Skip to main content

How to Read Files Character by Character in Python

While less common than reading line by line, reading a file character by character in Python is sometimes necessary, especially when dealing with specific file formats or parsing tasks.

This guide explains how to read a file one character at a time using a while loop and file.read(1), and we'll discuss why using nested for loops to achieve this isn't efficient or Pythonic.

Reading Character by Character with a while Loop​

The most direct way to read a file one character at a time is to use a while loop and the file.read(1) method:

with open('example.txt', 'r', encoding='utf-8') as file:
    result = ''
    while True:
        char = file.read(1)  # Read one character

        if not char:  # End of file (empty string)
            print('Reached end of file')
            break

        print(char)
        result += char # Append to string, you can also add it to a list.
print(result) # Prints the contents of the file
  • with open(...) as file:: Opens the file in read mode ('r') with UTF-8 encoding (always specify encoding!). The with statement automatically closes the file.
  • while True:: This creates an infinite loop that we'll break out of when we reach the end of the file.
  • char = file.read(1): This is the key. file.read(1) reads one character from the file. If the end of the file is reached, it returns an empty string (''), not None.
  • if not char:: This is how we detect the end of the file. An empty string is "falsy," so not char is True when we're at the end.
  • break: Exits the while loop.
  • result += char: Appends the read character to the result string. You could also append to a list (my_list.append(char)) if you prefer a list of characters.
  • The file.read() takes an integer that represents how many bytes it will read from the file and returns them.

Adding Characters to a List​

If you want to store the characters in a list instead of a string:

with open('example.txt', 'r', encoding='utf-8') as file:
    characters = []

    while True:
        char = file.read(1)

        if not char:
            print('Reached end of file')
            break

        characters.append(char) # Append to list
        print(char)

    print(characters)  # Output: ['b', 'o', 'b', 'b', 'y', 'h', 'a', 'd', 'z', '.', 'c', 'o', 'm', '\n']

Why Nested for Loops Are Inefficient for Character-by-Character Reading​

You might see code like this:

with open('example.txt', 'r', encoding='utf-8') as file:
    for line in file:  # Reads line by line
        for char in line:  # Iterates through characters in the line
            print(char)
  • You should avoid using nested loops for reading a file.
  • This is much more efficient and concise, because Python file objects are iterable by line.

Table of Contents