Homework 1 Solutions

Solution Files

You can find the solutions in hw01.py.


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Required Questions

Q1: A Plus Abs B

Python's operator module contains two-argument functions such as add and sub for Python's built-in arithmetic operators. For example, add(2, 3) evalutes to 5, just like the expression 2 + 3.

Fill in the blanks in the following function for adding a to the absolute value of b, without calling abs. You may not modify any of the provided code other than the two blanks.

def a_plus_abs_b(a, b):
    """Return a+abs(b), but without calling abs.

    >>> a_plus_abs_b(2, 3)
    5
    >>> a_plus_abs_b(2, -3)
    5
    >>> a_plus_abs_b(-1, 4)
    3
    >>> a_plus_abs_b(-1, -4)
    3
    """
    if b < 0:

        f = sub
    else:

        f = add
    return f(a, b)

Use Ok to test your code:

python3 ok -q a_plus_abs_b

Use Ok to run the local syntax checker (which checks that you didn't modify any of the provided code other than the two blanks):

python3 ok -q a_plus_abs_b_syntax_check

If b is positive, we add the numbers together. If b is negative, we subtract the numbers. Therefore, we choose the operator add or sub based on the sign of b.

Q2: Two of Three

Write a function that takes three positive numbers as arguments and returns the sum of the squares of the two smallest numbers. Use only a single line for the body of the function.

def two_of_three(i, j, k):
    """Return m*m + n*n, where m and n are the two smallest members of the
    positive numbers i, j, and k.

    >>> two_of_three(1, 2, 3)
    5
    >>> two_of_three(5, 3, 1)
    10
    >>> two_of_three(10, 2, 8)
    68
    >>> two_of_three(5, 5, 5)
    50
    """

    return min(i*i+j*j, i*i+k*k, j*j+k*k)
    # Alternate solution
def two_of_three_alternate(i, j, k):
    return i**2 + j**2 + k**2 - max(i, j, k)**2

Hint: Consider using the max or min function:

>>> max(1, 2, 3)
3
>>> min(-1, -2, -3)
-3

Use Ok to test your code:

python3 ok -q two_of_three

Use Ok to run the local syntax checker (which checks that you used only a single line for the body of the function):

python3 ok -q two_of_three_syntax_check

We use the fact that if x>y and y>0, then square(x)>square(y). So, we can take the min of the sum of squares of all pairs. The min function can take an arbitrary number of arguments.

Alternatively, we can do the sum of squares of all the numbers. Then we pick the largest value, and subtract the square of that.

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 Assignment

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