How to Read a Text File in Python 3.6

Python 3 - Files I/O

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This chapter covers all the bones I/O functions available in Python 3. For more functions, please refer to the standard Python documentation.

Printing to the Screen

The simplest way to produce output is using the impress statement where you tin pass zero or more expressions separated by commas. This office converts the expressions you pass into a string and writes the effect to standard output as follows −

#!/usr/bin/python3  print ("Python is actually a great language,", "isn't it?")        

This produces the following result on your standard screen −

Python is really a great language, isn't it?        

Reading Keyboard Input

Python 2 has 2 built-in functions to read data from standard input, which by default comes from the keyboard. These functions are input() and raw_input()

In Python 3, raw_input() function is deprecated. Moreover, input() functions read data from keyboard as string, irrespective of whether it is enclosed with quotes ('' or "" ) or non.

The input Function

The input([prompt]) role is equivalent to raw_input, except that it assumes that the input is a valid Python expression and returns the evaluated result to y'all.

#!/usr/bin/python3  >>> x = input("something:") something:ten  >>> x '10'  >>> x = input("something:") something:'10' #entered information treated every bit string with or without ''  >>> x "'10'"        

Opening and Closing Files

Until now, yous have been reading and writing to the standard input and output. Now, nosotros will run across how to use bodily data files.

Python provides bones functions and methods necessary to manipulate files by default. You tin can do most of the file manipulation using a file object.

The open Role

Earlier yous can read or write a file, you take to open information technology using Python'south built-in open up() part. This function creates a file object, which would be utilized to call other support methods associated with it.

Syntax

file object = open(file_name [, access_mode][, buffering])        

Hither are parameter details −

• file_name − The file_name argument is a string value that contains the name of the file that you lot want to access.

• access_mode − The access_mode determines the mode in which the file has to be opened, i.e., read, write, append, etc. A complete list of possible values is given below in the tabular array. This is an optional parameter and the default file access mode is read (r).

• buffering − If the buffering value is set to 0, no buffering takes place. If the buffering value is 1, line buffering is performed while accessing a file. If y'all specify the buffering value every bit an integer greater than 1, then buffering action is performed with the indicated buffer size. If negative, the buffer size is the system default(default behavior).

Here is a list of the different modes of opening a file −

Sr.No.	Way & Clarification
ane	r Opens a file for reading simply. The file arrow is placed at the get-go of the file. This is the default mode.
two	rb Opens a file for reading only in binary format. The file pointer is placed at the beginning of the file. This is the default mode.
three	r+ Opens a file for both reading and writing. The file arrow placed at the beginning of the file.
4	rb+ Opens a file for both reading and writing in binary format. The file pointer placed at the beginning of the file.
5	due west Opens a file for writing only. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.
six	wb Opens a file for writing only in binary format. Overwrites the file if the file exists. If the file does not be, creates a new file for writing.
seven	due west+ Opens a file for both writing and reading. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.
eight	wb+ Opens a file for both writing and reading in binary format. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing.
9	a Opens a file for appending. The file arrow is at the cease of the file if the file exists. That is, the file is in the suspend mode. If the file does not exist, it creates a new file for writing.
x	ab Opens a file for appending in binary format. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does non exist, information technology creates a new file for writing.
11	a+ Opens a file for both appending and reading. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing.
12	ab+ Opens a file for both appending and reading in binary format. The file pointer is at the cease of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing.

The file Object Attributes

Once a file is opened and you lot take one file object, yous can go various information related to that file.

Here is a list of all the attributes related to a file object −

Sr.No.	Attribute & Clarification
1	file.airtight Returns true if file is closed, false otherwise.
two	file.mode Returns access mode with which file was opened.
3	file.name Returns name of the file.

Note − softspace attribute is non supported in Python iii.x

Example

#!/usr/bin/python3  # Open a file fo = open("foo.txt", "wb") print ("Proper noun of the file: ", fo.name) print ("Closed or not : ", fo.closed) impress ("Opening mode : ", fo.style) fo.close()        

This produces the following result −

Proper noun of the file:  foo.txt Closed or not :  False Opening manner :  wb        

The close() Method

The close() method of a file object flushes any unwritten information and closes the file object, after which no more writing can be done.

Python automatically closes a file when the reference object of a file is reassigned to some other file. It is a adept practice to use the close() method to close a file.

Syntax

fileObject.close();        

Example

#!/usr/bin/python3  # Open a file fo = open("foo.txt", "wb") print ("Proper name of the file: ", fo.name)  # Close opened file fo.shut()        

This produces the post-obit result −

Name of the file:  foo.txt        

Reading and Writing Files

The file object provides a set of access methods to make our lives easier. We would see how to use read() and write() methods to read and write files.

The write() Method

The write() method writes any string to an open file. It is important to annotation that Python strings can accept binary data and non just text.

