Question 1

Strings are immutable

Accepted Answer

Strings in Python are immutable - you cannot change a character in place using index assignment. Attempting s[0] = 'H' raises TypeError: 'str' object does not support item assignment. To 'modify' a string, build a new one: s = 'H' + s[1:] or use s.replace('h', 'H', 1).

Question 2

f-string interpolation

Accepted Answer

f-strings evaluate the expressions inside {} at runtime and insert the results. {name} inserts 'world', and {n * 2} evaluates 42 * 2 = 84 and inserts '84'. f-strings support any valid Python expression: function calls, arithmetic, attribute access, and more.

Question 3

split() and join() round-trip

Accepted Answer

split(',') breaks the string on commas into ['one', 'two', 'three']. join() takes an iterable of strings and concatenates them with the separator in between. ' | '.join(['one', 'two', 'three']) produces 'one | two | three'. The separator comes from the string, not the argument.

Question 4

f-string format specifiers

Accepted Answer

The format spec :.2f after the colon means: format as a fixed-point float with 2 decimal places. 3.14159 rounded to 2 decimal places is 3.14. Other common specs: :.0f (no decimals), :e (scientific notation), :,d (integer with thousands separator), :>10 (right-align in 10 chars).

Question 5

str.replace() returns a new string

Accepted Answer

Strings are immutable, so replace() returns a new string - it does not modify 's' in place. The result was not assigned back to anything, so s is still 'aabbcc'. The fix is: s = s.replace('b', 'x').

Question 6

Substring check with in

Accepted Answer

'in' on strings checks for substring membership and is case-sensitive. 'gram' appears inside 'programming', so it's True. 'python' (lowercase p) does not appear - the string starts with uppercase 'P', so it's False. For case-insensitive checks, use 'python' in s.lower().

Question 7

strip() removes leading and trailing whitespace

Accepted Answer

strip() removes leading and trailing whitespace (spaces, tabs, newlines). The original string is 15 characters. After stripping the 2 leading and 2 trailing spaces, 'hello world' is 11 characters. Use lstrip() to strip only the left side and rstrip() for only the right.

Question 8

Triple-quoted string newlines

Accepted Answer

Triple-quoted strings preserve literal newlines. 'line1' is 5 chars, the newline is 1 char, 'line2' is 5 chars - total 11. The triple quotes themselves are not part of the string. Triple-quoted strings are used for multi-line strings and docstrings; the content starts immediately after the opening quotes.

Question 9

Case methods return new strings

Accepted Answer

Like all string methods, upper() returns a new string and does not modify the original. The result is discarded because it wasn't assigned. s still refers to 'Hello World'. To keep the uppercase version: s = s.upper().

Question 10

split() default splits on whitespace

Accepted Answer

Calling split() with no arguments splits on any run of whitespace and discards empty strings from leading, trailing, and consecutive spaces. The result is clean: ['hello', 'world'] with length 2. This is different from split(' ') (one space), which would produce empty strings for each extra space character.

Question 11

strip() with a custom character set

Accepted Answer

When you pass a string argument to strip(), it removes any characters in that set from both ends - not just a substring. strip('*') removes all leading and trailing asterisks, leaving 'hello'. The argument is a set of characters to remove, not a prefix/suffix to match exactly.

Question 12

in checks for substring, not a character set

Accepted Answer

'ace' is a contiguous substring starting at index 1 of 'racecar', so 'ace' in s is True. 'ca' also appears at index 2 ('racecar'), making it True as well. The in operator checks for a contiguous sequence of characters, not just any combination of characters from the set.

Question 13

Triple-quoted string with leading newline

Accepted Answer

The triple-quoted string starts immediately after the opening """. The first character is a newline (1 char), followed by 'hello' (5 chars), for a total of 6. This is a common source of confusion: if you open the triple quote and immediately press Enter, that newline is part of the string. To avoid the leading newline in multi-line docstrings, put the first line of text right after the opening quotes.