Python Opening Closing Files

Python provides several built-in functions for creating, reading, writing files. You don’t need a third-party module to work with files.

To access a file for reading or writing, you need the following sequence of operations:

• Opening File
• Reading/Writing File
• Closing File

Opening File

To read or write a file in Python, you need to call built-in open() function. open() function returns a file object and it takes two arguments: filename and mode.

Syntax for open() function is given below.

open(filename, mode="r")

mode argument indicates how the file is accessed. "r" indicates the file is accessed in read-only mode, "w" is used for write mode, "a" is used for append mode.

Python File Opening Modes

File opening modes in Python are listed as follows:

Text/Binary Modes

There are 2 types of files: text files and binary files. A text file contains lines of human-readable plain-text strings, whereas a binary file contains unreadable sequence of bytes. Special software is required to process a binary file and interpret its data. .jpg, .mp3, .pdf, .exe files are examples of binary files.

Examples

Opening a File for Writing

To open a text file for writing you need to pass the mode argument as wt. Since text mode is the default mode, you can only pass w.

# opening a text file
my_file = open("demo_file.txt", "wt")  # or
my_file = open("demo_file.txt", "w")

# opening a binary file
my_file = open("demo_file.txt", "wb")

Opening a Text File for Reading

Both reading and text modes are default, so you don’t need to specify a mode argument.

my_file = open("demo_file.txt")

To open a file in read-only mode, the file should exist. If demo_file.txt does not exist, Python will give the following error.

FileNotFoundError: [Errno 2] No such file or directory: 'demo_file.txt' 

Writing vs Appending

Consider demo_file.txt file has the following contents.

demo_file.txt
This is the first line of the demo file
This is the second line of the demo file 

In Append mode, what you write is appended to the end of the file.

my_file = open("demo_file.txt", "a")
my_file.write("This the new line")
my_file.close()

demo_file.txt
This is the first line of the demo file
This is the second line of the demo file
This is the new line 

In Write mode, file is truncated to zero length and overwritten.

my_file = open("demo_file.txt", "w")
my_file.write("This the new line")
my_file.close()

demo_file.txt
This is the new line  

Closing File

When we finish reading or writing a file, we need to properly close the file.

Closing a file frees up the resources allocated for file access.

Closing a file is also important for not losing your work. Changes you have made in a file may not be written to disk until they are flushed. Python flushes everything on buffer to the file on disk when you close the file.

To close a file you can use a try/finally block. It’s a good idea to close the file in finally block to ensure the file is properly closed even if there is an exception in try block.

try:
    my_file=open("demo_file.txt", "a")
    my_file.write("This is the new line")
finally:
    my_file.close()

For cleaner code, you can use with statement to close files in Python. After executing with block, close() method is called implicity.

with open("demo_file.txt", "a") as my_file:
    my_file.write("This is the new line")