Python Read Text File Line by Line into List

In Python programming language, reading a text file line by line into a list is a common task.

This article will guide you through the process of reading a text file line by line into a list in Python. We will cover the following topics:

    Table of Contents

  1. Why Read Text File Line by Line into List?
  2. Reading Text File Line by Line into List in Python
    1. Opening a Text File in Python
    2. Reading Text File Line by Line
    3. Appending Lines to a List
    4. Closing a Text File in Python
  3. Alternative Methods for Reading Text Files into List
    1. Using List Comprehension
    2. Using the with Statement
    3. Using readlines() Method
  4. Best Practices When Reading Text File Line by Line into List
  5. Conclusion

Why Read Text File Line by Line into List?

Reading a text file line by line into a list is useful in many scenarios, including:

Reading files line by line into a list allows for efficient memory usage, as it only loads one line at a time.

This is particularly useful when working with large files that cannot be loaded into memory all at once.

For example, if you have a text file with 1 million lines, you can read the file line by line into a list, and process each line one at a time.

Reading Text File Line by Line into List in Python

Here are the steps to read a text file line by line into a list in Python:

1. Opening a Text File in Python

To read a text file line by line into a list, we must first open the text file using Python's built-in open() function. The open() function takes two arguments: the file path and the mode.

file_path = "example.txt"
mode = "r"

with open(file_path, mode) as file:
    # Read file here

The with statement is used to ensure that the file is closed when the block inside the with statement is exited. The mode argument is set to "r" for reading mode.

2. Reading Text File Line by Line

Once the file is open, we can read it line by line using a for loop.

file_path = "example.txt"
mode = "r"

with open(file_path, mode) as file:
    lines = []
    for line in file:
        # Process line here

This code snippet reads each line of the file and appends it to the lines list after stripping any leading or trailing whitespace.

3. Appending Lines to a List

To store the lines in a list, we must first initialize an empty list before the for loop.

file_path = "example.txt"
mode = "r"

with open(file_path, mode) as file:
    lines = []
    for line in file:
        # Process line here

The append() method adds each line of the file to the lines list.

4. Closing a Text File in Python

After the file has been read, it is important to close the file using the close() method.

file_path = "example.txt"
mode = "r"

with open(file_path, mode) as file:
    lines = []
    for line in file:
        # Process line here
        lines.append(line.strip())
file.close()

Alternative Methods for Reading Text Files into List

There are several alternative methods for reading a text file line by line into a list in Python.

Using List Comprehension

List comprehension is a concise way of creating a list in Python. It can also be used to read a text file into a list.

file_path = "example.txt"
mode = "r"

with open(file_path, mode) as file:
    lines = [line.strip() for line in file]

This code snippet reads each line of the file, strips any leading or trailing whitespace, and creates a list of lines using list comprehension.

Using the with Statement

The with statement can also be used to read a text file into a list using the readlines() method.

file_path = "example.txt"
mode = "r"

with open(file_path, mode) as file:
    lines = file.readlines()
    lines = [line.strip() for line in lines]

This code snippet reads each line of the file, strips any leading or trailing whitespace, and creates a list of lines using list comprehension.

Using readlines() Method

The readlines() method reads the entire file and returns a list of lines.

file_path = "example.txt"
mode = "r"

with open(file_path, mode) as file:
    lines = file.readlines()
    lines = [line.strip() for line in lines]

This code snippet reads each line of the file, strips any leading or trailing whitespace, and creates a list of lines using list comprehension.

Best Practices

Here are some best practices to follow when reading a text file line by line into a list in Python:

Conclusion

In this article, we have discussed how to read a text file line by line into a list in Python.

We have covered several methods for achieving this task, including using list comprehension and the readlines() method. We have also provided best practices for reading text files into a list.

Happy Learning!😇