Chapter 5: Integrated Problem-solving in Python - Lists and Strings D2 chap 2

Why Python?

• Python is easy to learn, resourceful, well-supported, and free.
• Some firms require workers to learn programming languages like Python.

Lists in Python

• Lists are ordered sequences that can store items of different data types.
• For array-like algorithms, data within lists should be of the same data type.

Basic Operations of Python Lists

• Creation:
  • list1 = ["David", "Lily", "Ben"]
  • list2 = [34, 23, 90, 56, 100]
• Initialization (assigning default values):
  • list3 = [0]*10
  • list4 = [""]*5
• Updating Elements:
  • list2[0] = 28
  • list2[1] = list2[2] - 5
• Output:
  • print(list1[1]) # Output: Lily
  • Looping through a list:
    python list2 = [34, 23, 90, 56, 100] for i in range(0, 5): print(list2[i])
• Copying a list:

  list2 = [34, 23, 90, 56, 100]
  new_list = [0]*5
  for i in range(0, 5):
      new_list[i] = list2[i]

List Operations

• Calculating the total:

  time = [15.1, 14.9, 15.6, 16.1, 16.8, 17.0, 16.9, 16.5]
  total = 0
  for i in range(0, 8):
      total = total + time[i]
  print(total)  # Output: 128.9

• Calculating the average:

  time = [15.1, 14.9, 15.6, 16.1, 16.8, 17.0, 16.9, 16.5]
  total = 0
  for i in range(0, 8):
      total = total + time[i]
  avg = total/8
  print(avg)  # Output: 16.1125

• $len()$ function: Returns the number of items in a list.

Searching for Items in a List

• Linear Search:

  target = int(input())
  found = False
  N = len(the_list)
  for i in range(0, N):
      if target == the_list[i]:
          found = True
  print(found)

• Using a while loop to find the first index:

  target = int(input())
  found = False
  index = -1
  i = 0
  N = len(the_list)
  while i < N and found == False:
      if target == the_list[i]:
          found = True
          index = i
      i = i + 1
  print(index)

• Counting items greater than a value:

  bound = int(input())
  count = 0
  N = len(the_list)
  for k in range(0, N):
      if the_list[k] > bound:
          count = count + 1
  print(count)

• Finding the largest value:

  largest = the_list[0]
  N = len(the_list)
  for i in range(1, N):
      if the_list[i] > largest:
          largest = the_list[i]
  print(largest)

• Checking if a list is sorted in ascending order:

  sorted_list = True
  N = len(the_list)
  for k in range(0, N-1):
      if the_list[k] > the_list[k+1]:
          sorted_list = False
  print(sorted_list)

List Manipulation

• Deleting an item at index $P$. Number of elements is reduced by one.

  N = len(the_list)
  for k in range(P, N-1):
      the_list[k] = the_list[k+1]
  N = N - 1

• Adding a new item new_data at index $P$.

  the_list = the_list + [0]
  N = len(the_list)
  for k in range(N-1, P, -1):
      the_list[k] = the_list[k-1]
  the_list[P] = new_data

• Moving the item at index $P$ to the first position:

  temp = the_list[P]
  for k in range(P, 0, -1):
      the_list[k] = the_list[k-1]
  the_list[0] = temp

Integrated Application of Python Strings

• Strings in Python can be modified. Values cannot be directly assigned to items in a string.
• Finding Length: Use the $len()$ function.
• Finding a Character:
  • Using a for loop:
    python the_string = "Work Hard!" target = "a" found = False N = len(the_string) for i in range (0, N): if target == the_string[i]: found = True print(found)
  • Using a while loop.
• Extracting Characters: Create substrings by extracting parts of strings.

Determining the Type of a Character

• Use ASCII values for comparisons.
• Features of ASCII:
  • Capital and small letters are in alphabetical order.
  • Numbers are in ascending order.