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String Formatting (.format())

.format() inserts values into a string by replacing {} placeholders

Understanding String Formatting (.format()) in Python

What it does: {} placeholders are filled in order by the .format() arguments. :.2f formats a float to 2 decimal places. {} is a placeholder — .format() fills it in with the argument. {} marks where the value from .format() gets inserted. Each {} is replaced by the matching argument: 2, 3, 5. You can't + a string and number directly — .format() converts them for you. In an f-string, {name} is replaced by the variable's value. {name} is replaced by 'Bo'.

Common mistakes: Missing parentheses and argument: .format(name) needs (). Use curly braces {} for placeholders, not parentheses ().

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This module's key terms are also in a printable crossword (Modules 31–40) and word search (Modules 21–40).

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Learning

Duo

What does 'Hi {}'.format('Alice') return?

'Hi Alice''Hi {}'

Matches

❌ '{} and {}'.format('a')

↓

Error: Not enough arguments for {}

Applying

Meanings

Term

{}

Meaning

Placeholder in .format() that is replaced by the argument value.

Practice

name = 'Alice'

Testing

Gaps

print('Hello '.format(name))

Check Answer

Spots

2age = 12

3msg = 'Hello {}'.format

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Quick Questions

1. What does 'Hi {}'.format('Alice') return?

A. 'Hi {}'

B. 'Hi Alice' ✓

{} is a placeholder — .format() fills it in with the argument

2. What does {} represent in .format()?

A. Curly braces to print

B. A placeholder for a value ✓

{} marks where the value from .format() gets inserted

3. '{} + {} = {}'.format(2, 3, 5) returns?

A. '2 + 3 = 5' ✓

B. '{} + {} = {}'

Each {} is replaced by the matching argument: 2, 3, 5

4. What's the advantage of .format() over + concatenation?

A. Handles mixed types automatically ✓

B. It's faster

You can't + a string and number directly — .format() converts them for you

5. What does f'Hi {name}' do?

A. Inserts the variable name's value ✓

B. Prints 'Hi {name}'

In an f-string, {name} is replaced by the variable's value

Match the Pairs

'{} and {}'.format('a') → Error: Not enough arguments for {}

'{name}'.format('Alice') → Error: Named placeholder needs keyword arg

'{} is {}'.format('Bob', 15) → Valid: Bob is 15

'{:.2f}'.format(3.14159) → Ok: Returns '3.14'

print('{} + {} = {}'.format(1,2,3)) → Output: 1 + 2 = 3

print('{name}'.format(name='Ali')) → Output: Ali

Key Term

{}

Placeholder in .format() that is replaced by the argument value.~~.format()

Fill in the Blanks

1. name = 'Alice' print('Hello {}'.format(name))

2. age = 15 print('Age: {}'.format( age))

3. name = 'Bob' print(f'{name} is here')

4. price = 9.99 print('{:.2f}'.format(price))

5. a = 5 b = 3 print(f'{a} + {b} = {a + b}')

Spot the Error

Question 1

A name = 'Alice'

B age = 12

C msg = 'Hello {}'.format

D print(msg)

Line C — Missing parentheses and argument: .format(name) needs ()

Question 2

A name = 'Alice'

B age = 12

C msg = 'Hi (name), age (age)'.format(name='Alice', age=12)

D print(msg)

Line C — Use curly braces {} for placeholders, not parentheses ()

Question 3

A name = 'Alice'

B age = 12

C msg = f'Hi [name], age [age]'

D print(msg)

Line C — f-strings use {curly braces}, not [square brackets]

Question 4

A name = 'Alice'

B age = 12

C msg = 'Hello {}'.format()

D print(msg)

Line C — One {} placeholder but no argument provided

Question 5

A template = '(name) and (age)'

B name = 'Alice'

C msg = template.format(name='Alice', age=12)

D print(msg)

Line A — Use curly braces {} for placeholders, not parentheses ()

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