File Handling in Python: Working with File I/O

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When we use any computer application, some data needs to be provided. Data is stored in computer's main memory (RAM) until the application is running. Thereafter, memory contents from RAM are erased.

We would like to store it in such a way that it can be retrieved whenever required in a persistent medium such as a disk file.

Python uses built-in input() and print() functions to perform standard input/output operations. Python program interacts with these IO devices through standard stream objects stdin and stdout defined in sys module.

The input() function reads bytes from a standard input stream device i.e. keyboard. Hence both the following statements read input from the user.

name = input() #is equivalent to import sys name = sys.stdin.readline()

The print() function on the other hand, sends the data towards standard output stream device, i.e., the display monitor. It is a convenience function emulating write() method of stdout object.

print (name) #is equivalent to import sys sys.stdout.write(name)

Any object that interacts with input and output steam is called File object. Python's built-in function open() returns a file object.

The 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 the 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 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 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).

File Opening Modes

Following are the file opening modes −

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	b Opens the file in binary mode
7	t Opens the file in text mode (default)
8	+ open file for updating (reading and writing)
9	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.
10	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.
11	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.
12	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.
13	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.
14	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.
15	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.
16	x open for exclusive creation, failing if the file already exists

Once a file is opened and you have one file object, you can get various information related to that file.

Example

# 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) fo.close()

It will produce the following output −

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




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