Week 3 — conditionals continued

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 A or B short-circuit?
• Procedure: Evaluate and/or left to right with short-circuit: and stops at first false; or stops at first true. Parentheses override default grouping.
• Variations / traps: Watch for: and/or confused with mathematical inequalities.

Formula chain (compressed)

nested if → decision table → and/or precedence → elif ladder order.

1. Nested if — if A: if B: ... — compound conditions
2. and/or precedence — and before or — use parentheses when unsure
3. elif chain — first true branch wins — mutually exclusive cases
4. Boolean ops — not, and, or — combine predicates
5. Decision table — rows = cases, cols = outcomes — trace before coding

Deep study

Programming in Python · Week 3 — Nested conditionals

Week map

Logical operator notation

• A and B → both must be true → x > 0 and x < 10 true only inside (0,10).
• A or B → at least one true → day == "Sat" or day == "Sun for weekend.
• not A → negation → not (x == 5) same as x != 5 for values.
• Short-circuit: False and f() does not call f(); True or g() skips g().

Truth tables (mini)

De Morgan’s laws

• not (A and B) ≡ not A or not B
• not (A or B) ≡ not A and not B

Nested if structure

python
Run Inline
x = 6
y = 2
if x > 5:
    if y > 5:
        print("both")
    else:
        print("outer only")
else:
    print("neither")

Pattern families

Easy — Compound predicate

• Evaluate and/or on two compares.
• Predict result of not on simple inequality.
• Short-circuit: second operand may not run.

Medium — Nested branch trace

• Two-level nesting with prints in each block.
• Identify which else runs.
• Convert word problem “if A and B then … else if C …” to code shape.

Hard — Decision table to code

• Mutually exclusive cases as if / elif chain.
• Negated compound conditions via de Morgan.
• Equivalent rewrites: nested if vs single compound predicate.

Worked mini-examples

python
Run Inline
temp = 22
humid = 80
if temp > 18 and humid < 70:
    comfort = "dry warm"
else:
    comfort = "other"
# comfort = "other" (humid fails)

python
Run Inline
d = "Sat"
if d == "Fri" or d == "Sat" or d == "Sun":
    kind = "off"
else:
    kind = "work"
# kind = "off"

python
Run Inline
age = 16
licensed = False
# not (age >= 18 and licensed)
if not (age >= 18 and licensed):
    can_drive = False
else:
    can_drive = True
# can_drive False

python
Run Inline
a, b = 3, 3
if a > 0:
    if b > 0:
        sign = "++"
    else:
        sign = "+-"
else:
    sign = "-"
# sign = "++"

Traps

• and confused with “between” — need two inequalities: low <= x and x <= high.
• Dangling else paired with wrong if after editing indentation.
• or is inclusive — both true still satisfies or.
• Negating without parentheses: not x > 5 parses as (not x) > 5 — wrong; use not (x > 5).
• Nested structure duplicated work — two separate if x>0 and if y>0 differ from if x>0 and y>0.

Diagnostic (try yourself)

1. What is result?

python
Run Inline
n = 7
if n % 2 == 0 and n > 5:
    result = "A"
elif n % 2 == 1 and n > 5:
    result = "B"
else:
    result = "C"

1. Rewrite without not ( ... and ... ) using de Morgan:

python
Run Inline
if not (x < 0 or x > 100):
    ok = True

1. What prints?

python
Run Inline
p, q = 2, 10
if p > 0:
    if q < 5:
        print(1)
    else:
        print(2)
else:
    print(3)

1. For integers a and b, write one if condition that is true exactly when both are positive.
2. if True or expensive(): — is expensive() called? Why?

ChatGPT prep archive

• Chatty reference archive

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

Core concepts

• and / or / not: and needs both true; or needs at least one; not flips.
• Nested if: inner test only when outer is true; scope of each block matters.
• Decision table: rows are cases; columns are conditions; one action column.
• De Morgan: not (A and B) equals not A or not B; not (A or B) equals not A and not B.

Notation & vocabulary

Pattern families

Easy — Compound predicate

Medium — Nested branch trace

Hard — Decision table to code

Drill these on the pattern atlas — filter to week 3.

Traps

• and/or confused with mathematical inequalities.
• Dangling else attaching to wrong if.
• not (x > 0 and x < 10) mishandled without de Morgan.
• Treating or as exclusive (Python or allows both true).

Retrieval prompts

1. When does A or B short-circuit?
2. Rewrite not (p and q) without not on and.
3. How does nesting change which else runs?

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 3.
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