Python program to determine the position of characters in a string using index

In this post we discuss how to write a Python program to determine the position of the characters in a string using index. We will provide the an example with explanation along with steps. At the end, you can find more detail about the build-in methods and functions used in the program.

Steps

Follow the below steps to determines the position of characters in a string using their index:

1. Start by defining a function named character_positions that takes an input_string as a parameter.

2. Create an empty dictionary named positions to store the characters and their indices.

3. Use a for loop along with the `enumerate` function to iterate through each character and its index in the input_string.

4. For each character, check if it already exists in the positions dictionary.
     If it exists, append the current index to the list of indices for that character.
     If it doesn't exist, create a new key-value pair in the dictionary with the character as the key and a list containing the current index as the value.

5. After processing all characters, return the positions dictionary from the function.

6. Outside the function, provide an example input string, like "hello".
    Call the character_positions function with the input string and store the result in a variable, say positions.

7. Use a for loop to iterate through the positions dictionary. Print each character along with its associated list of indices.

These steps outline how the program works to determine the positions of characters in a string using their indices. Try to follow these steps to understand the program's logic and modify it as needed.

Example (Python Program)

Below is a Python program that determines the position of characters in a string using their index:

def character_positions(input_string):
    positions = {}  # Step 2

    for index, char in enumerate(input_string):  # Step 3
        if char in positions:  # Step 4
            positions[char].append(index)
        else:
            positions[char] = [index]

    return positions  # Step 5

# Example usage
input_string = "hello"
positions = character_positions(input_string)  # Step 6

for char, indices in positions.items():  # Step 7
    print(f"Character '{char}' appears at positions: {indices}")

Output

Character 'h' appears at positions: [0] Character 'e' appears at positions: [1] Character 'l' appears at positions: [2, 3] Character 'o' appears at positions: [4]

Explanation

In this program, the character_positions function takes an input string and creates a dictionary called positions to store the characters and their corresponding indices. The enumerate function is used to iterate over the characters in the string along with their indices. If a character is already present in the positions dictionary, its index is appended to the existing list of indices. If the character is encountered for the first time, a new list with the current index is created.

The example usage demonstrates how to use the function with the input string "hello" and then prints out the positions of each character in the string.

Try to replace the input_string variable with any string you'd like to analyze.

Build-in Methods and Functions used in the Program

Below are a few built-in functions and methods used in the above program with explanation.

1. enumerate() Function

  • The enumerate() function is used to iterate through a sequence (in this case, the characters of the input string) while keeping track of both the index and the value of each item. It returns pairs of (index, value) for each item in the sequence.
  • In the program, enumerate(input_string) is used in the for loop to iterate through each character and its index in the input string.

2. dict() Constructor

  • The dict() constructor is used to create a dictionary. In the program, positions = {} initializes an empty dictionary named positions to store the characters and their positions.

3. append() Method

  • The append() method is used with lists to add an element at the end of the list.
  • In the program, when a character is already in the positions dictionary, the append() method is used to add the current index to the list of positions for that character.

4. in Keyword

  • The in keyword is used to check if a value is present in a container, such as a list, dictionary, or string.
  • In the program, the if char in positions: condition is used to check if a character is already a key in the positions dictionary.

5. items() Method

  • The items() method is used with dictionaries to return a list of key-value pairs.
  • In the program, positions.items() is used in the `for` loop to iterate through each key-value pair in the positions dictionary.

6. print() Function

  • The print() function is used to display text or values in the console.
  • In the program, print(f"Character '{char}' appears at positions: {indices}") is used to print the character and its corresponding positions.

These built-in functions and methods are utilized to make the program work effectively in finding and displaying the positions of characters in a string. 

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