Python String Methods: The Complete Exam Reference

Strings are immutable

You cannot change a string in place. Every string method returns a new string.

s = "hello"
s.upper()        # returns "HELLO" — doesn't change s
print(s)         # "hello" — unchanged

# Correct:
s = s.upper()    # reassign
print(s)         # "HELLO"

Key string methods

Know these methods cold — they appear constantly.

s = "  Hello, World!  "

s.strip()           # "Hello, World!"
s.lower()           # "  hello, world!  "
s.upper()           # "  HELLO, WORLD!  "
s.replace("l","L")  # "  HeLLo, WorLd!  "
s.startswith("  H") # True
s.endswith("!  ")   # True
s.count("l")        # 3
s.find("World")     # 9 (index), or -1 if not found
s.index("World")    # 9, but raises ValueError if missing

"hello world".split()     # ["hello", "world"]
"a,b,c".split(",")        # ["a", "b", "c"]
", ".join(["a","b","c"])  # "a, b, c"

String formatting — f-strings

f-strings (Python 3.6+) are the modern way to format strings.

name = "Alice"
score = 92.5

print(f"Name: {name}, Score: {score:.1f}")
# "Name: Alice, Score: 92.5"

pi = 3.14159
print(f"{pi:.2f}")     # "3.14"
print(f"{1000:,}")     # "1,000"
print(f"{'hi':>10}")   # "        hi"

String slicing

Strings support the same slicing syntax as lists.

s = "Python"

print(s[0])      # "P"
print(s[-1])     # "n"
print(s[1:4])    # "yth"
print(s[::-1])   # "nohtyP"  — reversed
print(s[::2])    # "Pto"

Useful string checks

These methods return True or False.

"hello123".isalnum()    # True
"hello".isalpha()       # True
"123".isdigit()         # True
"  ".isspace()          # True
"Hello World".istitle() # True
"HELLO".isupper()       # True
"hello".islower()       # True

Exam tip

The most common string mistake in exams is forgetting strings are immutable. `s.upper()` doesn't modify s — you must write `s = s.upper()`. Watch for questions that call a method then print the original variable.