Read One Line of a File at a Time Python
What is Python readline?
Python readline() is a file method that helps to read i consummate line from the given file. It has a trailing newline ("\northward") at the cease of the cord returned.
You can also brand use of the size parameter to go a specific length of the line. The size parameter is optional, and by default, the entire line will be returned.
The menstruum of readline() is well understood in the screenshot shown below:
Yous have a file demo.txt, and when readline() is used, it returns the very starting time line from demo.txt.
In this tutorial, y'all will learn:
- Python File readline
- Characteristic of Python readline()
- Syntax
- Instance: To read the first line using readline()
- Example: Using size argument in readline()
- Basic File IO in Python
- Read a File Line-past-Line in Python
- How to read all lines in a file at one time?
- How to read a File line-past-line using for loop?
- How to read a File line-past-line using a while loop?
Characteristic of Python readline()
Hither, are important characteristics of Python read line:
- Python readline() method reads just 1 complete line from the file given.
- It appends a newline ("\northward") at the end of the line.
- If you open up the file in normal read mode, readline() will return you the cord.
- If you open the file in binary mode, readline() will return you binary object.
- You can requite size as an statement to readline(), and information technology will become yous the line every bit per the size given inclusive of the newline. Past default, the size is 0, and it returns the entire line.
Syntax
file.readline(size)
Parameters
size: (optional) Here, you lot can specify the number, an integer value to readline(). Information technology will become the string of that size. By default, the value of size is -1, and hence the entire string is returned.
ReturnValue
The readline() method returns the line from the file given.
Instance: 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 hither to read the contents.
The file contents of demo.txt are as follows:
demo.txt
Testing - FirstLine Testing - SecondLine Testing - 3rd Line Testing - Fourth Line Testing - Fifth Line
The following are the steps to read a line from the file demo.txt.
Step 1)
Starting time, open up the file using the file open up() method, as shown beneath:
myfile = open("demo.txt", "r") The open() method takes the starting time parameter as the proper noun of the file, and the 2d parameter is the mode is while y'all want to open up. Correct now, we have used "r", which means the file will open up in read mode.
Footstep 2)
Employ the readline() method to read the line from the file demo.txt equally shown below:
myline = myfile.readline()
Pace three)
The line read is stored inside myline. Let us now impress the line to see the details:
print(myline)
Pace 4)
Once the reading is done, close the file using close() method as shown below:
myfile.close()
The entire code is every bit follows:
myfile = open("demo.txt", "r") myline = myfile.readline() impress(myline) myfile.close() Output:
Testing - FirstLine
Case: Using size statement in readline()
We have seen how to read the unabridged line from the file given. You can also brand employ of the size parameter to get only the required length of the line.
The given example has the size parameter given equally ten. The starting time line will be fetched, and information technology will render the line with characters from 0 to x.
We are going to make use of demo.txt file used earlier. Relieve the file demo.txt and utilize the location of the demo.txt inside open() function.
myfile = open up("demo.txt", "r") myline = myfile.readline(10) impress(myline) myfile.close() Output:
Testing -
Basic File IO in Python
The basic file IO in Python to open a file for reading or writing is the congenital-in open() role. The two important arguments that goes in open up() function are the file path, which is a string, and the way that specifies whether the file is meant for reading or writing. The way argument is a string.
Syntax:
open("file path", "mode") Following are the modes available that tin be used with open up() method:
| Mode | Description |
|---|---|
| R | This volition open() the file in read way. |
| W | Using westward, y'all tin write to the file. |
| a | Using a with open() will open the file in write mode, and the contents volition be appended at the end. |
| rb | The rb mode will open the file for binary data reading. |
| wb | The wb style will open the file for writing binary data. |
Since nosotros need the file for reading, we are going to brand use of read fashion i.e. (r).
Read a File Line-by-Line in Python
The readline() method helps to read but one line at a time, and it returns the showtime line from the file given.
Here, we will 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:
Relieve the file demo.txt and use the location of demo.txt inside open() function.
Testing - FirstLine Testing - SecondLine Testing - Tertiary 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 in one case?
To read all the lines from a given file, you tin make 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 list.
The readlines() function reads until the End of the file, making use of readline() function internally and returns a listing with all the lines read from the file.
Here is a working instance to read all the lines from the file using readlines().
The file that nosotros are going to make use of to read is test.txt. The contents of the file test.txt are every bit follows:
examination.txt: Relieve the file exam.txt and use the location of test.txt inside open() function.
Line No 1 Line No two Line No iii Line No 4 Line No 5
myfile = open up("test.txt", "r") mylist = myfile.readlines() impress(mylist) myfile.close() Output:
['Line No 1\n', 'Line No two\n', 'Line No 3\n', 'Line No iv\northward', 'Line No v']
How to read a File line-by-line using for loop?
Following are the steps to read a line-by-line from a given file using for-loop:
Step1 :
Outset, open up the file using Python open() part in read manner.
Pace 2:
The open() function volition return a file handler. Use the file handler within your for-loop and read all the lines from the given file line-by-line.
Step 3:
One time done, shut the file handler using the close() function.
Here is a working case of using for-loop to read line-by-line from a given file. The file that we are going to use here is examination.txt.
The contents of test.txt are as shown below. Save the file exam.txt and employ the location of test.txt within an open() function.
Line No one Line No two Line No three Line No four Line No v
myfile = open("examination.txt", "r") for line in myfile: impress(line) myfile.close() Output:
Line No ane Line No ii Line No 3 Line No 4 Line No v
How to read a File line-by-line using a while loop?
Yous can brand use of a while loop and read the contents from the given file line-by-line. To practise that, first, open the file in read mode using open up() function. The file handler returned from open(), employ it inside while –loop to read the lines.
Python readline() part is used inside while-loop to read the lines. In the case of for-loop, the loop terminates when the end of the file is encountered. Merely the same is non the case with a while-loop, and you need to go on a check to see if the file is done reading. And then once the readline() function returns an empty string, you can make use of the break statement 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 we are going to make use is examination.txt .Save the file test.txt and use the location of test.txt inside open() office.
Line No ane Line No 2 Line No 3 Line No 4 Line No 5
myfile = open("examination.txt", "r") while myfile: line = myfile.readline() print(line) if line == "": interruption myfile.close() Output:
Line No one Line No 2 Line No 3 Line No 4 Line No 5
Summary
- Python readline() is a file method that helps to read one consummate line from the given file. Information technology has a trailing newline ("\due north") at the end of the string returned.
- Yous tin can also brand use of the size parameter to get a specific length of the line. The size parameter is optional, and past default, the entire line volition be returned.
- The readline() method helps to read just one line at a time, and it returns the first line from the file given. Nosotros will brand use of readline() to read all the lines from the file given.
- To read all the lines from a given file, you lot can make utilize of Python readlines() office. The specialty of Python readlines() part is that it reads all the contents from the given file and saves the output in a list.
- The readlines() function reads till the Finish of the file making use of readline() role internally and returns a listing that has all the lines read from the file.
- Information technology is possible to read a file line past line using for loop. To do that, beginning, open up the file using Python open() part in read style. The open up() role will return a file handler. Apply the file handler inside your for-loop and read all the lines from the given file line by line. In one case done,close the file handler using shut() function.
- You tin can make utilise of a while loop and read the contents from the given file line past line. To do that, offset, open the file in read mode using open() part. The file handler returned from open(), use it within while –loop to read the lines. Python readline() role is used inside while-loop to read the lines.
Source: https://www.guru99.com/python-file-readline.html
0 Response to "Read One Line of a File at a Time Python"
Post a Comment