Skip to content
๐ŸŽ“ Xin Yu's NoteZzz

W7: Comments and Docstrings, Variable Names and Global Constants, Namespaces, Timely Returns

Coming Up

  • Code Commenting and Documentation
  • Variable Names and Global Constants
  • Local VS Global Namespaces
  • Timely Returns

Code Commeting and Documentation

D1. Why is it important to write comments for the code we write? Wouldnโ€™t it save time, storage space and processing time to write code without comments?

D2. What is a docstring? What is its purpose?

E1. Fill in the blanks with comments and a docstring for the following function, which ๏ฌnds the most popular animals by counting ballots. An example for ballots is ['dog', 'pig', 'cat', 'pig', 'dog'], in which case the function returns ['dog', 'pig']. Thereโ€™s no de๏ฌnite right or wrong answer here, try to develop your own style.

Variable Names and Global Constants

D3. How should we choose variable names? How do good variable names add to the readability of code?

D4. What are magic numbers? How do we write code without them by using global constants?

E2. Consider the following programs. What are the problematic aspects of their variable names and use of magic numbers? What improvements would you make to improve readability?

a = float(input("Enter days: "))
b = a * 24
c = b * 60
d = c * 60
print("There are", b, "hours", c, "minutes,", d, "seconds in", a, "days")
word = input("Enter text: ")
x = 0
vowels = 0
word_2 = word.split()
for word_3 in word_2:
    x += 1
    for word_4 in word_3:
        if word_4.lower() in "aeiou":
            vowels += 1
if vowels/x > 0.4:
    print("Above threshold")

D5. What do we mean by mutability? Which data types are mutable out of what weโ€™ve seen?

Local VS Global Namespaces

D6. What is a namespace?

D7. What do we mean by local and global namespace? What is scope?

E4. What is the output of the following code? Classify the variables by which namespace they belong in.

def foo(x, y):
    a = 42
    x, y = y, x
    print(a, b, x, y)
a, b, x, y = 1, 2, 3, 4
foo(17, 4)
print(a, b, x, y)

E3. What is the output of this code? Why?

E4. Something is wrong with the following code. What will the current code output? How could you fix it?

def invert_grid(grid):
    new_grid = [[0] * len(grid[0])] * len(grid)
    # print(new_grid)

    for i in range(len(grid)):
        for j in range(len(grid[0])):
            new_grid[i][j] = 1 - grid[i][j]
            print(new_grid)
    return new_grid

grid = [[1, 0, 0], [0, 1, 0], [0, 0, 1]]
print(invert_grid(grid))

# [[0, 1, 1], [1, 0, 1], [1, 1, 0]]

D8. When is it useful to return early? How can it make our code safer and more ef๏ฌcient?

D9. What are helper functions? How can they make our code more readable and reusable?

E5. What is the output of the following code? Classify the variables by which namespace they belong in.

def foo(x, y):
    a = 42
    x, y = y, x
    print(a, b, x, y)

a, b, x, y = 1, 2, 3, 4
foo(17, 4)
print(a, b, x, y)

Timely Returns

E6. Compare the two functions below. Are they equivalent? Why would we prefer one over the other?

def noletter_1(words, letter='z'):
    for word in words:
        if letter in word:
            return False
    return True
def noletter_2(words, letter='z'):
    no_z = True
    for word in words:
        if letter in word:
            no_z = False
    return no_z

wordlist = ['zizzer'] + ['aardvark'] * 1_000_000
print(noletter_1(wordlist))
print(noletter_2(wordlist))

Problems

Problem 1

Write a function which takes a list of words and checks whether any of those words are palindromes (spelled the same way backwards as forwards, like โ€œhannahโ€). It should return True if there are any palindromes and False if there are none. Use a timely return to save some time! any_palindrome(['hannah', 'sven', 'mei']) should return True.

Problem 2

Write a function which takes a list of lists of integers and returns a sorted list containing the unique num- bers. For example unique_2d_list([[1, 5, 3], [2], [5, 1, 2]]) should return [1, 2, 3, 5].

Problem 3

Write a function which takes a string and returns a 2-tuple containing the most common character in the string and its frequency. In the case of a tie, it should return the character which occurs ๏ฌrst in the text. most_common_char('hi there') should return ('h', 2).