Week 2 — conditionals

Quiz 2 scope: Weeks 1–8 per IITM May 2026 foundation courses. Source baseline: IITM BS admissions important-dates calendar · May 2026 cycle. Times on assessments are operational conventions — verify hall ticket.

Week map

Classify → Represent → Execute → Trap-check

• Recognize: Ask: When does elif run relative to if?
• Procedure: Evaluate only until first true predicate. Skip remaining elif/else. If none true, only else runs—or no branch if else missing.
• Variations / traps: Watch for: elif after a true if still evaluated (it is skipped).

Formula chain (compressed)

predicate → if/elif/else (first true wins) → and/or short-circuit.

1. Branch — if cond: ... elif: ... else: — at most one block runs
2. and — A and B — both must be true
3. or — A or B — at least one true
4. Equality — == vs = — compare vs assign
5. Truthiness — 0, "", [], None → falsy — if without explicit bool

Deep study

Programming in Python · Week 2 — Conditionals

Week map

Conditional notation

• if cond: → conditional block → runs body only when cond is True.
• elif cond: → else-if → tested only if all prior branches failed.
• else: → fallback → runs when every test above was false.
• cond → predicate → expression with boolean result → x >= 10, name == "Ada".

Comparison operators

Truthiness

• Falsy: 0, 0.0, False, None, "", [], {}, ().
• Truthy: most other values, including nonzero numbers and non-empty strings.

python
Run Inline
score = 0
if score:
    print("played")
else:
    print("skipped")

Branch selection rules

1. Evaluate if condition. If true, run its block and skip all elif and else.
2. Else evaluate first elif. If true, run it and skip rest.
3. If none true, run else if present; if no else, no block runs.

python
Run Inline
n = 14
if n < 10:
    label = "low"
elif n < 20:
    label = "mid"
else:
    label = "high"
# label is "mid"

Pattern families

Easy — Which branch runs?

• Single if / else with numeric compare.
• Predict print output from one predicate.
• Identify when else runs.

Medium — elif chains and boundaries

• Inclusive vs exclusive thresholds (<= vs <).
• Overlapping conditions — only first true branch executes.
• Assign variable in branches; trace final value.

Hard — Truthiness and edge inputs

• Empty string vs "0" string (truthy).
• if x: vs if x == True (usually prefer explicit compare for clarity).
• Multiple variables set in different branches — know which path ran.

Worked mini-examples

python
Run Inline
x = 25
if x > 30:
    print("A")
elif x > 20:
    print("B")
elif x > 10:
    print("C")
else:
    print("D")

python
Run Inline
k = 3
if k > 5:
    t = 1
# no else
# t may not exist — NameError if referenced

python
Run Inline
age = 18
if age >= 18:
    status = "adult"
else:
    status = "minor"
# status = "adult" (18 counts)

python
Run Inline
name = ""
if name:
    print("hi")
else:
    print("empty")
# prints empty

Traps

• elif still evaluated mentally when if was true — it is skipped entirely.
• Off-by-one on inclusive bounds.
• Assigning in one branch but using variable assuming another branch ran.
• == True with integers: only 1 equals True oddly; prefer if flag: or if flag is True rarely.
• Dangling logic: two separate if statements both may run — different from if / elif.

Diagnostic (try yourself)

1. What is printed?

python
Run Inline
v = 12
if v > 15:
    print("X")
elif v > 8:
    print("Y")
else:
    print("Z")

1. After this code, what is w?

python
Run Inline
w = 5
if w < 3:
    w = 10
elif w < 7:
    w = 20
else:
    w = 30

1. What is printed?

python
Run Inline
flag = 0
if flag:
    print("on")
else:
    print("off")

1. Rewrite using only if and else (no elif): assign "pass" when score >= 40, else "fail". Variable score already exists.
2. Two separate if statements both test x > 0. First prints "A", second prints "B". If x = 5, what prints? If x = -1, what prints?

ChatGPT prep archive

• Chatty reference archive

Archived import for extra depth — complements the notes above, not official IITM material.

Core concepts

• if / elif / else: exactly one branch runs when predicates are tested in order.
• Predicate: expression with bool result; comparisons and ==, !=, <, >, <=, >=.
• Truthiness: empty string, 0, empty list are falsy; most other values truthy.
• Indentation defines block body—must be consistent.

Notation & vocabulary

Pattern families

Easy — Which branch runs?

Medium — Boundary comparisons

Hard — Truthiness trap

Drill these on the pattern atlas — filter to week 2.

Traps

• elif after a true if still evaluated (it is skipped).
• Confusing is with == for value equality.
• Missing else when all paths must assign a variable.
• Off-by-one on inclusive <= vs exclusive <.

Retrieval prompts

1. When does elif run relative to if?
2. Which values are falsy in Python?
3. What prints if all if/elif tests fail and there is no else?

Practice loop

1. Read Deep study (if present) or core concepts once.
2. Recite the formula chain without looking.
3. Open one easy pattern on the interactive atlas for week 2.
4. Attempt without solutions; mark studied after an honest try.
5. Say one trap aloud before closing the tab.

Related

• Full weeks 1–8 prep guide
• Pattern atlas note
• Formula chain desk