This chapter covers all the basic I/O functions available in Python. For more functions, please refer to standard Python documentation.
Printing to the Screen
The simplest way to produce output is using the print statement where you can pass zero or more expressions separated by commas. This function converts the expressions you pass into a string and writes the result to standard output as follows −
#!/usr/bin/python
print "Python is really 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 provides two built-in functions to read a line of text from standard input, which by default comes from the keyboard. These functions are −
- raw_input
- input
This prompts you to enter any string and it would display same string on the screen. When I typed "Hello Python!", its output is like this −
Enter your input: Hello Python Received input is : Hello Python
Opening and Closing Files
Until now, you have been reading and writing to the standard input and output. Now, we will see how to use actual data files.
Python provides basic functions and methods necessary to manipulate files by default. You can do most of the file manipulation using a file object.
The open Function
Before you can read or write a file, you have to open it using Python's built-in open() function. 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])
Here are 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 − 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 table. This is 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 you specify the buffering value as 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. | 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 one file object, you can get various information related to that file.
Here is a list of all attributes related to 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#!/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
This produces 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 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 another file. It is a good practice to use the close() method to close a file.
Syntax
fileObject.close()
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 note that Python strings can have binary data and not just text.
The write() method does not add a newline character ('\n') to the end of the string −
Syntax
fileObject.write(string)
The read() Method
The read() method reads a string from an open file. It is important to note that Python strings can have binary data. apart from text data.
Syntax
fileObject.read([count])
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 need to import it first and then you can call any related functions.
The rename() Method
The rename() method takes two arguments, the current filename and the new filename.
Syntax
os.rename(current_file_name, new_file_name)
The remove() Method
You can use the remove() method to delete files by supplying the name of the file to be deleted as the argument.
Syntax
os.remove(file_name)
Do you Know?
Progamming is what actually means ?What is software development ?
How we categorized software development in different manner.
C Plus Plus
Python
Java Development
Web Designing
Javascript
Mysql
Oracle