The write() method does not add a newline character ('\northward') to the end of the string −

Syntax

fileObject.write(string);        

Here, passed parameter is the content to be written into the opened file.

Example

#!/usr/bin/python3  # Open a file fo = open("foo.txt", "westward") fo.write( "Python is a great language.\nYeah its cracking!!\due north")  # Close opend file fo.close()        

The above method would create foo.txt file and would write given content in that file and finally it would shut that file. If yous would open this file, it would have the following content −

Python is a great language. Yeah its great!!        

The read() Method

The read() method reads a string from an open file. It is important to note that Python strings tin can take binary data. apart from text data.

Syntax

fileObject.read([count]);        

Hither, passed parameter is the number of bytes to be read from the opened file. This method starts reading from the commencement of the file and if count is missing, then it tries to read as much every bit possible, maybe until the end of file.

Example

Allow us take a file foo.txt, which we created to a higher place.

#!/usr/bin/python3  # Open up a file fo = open up("foo.txt", "r+") str = fo.read(10) print ("Read String is : ", str)  # Close opened file fo.close()        

This produces the following result −

Read String is :  Python is        

File Positions

The tell() method tells y'all the current position within the file; in other words, the side by side read or write will occur at that many bytes from the beginning of the file.

The seek(first[, from]) method changes the current file position. The first statement indicates the number of bytes to be moved. The from argument specifies the reference position from where the bytes are to exist moved.

If from is prepare to 0, the beginning of the file is used equally the reference position. If it is set to 1, the electric current position is used as the reference position. If it is set to ii then the end of the file would be taken as the reference position.

Case

Allow us take a file foo.txt, which nosotros created in a higher place.

#!/usr/bin/python3  # Open a file fo = open("foo.txt", "r+") str = fo.read(10) print ("Read String is : ", str)  # Check current position position = fo.tell() impress ("Current file position : ", position)  # Reposition arrow at the kickoff once once more position = fo.seek(0, 0) str = fo.read(10) print ("Once more read String is : ", str)  # Close opened file fo.close()        

This produces the following result −

Read String is :  Python is Current file position :  10 Again read String is :  Python is        

Renaming and Deleting Files

Python os module provides methods that help you perform file-processing operations, such as renaming and deleting files.

To use this module, you demand to import it first and then you can call any related functions.

The rename() Method

The rename() method takes ii arguments, the current filename and the new filename.

Syntax

os.rename(current_file_name, new_file_name)        

Case

Post-obit is an example to rename an existing file test1.txt −

#!/usr/bin/python3 import bone  # Rename a file from test1.txt to test2.txt os.rename( "test1.txt", "test2.txt" )        

The remove() Method

Yous can apply the remove() method to delete files by supplying the name of the file to be deleted as the argument.

Syntax

bone.remove(file_name)        

Case

Following is an example to delete an existing file test2.txt −

#!/usr/bin/python3 import os  # Delete file test2.txt os.remove("text2.txt")        

Directories in Python

All files are contained inside various directories, and Python has no trouble handling these too. The os module has several methods that aid you create, remove, and change directories.

The mkdir() Method

You can use the mkdir() method of the os module to create directories in the current directory. You lot demand to supply an argument to this method, which contains the name of the directory to be created.

Syntax

bone.mkdir("newdir")        

Example

Following is an example to create a directory test in the current directory −

#!/usr/bin/python3 import os  # Create a directory "test" os.mkdir("test")        

The chdir() Method

You tin use the chdir() method to change the current directory. The chdir() method takes an argument, which is the name of the directory that you want to make the electric current directory.

Syntax

os.chdir("newdir")        

Case

Following is an example to go into "/domicile/newdir" directory −

#!/usr/bin/python3 import os  # Changing a directory to "/home/newdir" bone.chdir("/abode/newdir")        

The getcwd() Method

The getcwd() method displays the current working directory.

Syntax

os.getcwd()        

Instance

Following is an instance to give current directory −

#!/usr/bin/python3 import bone  # This would give location of the current directory bone.getcwd()        

The rmdir() Method

The rmdir() method deletes the directory, which is passed every bit an statement in the method.

Earlier removing a directory, all the contents in it should be removed.

Syntax

os.rmdir('dirname')        

Example

Following is an instance to remove the "/tmp/test" directory. It is required to requite fully qualified name of the directory, otherwise it would search for that directory in the current directory.

#!/usr/bin/python3 import os  # This would  remove "/tmp/test"  directory. os.rmdir( "/tmp/examination"  )        

File and Directory Related Methods

There are iii important sources, which provide a wide range of utility methods to handle and dispense files & directories on Windows and Unix operating systems. They are as follows −

• File Object Methods

  The file object provides functions to manipulate files.

• OS Object Methods

  This provides methods to procedure files as well equally directories.

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Source: https://www.tutorialspoint.com/python3/python_files_io.htm

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