Reading a file line by line into a list can be a common task in Python when dealing with text files. This process allows you to easily access and manipulate the contents of the file. In this answer, we will explore different approaches to achieve this task.
Method 1: Using a For Loop
One way to read a file line by line into a list is by using a for loop. Here’s an example:
lines =  with open("file.txt", "r") as file: for line in file: lines.append(line.strip())
In this example, we open the file using the
open() function and specify the mode as “r” for reading. The file is then assigned to the variable
file. We use a for loop to iterate over each line in the file, and the
strip() method is used to remove any leading or trailing whitespace from each line. Each line is then appended to the
Method 2: Using List Comprehension
Another approach to read a file line by line into a list is by using list comprehension. Here’s an example:
with open("file.txt", "r") as file: lines = [line.strip() for line in file]
In this example, we use a list comprehension to create a new list called
strip() method is applied to each line to remove any leading or trailing whitespace. This approach is concise and often preferred when working with smaller files.
When reading a file line by line into a list in Python, it’s important to keep a few best practices in mind:
1. Use the
with statement: The
with statement ensures that the file is properly closed after reading, even if an exception occurs. It is considered best practice when working with files.
2. Handle file encoding: If you are working with files that have non-ASCII characters, specify the appropriate encoding when opening the file. For example,
with open("file.txt", "r", encoding="utf-8") as file:.
3. Handle large files: If you are working with large files that may not fit into memory, consider using a generator instead of creating a list. A generator allows you to iterate over the lines of a file without loading the entire file into memory at once.
4. Error handling: Always handle potential errors when reading a file, such as file not found or permission denied. You can use try-except blocks to catch and handle exceptions appropriately.
If you need to read a file line by line into a list but want to exclude empty lines or lines containing specific characters, you can modify the above examples accordingly. Here’s an example that excludes empty lines:
with open("file.txt", "r") as file: lines = [line.strip() for line in file if line.strip()]
In this example, the
if line.strip() condition is added to the list comprehension to exclude empty lines from the resulting list.