Python – Read a file line-by-line

In this tutorial, we are going to see different ways to read a file line by line in Python.

Opening a file and reading its content is quite easy in Python. A simple way to read a text file is to use “readlines” on a File object.
 

Read all the lines of a file at once using readlines()

There are three ways to read all the lines in a file. First, we can use the readlines() function. Python’s readlines function reads all the contents of the text file and places them in a list of lines. Here is how to use Python’s readlines after opening the file.
 
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# Open file in read-only mode
file = open('file.txt', "r")
# use readlines to read all lines in the file
# "lines" is a list containing all the lines of the file
lines = file.readlines()
# close the file after reading the lines
file.close()

# Iterate through lines
for line in lines:
    print(line.strip())

Output:

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Pellentesque eu elit tempus nunc volutpat malesuada.
Pellentesque suscipit dui eget semper faucibus. Sed at facilisis odio. 
Mauris nec enim eros.

Do not forget to close the file manager (“file”) with file.close()
 
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Read a file line by line using the While loop

Here is how to read a text file line by line using the “While” loop and readline() function. Since we read one line at a time with readline, we can easily handle large files without worrying about memory problems.

# Open file in read-only mode
file = open('file.txt', "r")
# use readline() to read the first line
line = file.readline()

while line:
    print(line)
    # use readline () to read the next line
    line = file.readline()
file.close()

Output:

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Pellentesque eu elit tempus nunc volutpat malesuada.
Pellentesque suscipit dui eget semper faucibus. Sed at facilisis odio. 
Mauris nec enim eros.

 

Read a file line by line using an iterator

You can also use an iterator to read a text file line by line. Here is how to do it.

# Open file in read-only mode
file = open('file.txt', "r")
for line in file:
    print(line)
file.close()

Output:

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Pellentesque eu elit tempus nunc volutpat malesuada.
Pellentesque suscipit dui eget semper faucibus. Sed at facilisis odio. 
Mauris nec enim eros.

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