In This Article
One of the most common operations when working with data is input and output in Python, which involves reading data from files or writing data to files.
There are several ways to perform input and output operations, including using the built-in open() function Python to read and write to file.
File input output is an essential part of Python programming, as it enables us to work with large amounts of data that may not fit into memory.
Additionally, it allows us to store data for later use, share data between programs, and access data from external sources.
In this article post, we will explore the basics of file input output in Python and how to read and write files using the open() function. We will also discuss some of the common file IO methods, including reading and writing data, and manipulating file pointers.
Opening Files in Python
Opening Files in Python is done using the built-in
open() function, which returns a file object that can be used to read from or write to the file.
The syntax for
open() function is as follows:
file = open(filename, mode)
Here, filename is a string that specifies the name of the file we want to open, and mode is a string that specifies the mode in which we want to open the file.
The mode parameter is optional and defaults to ‘r‘, which means opening the file in read mode.There are several modes in which we can open a file:
'r': Read mode. The file is opened for reading (default).
'w': Write mode. The file is opened for writing. If the file already exists, its contents will be truncated. If the file does not exist, a new file will be created.
'a': Append mode. The file is opened for writing, and data is appended to the end of the file.
'x': Exclusive creation mode. The file is opened for writing, but only if it does not already exist.
'b': Binary mode. The file is opened in binary mode, which is used for non-text files like images or audio files.
't': Text mode. The file is opened in text mode, which is used for text files (default).
Once we have opened a file, we can read from or write to a file using methods like
Remember to always close the file after we are done working with it by calling the
close() method on the file object. Failure to close files can lead to resource leaks and unexpected behavior.
Python Read File
In Python, we can read the text of a file using the
readlines() method of a file object returned by the
Python read text from file
read() method reads the entire contents of a file as a single string.
For example, if we have a file named
example.txt containing the text “Hello, World!”, we can read its contents as follows:
file = open('example.txt', 'r') contents = file.read() print(contents) file.close() #output: Hello, World!
Python read file line
readline() method reads a single line from a file. If we call it repeatedly, it will continue reading lines until the end of the file is reached.
Example of Python reading a file line by line:
file = open('example.txt', 'r') line = file.readline() print(line) file.close() #output: Hello, World!
Python readlines- Read file line by line
readlines() method reads all the lines of a file and returns them as a list of strings.
Example of :
file = open('example.txt', 'r') lines = file.readlines() print(lines) file.close() #output: ['Hello, World!\n']
Remember to always close the file after reading its contents by calling the
close() method on the file object.
Alternatively, we can use a
with statement to automatically close the file after reading.
with open('example.txt', 'r') as file: contents = file.read() print(contents)
This is a safer and more concise way of working with files, as it ensures that the file is always closed, even if an error occurs while reading its contents.
Closing Files in Python
In Python, it’s important to properly close files after we’re done working with them.
Failing to do so can lead to resource leaks, which can slow down our program and potentially cause other issues.
Fortunately, closing a file in Python is quite simple.
To close a file in Python, we can call the
close() method on the file object that we opened.
file = open('example.txt', 'r') # do some stuff with the file file.close()
This will close the file and release any resources that were being used to keep it open. It’s a good practice to always close files when we’re done working with them.
However, sometimes we might forget to close a file or an error might occur before we have a chance to close it. To ensure that a file is always closed, we can use a
with statement to automatically close the file after we’re done working with it. For example:
with open('example.txt', 'r') as file: # do some stuff with the file # the file will automatically be closed here
with statement creates a context in which the file is opened and used. When the context is exited (either normally or due to an exception), the file is automatically closed.
This approach is safer than manually closing files, as it ensures that the file will always be properly closed even if an error occurs.
In summary, always remember to close our files after we’re done working with them, either by calling
close() explicitly or by using a
with statement to automatically close them. This will help prevent resource leaks and ensure that our program runs efficiently.
Exception Handling in Python Files read/write
When working with files in Python, it’s important to be aware of potential errors that can occur while reading from or writing to files.
These errors can include file not found errors, permission errors, and others.
To handle these errors, we can use exception handling.
In Python, exceptions are raised when an error occurs. We can use the
except statements to catch exceptions and handle them appropriately.
For example, consider the following Python code that tries to read from a file:
try: file = open('example.txt', 'r') contents = file.read() print(contents) except FileNotFoundError: print('File not found') finally: file.close()
Here, we try to open a file named
example.txt and read its contents.
FileNotFoundError exception is raised (indicating that the file was not found), we print an error message. Finally, we close the file using the
finally statement to ensure that it’s always properly closed, regardless of whether an exception occurred or not.
Handel Multiple Exception while Read & Write files in Python
We can also catch multiple exceptions by listing them in the
except statement, like this:
try: file = open('example.txt', 'r') contents = file.read() print(contents) except (FileNotFoundError, PermissionError): print('Error accessing file') finally: file.close()
Here, we catch both
PermissionError exceptions, which are both possible errors when opening and reading a file.
In addition to handling exceptions when opening and reading files, we can also handle exceptions when writing to files, closing files, and performing other file-related operations.
By using exception handling, we can ensure that our program gracefully handles errors and continues running, rather than crashing or producing unexpected results.
Useful Methods in Python for File Read Write
Python provides several methods for working with file input output.
Here are some of the most commonly used methods for file IO operations:
open(): This function is used to open a file and it returns a file object. We can specify the mode in which the file should be opened, such as
'w'for writing, or
close(): This method is used to close a file that was opened using
open(). It’s important to close files when we’re done working with them to free up system resources.
read(): This method is used to read the contents of a file. We can read the entire file as a string or specify the number of bytes to read.
write(): This method is used to write data to a file. We can write a single string or a list of strings.
readline(): This method is used to read a single line from a file.
readlines(): This method is used to read all the lines of a file and return them as a list of strings.
tell(): This method is used to get the current position of the file pointer, which indicates where the next read or write operation will occur.
seek(): This method is used to set the position of the file pointer. We can specify an offset from the beginning, end, or current position of the file.
flush(): This method is used to flush the internal buffer of a file, which ensures that all data that was written to the file is actually written to disk.
truncate(): This method is used to truncate a file to a specified size. Any data beyond the specified size will be deleted.
Working with files is an essential part of programming, and Python provides a simple and powerful set of tools for performing file input/output (I/O) operations.
By using the
write(), and other file methods, we can read and write data to files, manipulate file pointers, and manage file resources.
It’s important to keep in mind some best practices when working with files in Python, such as always closing files when we’re done working with them, handling exceptions that may occur during file operations, and using the appropriate mode when opening files (such as read mode for reading files and write mode for writing files).
Overall, understanding file input output operations in Python is an important skill for any developer who needs to work with data stored in files, such as reading data from configuration files or writing data to log files.