Python file lines to listen

Read a file line by line in Python

In this Python tutorial, we will learn, how to read a file line by line in Python with a few examples.

There are five methods to read a file line by line in Python, which are shown below:

• Using for loop
• Using readline()
• Using readlines() method
• Using a For Loop and List Comprehension
• Using the iter() with the next() Function

Python read a file line by line

Reading a file line by line is a common task in many Python programs, especially those that deal with large files. There are several methods that can be used to read a file line by line in Python.

Method-1: Python read a file line by line using for loop

This is the simplest method to read a file line by line in Python. It uses a for loop to iterate through the file object, which automatically reads the file one line at a time. This method is easy to understand and use, and it’s a good choice if you just need to process each line of the file one by one.

Open any text editor and write the lines as shown in the above picture and save the file with an extension (.txt). Now use the below code to read the file line by line.

# Open a file named 'python.txt' using a 'with' statement to ensure it's properly closed with open('python.txt') as f: # Iterate over each line in the file and print it to the console for line in f: print(line) 

The above code opens a file named ‘python.txt’ and reads its content line by line.

• It does so using the built-in ‘open’ function in Python, with a ‘with’ statement to ensure that the file is properly closed when the block is exited.
• The code then iterates over each line in the file using a ‘for’ loop and prints each line to the console using the ‘print’ function.

Method-2: Python read a file line by line using readline()

This method reads each line of the file using the readline() method, which returns a single line of the file at a time. The method then uses a while loop to process each line until the readline() method returns an empty string, indicating the end of the file.

# Open a file named 'python.txt' in read mode using a 'with' statement with open('python.txt', 'r') as file: # Read the first line of the file line = file.readline() # Continue reading the file line by line using a 'while' loop while line: line = file.readline() # Print each line to the console print(line) 

The above code opens a file named ‘python.txt’ in read mode and reads its content line by line.

• It does so using the built-in ‘open’ function in Python, with a ‘with’ statement to ensure that the file is properly closed when the block is exited.
• The code then reads the first line of the file using the ‘readline’ method and enters a ‘while’ loop that continues to read the file line by line until it reaches the end. For each line, the code prints it to the console using the ‘print’ function.

Method-3: Python read a file line by line using readlines() method

This method reads the entire file into a list of strings using the readlines() method.

# Define a list of strings Line = ["Welcome\n","to\n","Pythonguides\n"] # Open a file named 'line.txt' in write mode file = open('line.txt', 'w') # Write the strings from the list to the file using the 'writelines' method file.writelines(Line) # Close the file file.close() # Re-open the file in read mode file = open('line.txt', 'r') # Read the contents of the file into a list of strings Lines = file.readlines() # Iterate over the list of strings and print each one to the console for line in Lines: print(line) 

The above code creates a list of strings and writes its contents to a file named ‘line.txt’ using the built-in ‘open’ function in Python.

• It writes the strings from the list to the file using the ‘writelines’ method and then closes the file.
• The code then reopens the file in read mode, reads its contents into a list of strings using the ‘readlines’ method, and iterates over the list to print each line to the console using the ‘print’ function.

Method-4: Python read a file line by line using a For Loop and List Comprehension

This method reads the entire file into a list of stripped strings using a combination of a for loop and list comprehension. The for loop is used to iterate through the file object and the list comprehension is used to create a new list of stripped lines.

# Open a file named 'python.txt' in read mode using a 'with' statement with open('python.txt', 'r') as file: # Read the contents of the file into a list of strings using a list comprehension lines = [line.strip() for line in file] 

The above code opens a file named ‘python.txt’ in read mode using a ‘with’ statement.

• It then reads the contents of the file into a list of strings using list comprehension. The ‘strip’ method is used to remove any leading or trailing whitespace from each line in the file.
• The resulting list contains one string element for each line in the file, with the strings separated by ‘\n’ characters.

Method-5: Python read a file line by line using the iter() with the next() Function

This method uses the iter() function to create an iterator object from the file object and then uses the next() function to read each line of the file one at a time. You can use a while loop to read each line of the file until the end of the file is reached.

# Open a file named 'python.txt' in read mode using a 'with' statement to ensure it's properly closed with open('python.txt', 'r') as file: # Create an iterator over the file's lines lines = iter(file) # Loop over the iterator until there are no more lines to read while True: try: # Get the next line from the iterator and print it after removing any leading or trailing whitespace line = next(lines) print(line.strip()) except StopIteration: # Exit the loop when there are no more lines to read break 

The above code opens a file in read mode, creates an iterator over the file’s lines, and loops over the iterator to read and print each line of the file after removing any leading or trailing whitespace. The ‘with’ statement ensures that the file is properly closed when the block is exited.

You may also like to read the following Python tutorials.

