

Question 3

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

B f.write('Line 1')

C f.write('Line 2')

Line C — No newlines both lines will be on the same line: 'Line 1Line 2'

Question 4

A lines = ['a', 'b', 'c']

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

C f.writelines(lines)

D print('Written!')

Line C — writelines doesn't add \n: strings run together: 'abc'

Question 5

A f = open('f.txt', 'w')

B f.write('Hello')

C # no close

Line A — File never closed data may not be saved. Use 'with'.

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