Wednesday, July 22, 2020

Python Files I/O (Read and Write Files in Python)



Hello guys! Welcome back to another section of my tutorial on Python. In this tutorial guide, we are going to be studying about the Python Files I/O. We are going to be looking into the basic I/O functions that are available in Python. For more functions, please kindly refer to the standard Python documentation.

Printing to the Screen

The easiest way to produce output is by making use of the print statement where you can pass zero or more expressions that are separated by commas. This function converts the expressions you pass into a string and writes the result into a standard output.

Example

Below is a simple example which demonstrates how to print an output to the screen -

#!/usr/bin/python

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

Output

This is going to produce the following result on your standard screen -

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


Reading Keyboard Input

Python program provides two built-in functions to read a line of text from a standard input, that comes from the keyboard by default. These functions are -

  • raw_input
  • input

The raw_input Function

Python's raw_input([prompt]) function reads one line from standard input and returns it as a string. 

#!/usr/bin/python

str = raw_input("Enter your input: ")
print "Received input is : ", str

Output

This prompts you to enter any string and it displays the same string on the screen. When i typed "Hello Python!", its result will be like this -

Enter your input: Hello Python
Received input is :  Hello Python

The Input Function

The Python's input([prompt]) function is equivalent to raw_input, except that it assumes the input is a valid Python expression and then gives back the evaluated result to you -

#!/usr/bin/python

str = input("Enter your input: ")
print "Received input is : ", str

Output

When the above code is executed, it produces the following result against the entered input -

Enter your input: [x*5 for x in range(2,10,2)]
Recieved input is :  [10, 20, 30, 40]

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Opening and Closing Files 

Until now, you have been reading as well as writing to the standard input and output. Now we will learn how to use actual data files. 

Python provides basic functions and methods necessary in manipulating files by default. You can do most file manipulation using a file object.

The open Function

Before being able to read or write a file, you will have to open it using the Python's built-in open() function. This function creates a file object, which will be utilized to call other support methods which are associated with it.

Syntax

Below is the syntax of Python open() function -

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

Parameter Details

  • file_name - The file_name argument is a string value that contains the name of the file that you want to access.
  • access_mode - access_mode decides the mode in which the file has to be opened, that is read, write, append, and so on. A full list of possible values is given below in the table. It is an optional parameter and the default mode of accessing files is read (r).
  • buffering - If buffer value is set to 0, then no buffering takes place. If the buffering value is 1, line buffering is performed while accessing the file. If the buffering is been specified as integer than 1, then the buffer action will be performed with the indicated buffer size. If negative, the buffer size is the system's default.


Below is a list of the various modes of opening a file -

Sr.No.Modes & Description
1
r
Opens a file for reading only. The file pointer is placed at the beginning of the file. This is the default mode.
2
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.
3
r+
Opens a file for both reading and writing. The file pointer 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
w
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.
6
wb
Opens a file for writing only in binary format. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing.
7
w+
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.
8
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 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 not exist, it creates a new file for writing.
10
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 not exist, it 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 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.

The file Object Attributes

Once a file is opened and you have 1 file object, you can get the different informations that are related to that file -

Below is the list of attributes related to the file object -

Sr.No.Attribute & Description
1
file.closed
Returns true if file is closed, false otherwise.
2
file.mode
Returns access mode with which file was opened.
3
file.name
Returns name of the file.
4
file.softspace
Returns false if space explicitly required with print, true otherwise.


Example

Following below is a simple example -

#!/usr/bin/python

# Open a file
fo = open("foo.txt", "wb")
print "Name of the file: ", fo.name
print "Closed or not : ", fo.closed
print "Opening mode : ", fo.mode
print "Softspace flag : ", fo.softspace

Output

When the above code is executed, it will produce the following result -

Name of the file:  foo.txt
Closed or not :  False
Opening mode :  wb
Softspace flag :  0


The close() Method 

The close() method of the file object flushes away un-written information and closes the file object, after which no more writing can be made.

Python will automatically close a file when the reference object of a file is re-assigned to some other file. It is a very good practice to use the close() method to close a file.

Syntax

Following is the syntax of the close() method -

fileObject.close()

Example

Following below is a simple example -

#!/usr/bin/python

# Open a file
fo = open("foo.txt", "wb")
print "Name of the file: ", fo.name

# Close opend file
fo.close()

Output

When the above code is executed, it will produce the following result -

Name of the file:  foo.txt



Reading and Writing Files

The file object provides us with a set of access methods to make your life more easier. We will be discussing about how to make use of the read() and write() methods in reading and writing files.

The Write() Method

The write() method writes any string to an open file. It is so important to note that Python strings can have binary data and not just text.

