Python Readline Close File Then Read Next Line

What is Python readline?

Python readline() is a file method that helps to read one complete line from the given file. It has a trailing newline ("\n") at the end of the cord returned.

You lot can too make apply of the size parameter to get a specific length of the line. The size parameter is optional, and by default, the entire line will be returned.

The flow of readline() is well understood in the screenshot shown below:

Yous accept a file demo.txt, and when readline() is used, it returns the very get-go line from demo.txt.

How readline works

In this tutorial, you will learn:

• Python File readline
• Characteristic of Python readline()
• Syntax
• Example: To read the outset line using readline()
• Example: Using size argument in readline()
• Basic File IO in Python
• Read a File Line-by-Line in Python
• How to read all lines in a file at once?
• How to read a File line-past-line using for loop?
• How to read a File line-by-line using a while loop?

Feature of Python readline()

Here, are of import characteristics of Python read line:

• Python readline() method reads but one complete line from the file given.
• It appends a newline ("\north") at the end of the line.
• If you open the file in normal read mode, readline() volition render you the string.
• If you lot open up the file in binary mode, readline() volition return you lot binary object.
• Y'all tin can give size as an statement to readline(), and it will go you lot the line equally per the size given inclusive of the newline. Past default, the size is 0, and information technology returns the entire line.

Syntax

file.readline(size)          

Parameters

size: (optional) Here, y'all can specify the number, an integer value to readline(). It will get the string of that size. Past default, the value of size is -1, and hence the entire cord is returned.

ReturnValue

The readline() method returns the line from the file given.

Example: To read the showtime line using readline()

Here will understand how to read the line from the file given using the readline() method. Nosotros are going to make use of demo.txt file here to read the contents.

The file contents of demo.txt are as follows:

demo.txt

Testing - FirstLine Testing - SecondLine Testing - Third Line Testing - Fourth Line Testing - Fifth Line          

The following are the steps to read a line from the file demo.txt.

Footstep 1)

First, open the file using the file open() method, as shown below:

myfile = open("demo.txt", "r")          

The open up() method takes the first parameter as the name of the file, and the second parameter is the mode is while yous want to open. Right now, we have used "r", which means the file will open up in read manner.

Pace 2)

Employ the readline() method to read the line from the file demo.txt as shown beneath:

myline = myfile.readline()          

Footstep 3)

The line read is stored inside myline. Let us now print the line to see the details:

print(myline)          

Step 4)

In one case the reading is done, close the file using close() method as shown below:

myfile.close()          

The entire code is as follows:

myfile = open("demo.txt", "r") myline = myfile.readline() print(myline) myfile.close()          

Output:

Testing - FirstLine          

Example: Using size argument in readline()

Nosotros accept seen how to read the entire line from the file given. You can also brand use of the size parameter to go only the required length of the line.

The given instance has the size parameter given every bit ten. The first line will exist fetched, and it will return the line with characters from 0 to ten.

We are going to make use of demo.txt file used earlier. Save the file demo.txt and use the location of the demo.txt inside open() function.

myfile = open("demo.txt", "r") myline = myfile.readline(ten) impress(myline) myfile.close()          

Output:

Testing -          

Basic File IO in Python

The bones file IO in Python to open a file for reading or writing is the built-in open() function. The ii important arguments that goes in open() function are the file path, which is a string, and the fashion that specifies whether the file is meant for reading or writing. The mode argument is a string.

Syntax:

open("file path", "mode")          

Post-obit are the modes available that can be used with open() method:

Manner	Description
R	This will open() the file in read mode.
W	Using w, you can write to the file.
a	Using a with open() will open up the file in write mode, and the contents volition be appended at the cease.
rb	The rb mode will open the file for binary data reading.
wb	The wb mode volition open the file for writing binary data.

Since we demand the file for reading, we are going to make use of read mode i.e. (r).

Read a File Line-past-Line in Python

The readline() method helps to read just 1 line at a time, and information technology returns the get-go line from the file given.

Here, we volition make use of readline() to read all the lines from the file given. The file that will read is demo.txt. The contents of the file are:

Save the file demo.txt and apply the location of demo.txt within open() office.

