Review: Debugging Questions

Module 4: IDEs & Tools

Debugging Questions

Exercise

The following code is intended to remove duplicates from a list while preserving the original order of elements. However, it raises the error AttributeError: 'dict' object has no attribute 'add'. Identify and fix the error(s).

def remove_duplicates(seq: list) -> list:
  seen = {}
  result = []
  for item in seq:
    if item in seen:
      continue
    else:
      seen.add(item)  # Error
    result.append(item)
    return result

original_list = [5, 4, 3, 4, 5, 2, 1]
new_list = remove_duplicates(original_list)
print("New List:", new_list)  # Expected: [5, 4, 3, 2, 1]

Solution

Fix:

def remove_duplicates(seq: list) -> list:
  seen = set()
  result = []
  for item in seq:
    if item in seen:
      continue
    else:
      seen.add(item)  # Error
    result.append(item)
  return result

original_list = [5, 4, 3, 4, 5, 2, 1]
new_list = remove_duplicates(original_list)
print("New List:", new_list)  # Expected: [5, 4, 3, 2, 1]

Exercise

This code attempts to swap the values of two variables stored in a tuple without using a temporary variable. However, it results in an error TypeError: 'tuple' object does not support item assignment. Identify and fix the issue(s).

def swap_values(tup: tuple) -> tuple:
  tup[0], tup[1] = tup[1], tup[0]  # Error

my_tuple = (10, 20)
swapped_tuple = swap_values(my_tuple)
print("Swapped Tuple:", swapped_tuple)  # Expected: (20, 10)

Solution

Fix:

def swap_values(tup: tuple) -> tuple:
  ls = list(tup)
  ls[0], ls[1] = ls[1], ls[0]  # Error
  return tuple(ls)

my_tuple = (10, 20)
swapped_tuple = swap_values(my_tuple)
print("Swapped Tuple:", swapped_tuple)  # Expected: (20, 10)

Exercise

This code tries to modify a list while iterating over it to remove all occurrences of a specific value. However, it raises an error IndexError: list index out of range. Identify and fix the error(s).

def remove_value(lst: list, val: int) -> list:
  for i in range(len(lst)):
    if lst[i] == val:  # Error
      lst.pop(i)
  return lst

numbers = [1, 2, 3, 2, 4, 2, 5]
updated_numbers = remove_value(numbers, 2)
print("Updated Numbers:", updated_numbers)  # Expected: [1, 3, 4, 5]

Solution

Fix:

def remove_value(lst: list, val: int) -> list:
  result = []
  for i in range(len(lst)):
    if lst[i] != val:
      result.append(lst[i])
  return result

numbers = [1, 2, 3, 2, 4, 2, 5]
updated_numbers = remove_value(numbers, 2)
print("Updated Numbers:", updated_numbers)  # Expected: [1, 3, 4, 5]

Exercise

This code tries to modify a list while iterating over it to remove all occurrences of a specific value. However, it doesn’t remove all instances as intended. Identify and fix the error(s).

def remove_value(lst: list, val: int) -> list:
  for item in lst:
    if item == val:
      lst.remove(item)
  return lst

numbers = [1, 2, 3, 2, 4, 2, 2, 5]
updated_numbers = remove_value(numbers, 2)
print("Updated Numbers:", updated_numbers)
# Expected: [1, 3, 4, 5]
# Output: [1, 3, 4, 2, 5]

::: {.callout-tip collapse=“true”} ## Solution Fix:

:::
# NEVER modify the iterable you are looping through!

Exercise

This code is supposed to flatten a list of lists into a single list. However, it raises an error TypeError: 'int' object is not iterable. Find and fix the error(s).

def flatten(lst: list[list]) -> list:
  flat_list = []
  for sublist in lst:
    flat_list.extend(sublist)  # Error
  return flat_list

nested_list = [1, [2, 3], [4, [5, 6]], 7]
flattened = flatten(nested_list)
print("Flattened List:", flattened)
# Expected: [1, 2, 3, 4, 5, 6, 7]

Exercise

The code aims to count the frequency of each character in a string using a dictionary. However, it raises an exception when run KeyError: 'h'. Find and correct the error(s).

def char_frequency(s: str) -> int:
  freq = dict()
  for char in s:
    if char.isalpha():
      freq[char] += 1  # Error
  return freq

text = "hello world"
frequency = char_frequency(text)
print("Character Frequency:", frequency)
# Expected: {'h': 1, 'e': 1, 'l': 3, 'o': 2, 'w': 1, 'r': 1, 'd': 1}

Exercise

The following code is meant to merge two dictionaries, summing the values of common keys. However, it doesn’t produce the expected result. Identify and fix the error(s).

def merge_dicts(d1: dict, d2: dict) -> dict:
  merged = d1.copy()
  for key in d2.keys():
    if not (key in d1.keys()):
      continue
    merged[key] = d1.get(key, 0) + d2[key]
  return merged

dict_a = {'apple': 10, 'banana': 5}
dict_b = {'banana': 15, 'cherry': 20}
merged_dict = merge_dicts(dict_a, dict_b)
print("Merged Dictionary:", merged_dict)
# Expected: {'apple': 10, 'banana': 20, 'cherry': 20}
# Output: {'apple': 10, 'banana': 20}

Exercise

This code attempts to create a set of tuples from a list of lists, intending to remove duplicate lists. However, it raises an error TypeError: unhashable type: 'list'. Identify and fix the issue(s).

list_of_lists = [[1, 2], [3, 4], [1, 2]]
unique_sets = set(list_of_lists)  # Error
print("Unique Sets:", unique_sets)  # Expected: {(1, 2), (3, 4)}

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