How to Read File Line by Line Into Python List

Python allows you to work with files and store its data into different data structures such as lists, dictionaries, tuples, etc. In this article, we will learn how to read file line by line and store each line as an item in list. In this article, we will learn how to read file line by line into python list.

How to Read File Line by Line Into Python List

There are several ways to read files line by line and store each line as a list item in python.

Here is the simple command to open file and load it completely into memory as a list named lines. readlines() function returns a list with each line as a separate item.

with open(filepath) as file:
    lines = file.readlines()

Here is an example to load contents of /home/ubuntu/data.txt into memory.

with open('/home/ubuntu/data.txt') as file:
    lines = file.readlines()

If you want to remove whitespace and newline characters from end of each line in the file, modify the above code as shown below.

with open(filepath) as file:
    lines = [line.rstrip() for line in file]

In the above use case, if you want to remove only newline characters but retain whitespace characters at the end of each line, you can modify the above code as shown.

with open(filepath) as f:
    lines = [line.rstrip('\n') for line in f]

If you are working with large files, the above code may overwhelm your system, since it loads the entire file into memory. In such cases, it is advisable to read and process the file line by line.

file_list=[]
with open(filepath) as file:
    for line in file:
        file_list.append(line.rstrip())

If you are using python 3.8+, you can also use while loop as shown below.

file_list=[]
with open(filepath) as file:
    while line := file.readline():
        file_list.append(line.rstrip())

In this article, we have learnt how to read files line by line in python and append each line to a list. You can use it as a part of a bigger function or module, or modify it as per your requirement.

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