Due by 11:59pm on Wednesday, January 24.

Starter Files

Download lab01.zip. Inside the archive, you will find starter files for the questions in this lab, along with a copy of the Ok autograder.

Required Questions

Review

python3 ok -q FUNCTION

print("DEBUG:", x)

>>> 1 / 5
0.2

>>> 25 / 4
6.25

>>> 4 / 2
2.0

>>> 5 / 0
ZeroDivisionError

>>> 1 // 5 # truncate result of true division
0

>>> 25 // 4
6

>>> 4 // 2
2

>>> 5 // 0
ZeroDivisionError

>>> 1 % 5
1

>>> 25 % 4
1

>>> 4 % 2
0

>>> 5 % 0
ZeroDivisionError

x % y == 0

def what_prints():
    print('Hello World!')
    return 'Exiting this function.'
    print('61A is awesome!')

>>> what_prints()
Hello World!
'Exiting this function.'

What Would Python Display? (WWPD)

Q1: WWPD: Control

Use Ok to test your knowledge with the following "What Would Python Display?" questions:

python3 ok -q control -u
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>>> def xk(c, d):
...     if c == 4:
...         return 6
...     elif d >= 4:
...         return 6 + 7 + c
...     else:
...         return 25
>>> xk(10, 10)
______
23
>>> xk(10, 6)
______
23
>>> xk(4, 6)
______
6
>>> xk(0, 0)
______
25

>>> def how_big(x):
...     if x > 10:
...         print('huge')
...     elif x > 5:
...         return 'big'
...     if x > 0:
...         print('positive')
...     else:
...         print(0)
>>> how_big(7)         # A returned string is displayed with single quotes
______
'big'
>>> print(how_big(7))  # A printed string has no quotes
______
big
>>> how_big(12)
______
huge
positive
>>> print(how_big(12))
______
huge
positive
None
>>> print(how_big(1), how_big(0))
______
positive
0
None None

>>> n = 3
>>> while n >= 0:
...     n -= 1
...     print(n)
______
2
1
0
-1

>>> negative = -12
>>> while negative:  # All numbers are true values except 0
...    if negative + 6:
...        print(negative)
...    negative += 3
______
-12
-9
-3

Q2: Debugging Quiz

The following is a quick quiz on different debugging techniques that will be helpful for you to use in this class. You can refer to the debugging article to answer the questions.

Use Ok to test your understanding:

python3 ok -q debugging-quiz -u
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Write Code

Q3: Falling Factorial

Let's write a function falling, which is a "falling" factorial that takes two arguments, n and k, and returns the product of k consecutive numbers, starting from n and working downwards. When k is 0, the function should return 1.

def falling(n, k):
    """Compute the falling factorial of n to depth k.

    >>> falling(6, 3)  # 6 * 5 * 4
    120
    >>> falling(4, 3)  # 4 * 3 * 2
    24
    >>> falling(4, 1)  # 4
    4
    >>> falling(4, 0)
    1
    """
    "*** YOUR CODE HERE ***"

Use Ok to test your code:

python3 ok -q falling
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Q4: Divisible By k

Write a function divisible_by_k that takes positive integers n and k. It prints all positive integers less than or equal to n that are divisible by k from smallest to largest. Then, it returns how many numbers were printed.

def divisible_by_k(n, k):
    """
    >>> a = divisible_by_k(10, 2)  # 2, 4, 6, 8, and 10 are divisible by 2
    2
    4
    6
    8
    10
    >>> a
    5
    >>> b = divisible_by_k(3, 1)  # 1, 2, and 3 are divisible by 1
    1
    2
    3
    >>> b
    3
    >>> c = divisible_by_k(6, 7)  # There are no integers up to 6 divisible by 7
    >>> c
    0
    """
    "*** YOUR CODE HERE ***"

Use Ok to test your code:

python3 ok -q divisible_by_k
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Q5: Sum Digits

Write a function that takes in a nonnegative integer and sums its digits. (Using floor division and modulo might be helpful here!)

def sum_digits(y):
    """Sum all the digits of y.

    >>> sum_digits(10) # 1 + 0 = 1
    1
    >>> sum_digits(4224) # 4 + 2 + 2 + 4 = 12
    12
    >>> sum_digits(1234567890)
    45
    >>> a = sum_digits(123) # make sure that you are using return rather than print
    >>> a
    6
    """
    "*** YOUR CODE HERE ***"

Use Ok to test your code:

python3 ok -q sum_digits
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Syllabus Quiz

Q6: Syllabus Quiz

Please fill out the Syllabus Quiz, which confirms your understanding of CS 61A course policies.

Check Your Score Locally

You can locally check your score on each question of this assignment by running

python3 ok --score

This does NOT submit the assignment! When you are satisfied with your score, submit the assignment to Gradescope to receive credit for it.

Submit

Submit this assignment by uploading any files you've edited to the appropriate Gradescope assignment. Lab 00 has detailed instructions.

In addition, all students who are not in the mega lab must complete this attendance form. Submit this form each week, whether you attend lab or missed it for a good reason. The attendance form is not required for mega section students.

Optional Questions

These questions are optional. If you don't complete them, you will still receive credit for lab. They are great practice, so do them anyway!

Q7: WWPD: What If?

Use Ok to test your knowledge with the following "What Would Python Display?" questions:

python3 ok -q if-statements -u
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Hint: print (unlike return) does not cause the function to exit.

>>> def ab(c, d):
...     if c > 5:
...         print(c)
...     elif c > 7:
...         print(d)
...     print('foo')
>>> ab(10, 20)
______
10
foo

>>> def bake(cake, make):
...     if cake == 0:
...         cake = cake + 1
...         print(cake)
...     if cake == 1:
...         print(make)
...     else:
...         return cake
...     return make
>>> bake(0, 29)
______
1
29
29
>>> bake(1, "mashed potatoes")
______
mashed potatoes
'mashed potatoes'

Q8: Double Eights

Write a function that takes in a number and determines if the digits contain two adjacent 8s.

def double_eights(n):
    """Return true if n has two eights in a row.
    >>> double_eights(8)
    False
    >>> double_eights(88)
    True
    >>> double_eights(2882)
    True
    >>> double_eights(880088)
    True
    >>> double_eights(12345)
    False
    >>> double_eights(80808080)
    False
    """
    "*** YOUR CODE HERE ***"

Use Ok to test your code:

python3 ok -q double_eights
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