Python readline all file

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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   Read File in Python

   In this article, we’ll learn how to read files in Python.

   In Python, temporary data that is locally used in a module will be stored in a variable. In large volumes of data, a file is used such as text and CSV files and there are methods in Python to read or write data in those files.

   After reading this tutorial, you’ll learn: –

   • Reading both text and binary files
   • The different modes for reading the file
   • All methods for reading a text file such as read() , readline() , and readlines()
   • Read text file line by line
   • Read and write files at the same time.

   Table of contents

   Access Modes for Reading a file

   To read the contents of a file, we have to open a file in reading mode. Open a file using the built-in function called open() . In addition to the file name, we need to pass the file mode specifying the purpose of opening the file.

   The following are the different modes for reading the file. We will see each one by one.

   

   # read file with absolute path try: fp = open(r"E:\demos\files\read_demo.txt", "r") print(fp.read()) fp.close() except FileNotFoundError: print("Please check the path")

   First line Second line Third line Fourth line Fifth line

   An absolute path contains the entire path to the file or directory that we need to access. It includes the complete directory list required to locate the file.

   For example, E:\PYnative\files_demos\read_demo.txt is an absolute path to discover the read_demo.txt. All of the information needed to find the file is contained in the path string.

   While opening a file for reading its contents we have always ensured that we are providing the correct path. In case the file not present in the provided path we will get FileNotFoundError .

   We can avoid this by wrapping the file opening code in the try-except-finally block.

   Reading a File Using the with Statement

   We can open a file using the with statement along with the open function. The general syntax is as follows.

   with open(__file__, accessmode) as f:

   The following are the main advantages of opening a file using ‘with’ statement

   • The with statement simplifies exception handling by encapsulating common preparation and cleanup tasks.
   • This also ensures that a file is automatically closed after leaving the block.
   • As the file is closed automatically it ensures that all the resources that are tied up with the file are released.

   Let us see how we can the with statement to read a file.

   # Reading files using 'with' with open('read_demo.txt', 'r') as file: print(file.read())

   First line Second line Third line Fourth line Fifth line

   File Read Methods

   Python provides three different methods to read the file. We don’t have to import any module for that.. Below are the three methods

   

   Reading File in Reverse Order

   We can read the contents of the file in reverse order by using the readlines() method and then calling the reversed () method on the list to get the contents of the list in reverse order. We can then iterate over the contents of the list and print the values.

   with open('readdemo.txt', 'r') as f: lines = f.readlines() for line in reversed(lines): print(line)

   Fifth Line Fourth Line Third Line Second Line First Line

   Reading a Binary file

   Binary files are basically the ones with data in the Byte format (0’s and 1’s). This generally doesn’t contain the EOL(End of Line) so it is important to check that condition before reading the contents of the file.

   We can open and read the contents of the binary file using the ‘with’ statement as below.

   with open("Timezones.jpg", "rb") as f: byte_content = f.read(1) while byte_content: #Printing the contents of the file print(byte_content)

   We have seen in this post how the file contents could be read using the different read methods available in Python. We also saw few simple examples to read the contents partially like first few lines or last few lines based on our requirement.

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   About Vishal

   I’m Vishal Hule, Founder of PYnative.com. I am a Python developer, and I love to write articles to help students, developers, and learners. Follow me on Twitter

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