Session 4: the Wooclap questions

Warm-up 1

Calls inside calls are read from the inside out. Two ways to round a fee to cents. What does the program print?

fee = -2.675
print(round(abs(fee), 2), round(abs(fee) * 100) / 100)

1. 2.68 2.68
2. 2.67 2.68
3. 2.67 2.67
4. -2.67 -2.68

Warm-up 2

A function returns two values. What does the program print?

def low_high(prices):
    return min(prices), max(prices)

result = low_high([190.5, 187.2, 193.8])
low, high = low_high([190.5, 187.2, 193.8])
print(type(result).__name__, high)

1. TypeError on line 4
2. list 193.8
3. tuple 193.8
4. tuple 187.2

Warm-up 3

The same function, called with keywords. What does the program print?

def value(shares, price):
    return shares * price

print(value(price=190.5, shares=10), value(190.5, 10))

1. 1905.0 1905.0
2. TypeError on line 4
3. 1905.0 TypeError
4. 1905.0 19.05

Warm-up 4

A method belongs to a type. What happens?

tickers = "aapl,nesn".split(",")
print(tickers.upper())

1. AAPL,NESN
2. ['AAPL', 'NESN']
3. TypeError on line 2
4. AttributeError on line 2

Warm-up 5

Two random numbers from the same seed. What does the program print?

import random
random.seed(1)
a = random.random()
random.seed(1)
b = random.random()
print(a == b)

1. It changes every run
2. NameError on line 3
3. True
4. False

Warm-up 6

Two names for one object. What does the program print?

class Position:
    def __init__(self, ticker, shares):
        self.ticker = ticker
        self.shares = shares

a = Position("AAPL", 10)
b = a
b.shares = 12
print(a.shares)

1. 12
2. None
3. AttributeError on line 9
4. 10

Task 1 · print is not return

Two functions that look almost the same. Predict EVERYTHING the program shows, line by line, in order. Then say what a and b hold.

def value_p(shares, price):
    print(shares * price)

def value_r(shares, price):
    return shares * price

a = value_p(4, 102.3)
b = value_r(4, 102.3)
print(a, b)

What does the last line print?

1. Task 1: 409.2 None
2. Task 1: None None
3. Task 1: 409.2 409.2
4. Task 1: None 409.2

Task 2 · two variables called total

Predict the print. Then explain: the function assigns to total. Why is the total outside still 100.0?

total = 100.0

def add_fee(amount):
    total = amount + 2.5
    return total

x = add_fee(40.0)
print(x, total)

What does the print show?

1. 42.5 42.5
2. 102.5 100.0
3. 42.5 100.0
4. NameError

Task 3 · what the function changed

Two functions, each changes its parameter. Predict both prints. Why does the list outside change, and the number outside not?

def add_position(shares, n):
    shares.append(n)
    return len(shares)

def add_one(n):
    n = n + 1
    return n

shares = [10, 4, 2]
k = add_position(shares, 7)
print(k, shares)

m = 5
y = add_one(m)
print(m, y)

What does Task 3a print?

1. None [10, 4, 2, 7]
2. 3 [10, 4, 2]
3. 4 [10, 4, 2, 7]
4. 4 [10, 4, 2]

Task 4 · which methods change the value?

One string method chain, one list method. Predict all four printed values. Which method changed its object, and which returned a new one?

ticker = " nesn "
t2 = ticker.strip().upper()
shares = [10, 4, 2]
s2 = shares.sort()
print(repr(ticker), t2, shares, s2)

What does the print show?

1. 'NESN' NESN [2, 4, 10] [2, 4, 10]
2. 'NESN' NESN [2, 4, 10] None
3. ' nesn ' NESN [2, 4, 10] None
4. ' nesn ' NESN [10, 4, 2] [2, 4, 10]

Task 5 · the weight that lies

AAPL is worth 1905.0 of a 3338.2 CHF ledger. The function below computes its weight in percent. The call runs and prints a number. Is it right? Find the mistake and fix it so that no one can make it again.

def weight(value, total):
    return value / total * 100

print(f"{weight(3338.2, 1905.0):.1f}%")

What does the buggy call print?

1. TypeError
2. 1.8%
3. 57.1%
4. 175.2%

Check 1

What does this print?

def double(x):
    x * 2
print(double(3))

1. 6
2. None
3. 3
4. x * 2

Check 2

What does this print?

def diff(a, b=2):
    return a - b
print(diff(5), diff(b=1, a=5))

1. 5 4
2. 3 4
3. TypeError
4. 3 -4

Check 3

What does this print?

total = 10
def reset():
    total = 1
    return total
reset()
print(total)

1. NameError
2. 1
3. None
4. 10

Check 4

What does this print?

x = [3, 1, 2].sort(); print(x)

1. [1, 2, 3]
2. [3, 1, 2]
3. AttributeError
4. None

Check 5

What does this print?

print(" nesn ".strip().upper().replace("N", "M"))

1. MESM
2. MESN
3. MESM
4. NESN

Check 6

What does this print?

import math; print(math.ceil(2.1), math.floor(-2.1))

1. 2 -2
2. 2 -3
3. 3 -3
4. 3 -2

Check 7

What does this print?

def add_one(xs):
    xs.append(1)
a = []
add_one(a)
add_one(a)
print(a)

1. [1]
2. [1, 1]
3. []
4. None

Check 8

What does this print?

class Position:
    def __init__(self, ticker, shares, price):
        self.ticker = ticker
        self.shares = shares
        self.price = price
    def value(self):
        return self.shares * self.price

p = Position("NESN", 2, 5.0)
p.shares += 1
print(p.value())

1. 3
2. AttributeError
3. 15.0
4. 10.0

Check 9

What does this print?

import random; random.seed(1); a = random.randint(1, 6); random.seed(1); b = random.randint(1, 6); print(a == b)

1. None
2. True
3. It depends on the run
4. False

Check 10

In numpy, arr.shape and arr.sum() differ because…

1. There is no difference; the parentheses are optional
2. shape is an attribute (a stored fact); sum() is a method (an operation you call)
3. shape is a function from the math module
4. sum() is an attribute; shape is a method