Conclusion

In this tutorial, we have learned about Python read a file line by line example, and also we have covered these methods:

• Using for loop
• Using readline()
• Using readlines() method
• Using a For Loop and List Comprehension
• Using the iter() with the next() Function

I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.

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How to Read a File Line by Line in Python

Dionysia Lemonaki

When coding in Python, there may be times when you need to open and read the contents of a text file.

Luckily enough, there are several ways to do this in Python.

The language has many built-in functions, methods, and keywords that you can use to create, write, read and delete text files.

In this article, you’ll learn the most common ways of reading a file. With the help of coding examples, you will know how to read a text file line by line.

Here is what we will cover:

How to Open a Text File Using the open() Function in Python

Before you start reading a text file in Python, you first need to open it.

To open a text file, use the built-in open() function.

The general syntax for the open() function looks like this:

The open() function accepts multiple arguments, but in this example, I’m focusing only on two: filename and mode .

Let’s break down the syntax.

The first required argument that the open() function accepts is filename , which represents the full path of the file name you want to open.

When specifying the path of the file you want to open, you need to be aware of where that file is located in your folder structure.

For example, if the text file you want to open and your current file with Python code are in the same folder, you only need to reference its name and extension.

Say you have a folder with the name projects .

Inside it, you have two files, main.py , which is the file where you write your Python code, and example.txt , which is the file you would like to open. That file contains the following contents:

I absolutely love coding! I am learning to code for free with freeCodeCamp! 

Both files are on the same level in the folder, so here is how you would reference example.txt when using the open() function:

The second optional argument that the open() function accepts is mode . It specifies whether you want to read ( «r» ), write ( «w» ), or append ( «a» ) to filename .

The default mode is the read ( «r» ) mode.

So, to open and read example.txt , you could optionally use «r» to represent the mode you want to use:

With that said, you don’t need to write the keyword mode .

Instead, you can omit it and only use the letter «r» — it would still have the same result:

Lastly, you can omit the letter «r» altogether as it is the default mode:

When you run the code from the example above, it doesn’t do anything.

You completed the first step, which is opening the text file, but you haven’t read it and seen its contents.

How to Read a Text File Using the read() Method in Python

To read the contents of example.txt , let’s first store the code we wrote in the previous section in a variable named file :

Then, let’s call the read() method on file and print the result to the console:

file = open("example.txt") print(file.read()) # output # I absolutely love coding! # I am learning to code for free with freeCodeCamp! 

Now, you can read the contents of example.txt !

The read() method reads all the contents as a single string, which is useful when working with smaller files that don’t have a lot of content in the text file.

With that said, the code above is missing something.

Once you have finished reading the text file, you need to close it. To do that, use the close() method. Make sure not to skip this step because forgetting to close the file may introduce bugs in your code!

file = open("example.txt") print(file.read()) # close file file.close() 

Now, closing the text file is a good practice, but it is something that you can easily forget to do — you may not always remember to call the close() method on the file.

There is an alternative available.

The with keyword ensures that the file is automatically closed upon code execution.

The general syntax for the with keyword when used with the open() function is the following:

with open("filename") as variable: # do something with variable 

So, here is how you would rewrite the code from the previous example using the with keyword instead of the close() method:

with open("example.txt") as file: print(file.read()) # output # I absolutely love coding! # I am learning to code for free with freeCodeCamp! 

How to Read a Text File Using the readline() Method in Python

If you want to read only one single individual line from a text file, use the readline() method:

with open("example.txt") as file: print(file.readline()) # output # I absolutely love coding! 

The text file example.txt has two lines inside it, but the readline() method only reads one line from the file and returns it.

The readline() method also adds a trailing newline character at the end of the string.

You can optionally pass a size argument to the readline() method, which specifies the length of the returned line and the maximum number of bytes it will read.

with open("example.txt") as file: print(file.readline(10)) # output # I absolute 

How to Read a Text File Using the readlines() Method in Python

The readlines() method reads all the lines from a file, going through the file line by line.

It then returns a list of strings:

with open("example.txt") as file: print(file.readlines()) # output # ['I absolutely love coding!\n', 'I am learning to code for free with freeCodeCamp!'] 

The readlines() method read all the lines in one go and stored each line from the text file as a single list item inside a list. The readlines() method also added a newline character \n at the end of each line.

How to Read a Text File Using a for Loop in Python

An alternative way of reading a file line by line in Python is using a for loop, which is the most Pythonic approach to reading a file:

with open("example.txt") as file: for item in file: print(item) # output # I absolutely love coding! # I am learning to code for free with freeCodeCamp! 

The open() function returns an iterable object.

The for loop gets paired with the in keyword — they iterate over the returned iterable file object and read each line inside it.

Conclusion

Hopefully, this article helped you understand how to read a file line by line in Python using the read() , readline() , and readlines() methods and a for loop.

Thank you for reading, and happy coding!

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