Python String Methods Class 11: find, count, replace, strip, split, join and isalpha Tests

Understand String Methods: find, count, replace, strip, split, join and the is-Tests (CBSE 11)

s = "banana"
print(s.count("an"), s.find("an"), s.find("an", 2))   # 2 1 3
print(s.replace("an", "AN"))                         # bANANa

String Methods: find, count, replace, strip, split, join and the is-Tests (CBSE 11): key facts

Case methods

• •upper() all capital
• •lower() all small
• •title() each word
• •capitalize() first letter only

They return new strings.

Search methods

• •find(x) index or -1
• •index(x) index or ValueError
• •count(x) non-overlapping
• •startswith and endswith give True or False

find is safe for a missing value.

Test methods

• •isalpha
• •isdigit
• •isalnum
• •islower
• •isupper
• •isspace

Spaces and symbols make the first three False.

Edit methods

• •strip lstrip rstrip remove edge spaces
• •replace(old, new)
• •split() makes a list
• •sep.join(list) makes a string

Original string never changes.

How to answer String Methods: find, count, replace, strip, split, join and the is-Tests (CBSE 11) questions

1. 1Write the string with indices if a position or count is needed.
2. 2Apply the first method and write the new string, number, list or Boolean it returns.
3. 3Apply the next method to that result, not to the original string.
4. 4For find, count and replace check overlapping and case; "A" and "a" are different.
5. 5Write lists with square brackets and quotes, and Booleans as True or False.

String Methods: find, count, replace, strip, split, join and the is-Tests (CBSE 11) in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Tricks to remember String Methods: find, count, replace, strip, split, join and the is-Tests (CBSE 11)

Short memory aids. Say each one aloud once, then use it on a question the same day.

• find is polite, index is strict

  find says -1 when the text is absent; index shouts ValueError.

  Use it when: Choosing between them in programs.

• Split and join are opposites

  split cuts a string into a list; join glues a list into a string.

  Use it when: Sentence and word programs.

• Methods do not edit

  Every method leaves s as it was; store the result if you want to keep it.

  Use it when: Output questions with an unused result.

String Methods: find, count, replace, strip, split, join and the is-Tests (CBSE 11): solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

s = "  Data Science  "
print(len(s), s.strip(), len(s.strip()))

s = "banana"
print(s.count("an"), s.find("an"), s.find("an", 2))
print(s.replace("an", "AN"))
print(s.replace("a", ""))
print(s)

line = "red,green,,blue"
parts = line.split(",")
print(parts, len(parts))
print("-".join(parts))
print("red green  blue".split())
print("key=value=x".partition("="))

s = "Hello World 2025!"
v = u = d = 0
for ch in s:
    if ch.lower() in "aeiou":
        v += 1
    if ch.isupper():
        u += 1
    if ch.isdigit():
        d += 1
print(v, u, d)

Where students lose marks in String Methods: find, count, replace, strip, split, join and the is-Tests (CBSE 11)

The slips examiners see most often, and what to write instead.

• ✗Mistake: Ignoring that a method returns a new string

  Writing the method call without storing or printing it.

  Wrong working

  s = "mango"; s.upper(); print(s) # mango

  Right working

  s = s.upper(); print(s) # MANGO

  ✓Do this: Assign or print the result.

  Usually costs: 1 mark

• ✗Mistake: Using index() where find() is meant

  Not noting the missing-value behaviour.

  Wrong working

  "abc".index("z") # ValueError

  Right working

  "abc".find("z") # -1

  ✓Do this: Use find when the text may be absent.

  Usually costs: 1 mark

• ✗Mistake: Thinking isalpha() accepts spaces

  Treating a phrase as letters.

  Wrong working

  "hello world".isalpha() is True

  Right working

  It is False because of the space

  ✓Do this: Any non-letter makes isalpha False.

  Usually costs: 1 mark

Practice questions on String Methods: find, count, replace, strip, split, join and the is-Tests (CBSE 11)

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   Which method makes the first letter of every word capital?
   (a) capitalize()
   (b) title()
   (c) upper()
   (d) swap()

   Hint

   Every word.

   Answer

   (b) title()

2. Q2 · 1 mark · Assertion-reasonHarder board level

   Assertion (A): For s = "mango", the statement s.upper() alone does not change s.
   Reason (R): Strings are immutable, so string methods return new strings.
   (a) Both A and R are true, and R is the correct explanation of A.
   (b) Both A and R are true, but R is not the correct explanation of A.
   (c) A is true, but R is false.
   (d) A is false, but R is true.

   Hint

   Return value.

   Answer

   (a) Both A and R are true, and R is the correct explanation of A.

3. Q3 · 4 marks · Short answerHarder board level

   Give the output:

   s = "hello world"
   print(s.title(), s.capitalize(), s.isalpha(), s.replace("l", "L", 2))

   (4 marks)

   Hint

   replace with a count changes only the first n matches.

   Answer

   title() gives Hello World; capitalize() gives Hello world; isalpha() is False because of the space; replace("l", "L", 2) changes the first two l letters (indices 2 and 3): heLLo world. Output: Hello World Hello world False heLLo world

4. Q4 · 3 marks · Short answerHarder board level

   Give the output:

   print("A123".isalnum(), "A 123".isalnum(), "123".isdigit(), "12.5".isdigit(), "abc".islower(), "   ".isspace())

   (3 marks)

   Hint

   Spaces and full stops are not letters or digits.

   Answer

   "A123" has letters and digits only: True; "A 123" has a space: False; "123" is all digits: True; "12.5" has a full stop: False; "abc" is all small: True; " " is only whitespace: True. Output: True False True False True True

5. Q5 · 5 marks · Short answerHOTS / competency

   Given e = "student@school.edu", write code to print the part before @, the part after @ and whether e ends with ".edu". Give the output, and say what goes wrong if the text has no @. (5 marks)

   Hint

   find returns -1 when absent.

   Answer

   i = e.find("@"); print(e[:i], e[i+1:], e.endswith(".edu")). The @ is at index 7, so e[:7] = student and e[8:] = school.edu. Output: student school.edu True. With no @, find returns -1, and e[:-1] would drop the last character, so first check that i != -1.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.What does find() return for a missing value?Show answer

   -1.

2. 2.What does split() return?Show answer

   A list of strings.

3. 3.What must a list contain to be used with join()?Show answer

   Strings only.

4. 4.What does strip() remove?Show answer

   Spaces at both ends of the string.

5. 5.Does replace() change the original string?Show answer

   No; it returns a new string.

String Methods: find, count, replace, strip, split, join and the is-Tests (CBSE 11): frequently asked questions