If Statements and Boolean Logic - Exam 1

What does == mean?

Compare values for equality; it does not assign.

What syntax begins a conditional block?

if condition: then an indented block.

When does elif execute?

Only if earlier branches were false and its condition is true.

When does else execute?

When no previous if/elif condition was true.

What is True and False?

False: both must be True for AND.

What is True or False?

True: at least one must be True for OR.

What is wrong with if x > 0: when x is a multi-element NumPy array?

The truth value is ambiguous; use a mask or .any()/.all().

Why can np.sin(np.pi) == 0 be False?

Floating-point rounding makes the result extremely close to zero, not exactly zero.

How do you check whether an array has ANY positive element?

(x > 0).any()

How do you check whether ALL array elements are positive?

(x > 0).all()

What does x < 3 check?

Whether x is strictly smaller than 3.

When do two if statements both run?

If each of their separate conditions is True.

How is if/elif different from two independent ifs?

An if/elif chain executes only the first matching branch.

For x=0, what does if x>0: print('P'); else: print('N') output?

N

For x=2, if x<0/elif x<5/else, which branch runs?

The elif branch because x is not negative but is less than 5.

What does not True evaluate to?

False

What does not (3>2) evaluate to?

False

What is False or False?

False

What is True and True?

True

Write a condition for x between 1 and 5 inclusive (scalar)

1 <= x <= 5

Write a scalar condition for x outside [1,5]

x < 1 or x > 5

Write code to print 'positive' only when x>0

if x > 0:

print('positive')

Write if/else setting y to abs(x), without np.abs

if x >= 0:

y = x

else:

y = -x

Why does an elif branch not run after an earlier if is True?

The chain stops at its first satisfied condition.

Where must the colon appear in if x>0: ?

At the end of the if header, before the indented body.

What does break do when an if condition inside a loop is met?

Immediately exits the loop; execution continues after the loop.

How do you test whether any entry of x exceeds 10?

(x > 10).any()

How do you test whether all entries of x are nonnegative?

(x >= 0).all()

What is the safer numeric test for f(x) near zero?

abs(fx) < tol, for a chosen small tolerance.