Python readfile by lines

How to read File Line by Line in Python?

There are many ways to read a text file line by line in Python. You can read the lines to a list, or just access them one by one in a loop by iterating over the lines provided by some kind of iterator or calling a function on the file object.

In this tutorial, we will learn how to read a file line by line using readline() function, readlines() function, or file object, with the help of example programs.

Example 1: Read Text File Line by Line – readline()

In this example, we will use readline() function on the file stream to get next line in a loop.

Steps to use file.readline() function

Following are the steps to read file line by line using readline() function.

1. Read file in text mode. It returns a stream to the file.
2. Create an Infinite While Loop.
   1. During each iteration of the loop, read the next line from the file using readline().
   2. If the line is not empty, you have the next line. You can check this using if-not. Else, there are no more lines in the file, and we break the loop.

   Python Program

   #get file object file1 = open("sample.txt", "r") while(True): #read next line line = file1.readline() #check if line is not null if not line: break #you can access the line print(line.strip()) #close file file1.close

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   Example 2: Read Lines as List – readlines()

   readlines() function returns all the lines in the file as a list of strings. We can traverse through the list, and access each line of the file.

   In the following program, we shall read a text file, and then get the list of all lines in the text file using readlines() function. After that, we use For Loop to traverse these list of strings.

   Python Program

   #get file object file1 = open("sample.txt", "r") #read all lines lines = file1.readlines() #traverse through lines one by one for line in lines: print(line.strip()) #close file file1.close

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   Example 3: Read File Line by Line using File Object

   In our first example, we have read each line of file using an infinite while loop and readline() function. But, you can use For Loop statement on the file object itself to get the next line in the file in each iteration, until the end of file.

   Following is the program, demonstrating how we use for-in statement to iterate over lines in the file.

   Python Program

   #get file object file1 = open("sample.txt", "r") #traverse through lines one by one for line in file1: print(line.strip()) #close file file1.close

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   Summary

   In this tutorial of Python Examples, we learned how to read a text file line by line, with the help of well detailed python example programs.

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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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