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String Methods (upper, lower, replace…)

String methods are called with dot notation on a string and return a new modified string

What it does: .strip() removes leading and trailing whitespace from the string. .split(',') splits the string at each comma into a list. upper() converts every character to uppercase. replace() swaps every occurrence of the first arg with the second. Strings are immutable — methods return a new modified string. 'hello' starts with 'he' — that's True. h-e-l-l-o contains two 'l' characters. 'll' starts at index 2: h(0) e(1) l(2)l(3).

Common mistakes: upper() returns a new string: must assign it back or print directly. Method names are lowercase: upper(), not Upper().

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Learning

Duo

What does 'hello'.upper() return?

'HELLO''Hello'

Matches

❌ name = 'hello' name.Upper()

↓

Error: Method names are lowercase

Applying

Meanings

Term

.upper()

Meaning

Returns the string in all uppercase letters.

Practice

name = 'hello'

Testing

Gaps

print(name.())

Check Answer

Spots

1name = 'hello'

2name.upper()

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Quick Questions

1. What does 'hello'.upper() return?

A. 'HELLO' ✓

B. 'Hello'

upper() converts every character to uppercase

2. What does 'HELLO'.lower() return?

A. 'Hello'

B. 'hello' ✓

lower() converts every character to lowercase

3. What does 'abc'.replace('b', 'x') return?

A. 'axc' ✓

B. 'abc'

replace() swaps every occurrence of the first arg with the second

4. Do string methods change the original string?

A. Yes

B. No they return a new string ✓

Strings are immutable — methods return a new modified string

5. What does ' hi '.strip() return?

A. 'hi' ✓

B. ' hi '

strip() removes whitespace (spaces, tabs, newlines) from both ends

Match the Pairs

name = 'hello' name.Upper() → Error: Method names are lowercase

'hello'.replace('l') → Error: replace() needs 2 arguments

' hi '.strip() → Valid: Returns 'hi'

'a,b,c'.split(',') → Ok: Returns ['a','b','c']

print('hello'.upper()) → Output: HELLO

print('hi'.replace('h','H')) → Output: Hi

Key Term

.upper()

Returns the string in all uppercase letters.~~.lower()

Fill in the Blanks

1. name = 'hello' print(name.upper())

2. name = 'HELLO' print(name.lower())

3. msg = 'I like cats' print(msg.replace('cats', 'dogs'))

4. text = ' hi ' print(text.strip())

5. csv = 'a,b,c' print(csv.split(','))

Spot the Error

Question 1

A name = 'hello'

B name.upper()

C print(name)

D print('Done')

Line B — upper() returns a new string: must assign it back or print directly

Question 2

A name = 'hello'

B result = name.Upper()

C print('Result:', result)

D print('Done')

Line B — Method names are lowercase: upper(), not Upper()

Question 3

A name = 'hello'

B result = upper(name)

C print('Result:', result)

D print('Done')

Line B — upper() is a string method: use name.upper(), not upper(name)

Question 4

A msg = 'hello'

B result = msg.replace('l')

C print('Result:', result)

D print('Done')

Line B — replace() needs two arguments: old and new

Question 5

A data = ' hi '

B cleaned = data.strip

C print('Cleaned:', cleaned)

D print('Done')

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

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