Python write() method does not add a newline character ('\n') to the end of the string.

Syntax

fileObject.write(string)

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

Example

Following below is a simple example -

#!/usr/bin/python

# Open a file
fo = open("foo.txt", "wb")
fo.write( "Python is a great language.\nYeah its great!!\n")

# Close opend file
fo.close()

Output

The above method would create the foo.txt file and would write given content in that file and finally it would close that file. If you open this file, it will 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 so important to note that Python strings can have binary data aside from text data.

Syntax

fileObject.read([count])

Here, the passed parameter is the number of bytes to be read from the opened file. This method will start reading from the beginning of the file and if count is missing, then it tries to read as much as possible, maybe until the end of the file.

Example

Let us take a file foo.txt, which we created above -

#!/usr/bin/python

# Open a file
fo = open("foo.txt", "r+")
str = fo.read(10);
print "Read String is : ", str
# Close opend file
fo.close()

Output

When the above code is executed, it will produce the following result -

Read String is :  Python is

File Positions

The tell() method tells you the current position in the file. In other words, the next read or write will occur at that many bytes from the beginning of the file.

Seek(offset[, from]) method changes the current file position. The offset argument indicates the number of bytes that is to be moved. The from argument specifies the reference position from where the bytes are to be moved.

If from is set to 0, it means use the beginning of the file as the reference position. If set to 1, then it means use the current position in the file as the reference position and if set to 2, the end of the file would be taken as the reference position.

Example

Let's take a file foo.txt, which we created above -

#!/usr/bin/python

# Open a file
fo = open("foo.txt", "r+")
str = fo.read(10)
print "Read String is : ", str

# Check current position
position = fo.tell()
print "Current file position : ", position

# Reposition pointer at the beginning once again
position = fo.seek(0, 0);
str = fo.read(10)
print "Again read String is : ", str
# Close opend file
fo.close()

Output

When the above code is executed, it will produce the following result -

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

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Renaming and Deleting Files

Python os module provides methods which help to perform file-processing operations, such as to rename and delete files.

In order to use this module you need to import it first and then you can call any related functions.

The rename() Method

Python's rename() method takes two arguments, the current filename and the new filename.

Syntax

os.rename(current_file_name, new_file_name)

Example

Following is the example to rename an existing file test1.txt -

#!/usr/bin/python
import os

# Rename a file from test1.txt to test2.txt
os.rename( "test1.txt", "test2.txt" )

The remove() Method
You can use the remove() method to delete files by supplying the name of the file which is to be deleted as the argument.

Syntax
os.remove(file_name)

Example
Following is the example to remove an existing file text2.txt -

#!/usr/bin/python
import os

# Delete file test2.txt
os.remove("text2.txt")

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Directories in Python
All files are contained within various directories in Python, and Python has no problem handling these too. The os module has different types of methods that help to create, remove, and change directories.

The mkdir() Method
You can use the mkdir() method of the os module in creating directories in the current directory. You need to supply an argument to this method which contains the name of the directory to be created.

Syntax
os.mkdir("newdir")

Example
Following is an simple example to create a directory test in a directory -

#!/usr/bin/python
import os

# Create a directory "test"
os.mkdir("test")

The chdir() Method
You can use the chdir() Method of the os module in changing the current directory. The chdir() method takes an argument, which is the name of the directory that you want to make the current directory.

Syntax
os.chdir("newdir")

Example
Following below is a simple example to go into "home/newdir" directory -

#!/usr/bin/python
import os

# Changing a directory to "/home/newdir"
os.chdir("/home/newdir")

The getcwd() Method
The getcwd() method displays the current working directory.

Syntax
os.getcwd()

Example
Following is a simple example to give current directory -

#!/usr/bin/python
import os

# This would give location of the current directory
os.getcwd()

The rmdir() Method
Python's rmdir() method deletes the directory, which is passed as an argument in the method.

Before removing a directory, all the content in it should be removed.

Syntax
os.rmdir('dirname')

Example
Following is an example to remove "/tmp/test" directory. It is required that you give a complete qualified name of the directory, else it is going to search for that directory in the current directory.

#!/usr/bin/python
import os

# This would  remove "/tmp/test"  directory.
os.rmdir( "/tmp/test"  )

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File and Directory Related Methods
There are three important sources, that provides a wide range of utility methods to handle & also manipulate files & directories on Windows and Unix operating systems. They are as follows -


Alright guys! This is where we are rounding up for this tutorial guide. In my next tutorial, we are going to be discussing about Python File Object Methods.

Feel free to ask your questions where necessary and i will attend to them as soon as possible. If this tutorial was helpful to you, you can use the share button to share this tutorial.

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Thanks for reading and bye for now.
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