Number of Lines in a File in Python

File handling is one of the most critical operations in programming. Sometimes, we may need to count the number of lines in a file to perform any operation on it. In this article, we will see how we can count the number of lines in a file in python. 

Count Number of Lines in a File using the for loop in Python

The first way to count the number of lines in a file is to use a for loop to count all the newline characters in the file. 

For this, we will first open the file using the open() function in the read mode. After that, we will traverse through the file content and check for the newline character “\n”. We will keep the count of “\n” characters in a variable named numberOfLines.

After execution of the for loop, we will have the total number of lines in the variable numberOfLines. You can observe this in the following example.

myFile = open("sample.txt", "r")
text = myFile.read()
print("The content of the file is:")
print(text)
numberOfLines = 0
for character in text:
    if character == "\n":
        numberOfLines = numberOfLines + 1
print("The number of lines in the file is:")
print(numberOfLines)

Output:

The content of the file is:
This is line 1.
This is line 2.
This is line 3.
This is line 4.

The number of lines in the file is:
4

While counting the number number of lines, empty lines are also counted in this method. This is so because we are counting the newline characters. Hence, empty lines will also be considered a new line as the “\n” character is present there.

Count Number of Lines in a File using the split() method in Python

Instead of checking for newline characters, we can use the split() method to count the number of lines in  a file. The split() method, when invoked on a string, takes a separator as input argument and returns a list of substrings of the original string. 

In our program, we will use “\n” as the separator to split the text of the file at newlines. After that, we will determine the length of the output list using the len() function. In this way, we will find the number of lines in the text file.

myFile = open("sample.txt", "r")
text = myFile.read()
print("The content of the file is:")
print(text)
text_list = text.split("\n")
numberOfLines = len(text_list)
print("The number of lines in the file is:")
print(numberOfLines)

Output:

The content of the file is:
This is line 1.
This is line 2.
This is line 3.
This is line 4.
The number of lines in the file is:
4

Count Number of Lines in a File using the readlines() method in Python

The readlines() method, when invoked on a file object, returns a list of strings in the file. Each string consists of a newline. We can find the length of the output list to count the number of lines in the file as follows.

myFile = open("sample.txt", "r")
text_list = myFile.readlines()
numberOfLines = len(text_list)
print("The number of lines in the file is:")
print(numberOfLines)

Output:

The number of lines in the file is:
4

Conclusion

In this article, we have discussed three ways to count the number of lines in a file in python. To read more about files, you can read this article on file handling in python. You might also like this article on how to read a text file line by line in python.