Testing - FirstLine Testing - SecondLine Testing - Third Line Testing - Fourth Line Testing - Fifth Line          

Using readline() inside while-loop will take care of reading all the lines present in the file demo.txt.

myfile = open("demo.txt", "r") myline = myfile.readline() while myline:     print(myline)     myline = myfile.readline() myfile.close()          

Output:

Testing - FirstLine Testing - SecondLine Testing - Third Line Testing - Fourth Line Testing - Fifth Line          

How to read all lines in a file at once?

To read all the lines from a given file, you tin brand use of Python readlines() function. The specialty of Python readlines() function is to read all the contents from the given file and salvage the output in a listing.

The readlines() function reads until the End of the file, making use of readline() part internally and returns a list with all the lines read from the file.

Here is a working case to read all the lines from the file using readlines().

The file that we are going to make apply of to read is exam.txt. The contents of the file examination.txt are as follows:

examination.txt: Save the file exam.txt and employ the location of exam.txt inside open up() part.

Line No 1 Line No ii Line No 3 Line No four Line No v          

myfile = open("test.txt", "r") mylist = myfile.readlines() impress(mylist) myfile.shut()          

Output:

['Line No 1\n', 'Line No 2\northward', 'Line No 3\north', 'Line No iv\n', 'Line No 5']          

How to read a File line-by-line using for loop?

Post-obit are the steps to read a line-past-line from a given file using for-loop:

Step1 :

First, open the file using Python open up() function in read style.

Stride two:

The open up() part will render a file handler. Use the file handler inside your for-loop and read all the lines from the given file line-by-line.

Step 3:

Once done, close the file handler using the close() function.

Here is a working instance of using for-loop to read line-past-line from a given file. The file that we are going to utilize here is test.txt.

The contents of exam.txt are as shown below. Save the file test.txt and use the location of test.txt inside an open() function.

Line No 1 Line No two Line No three Line No 4 Line No 5          

myfile = open("exam.txt", "r") for line in myfile:     impress(line) myfile.close()          

Output:

Line No 1 Line No two Line No 3 Line No 4 Line No 5          

How to read a File line-by-line using a while loop?

You tin make use of a while loop and read the contents from the given file line-by-line. To practise that, commencement, open the file in read way using open() function. The file handler returned from open(), use it inside while –loop to read the lines.

Python readline() part is used within while-loop to read the lines. In the case of for-loop, the loop terminates when the end of the file is encountered. But the same is not the case with a while-loop, and yous need to proceed a check to see if the file is washed reading. So once the readline() function returns an empty cord, you can make use of the intermission argument to terminate from the while –loop.

Hither is a working example to read a file line past line using a while-loop.

The file that nosotros are going to brand utilise is test.txt .Save the file test.txt and use the location of test.txt inside open() function.

Line No 1 Line No ii Line No 3 Line No 4 Line No v          

myfile = open("test.txt", "r") while myfile:     line  = myfile.readline()     print(line)     if line == "":         interruption myfile.close()          

Output:

Line No 1 Line No 2 Line No iii Line No 4 Line No 5          

Summary

• Python readline() is a file method that helps to read one complete line from the given file. It has a trailing newline ("\n") at the end of the string returned.
• You lot tin can besides brand use of the size parameter to get a specific length of the line. The size parameter is optional, and by default, the entire line volition exist returned.
• The readline() method helps to read just ane line at a time, and it returns the starting time line from the file given. We will brand use of readline() to read all the lines from the file given.
• To read all the lines from a given file, you can brand apply of Python readlines() function. The specialty of Python readlines() function is that it reads all the contents from the given file and saves the output in a list.
• The readlines() role reads till the Stop of the file making use of readline() function internally and returns a list that has all the lines read from the file.
• It is possible to read a file line past line using for loop. To do that, first, open the file using Python open() function in read mode. The open() office will return a file handler. Use the file handler inside your for-loop and read all the lines from the given file line past line. Once done,close the file handler using shut() function.
• Yous tin make use of a while loop and read the contents from the given file line by line. To do that, first, open the file in read mode using open up() function. The file handler returned from open(), utilise it inside while –loop to read the lines. Python readline() function is used inside while-loop to read the lines.

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