Python writing to file append

How to Append to a File in Python

How to append to a file in Python? Python makes it simple, open the file in append mode, append the data, and close the file. However, In this article, we will learn different methods for appending to a file in Python, including using the write() method, redirecting the output of the print() function to a file, and using a context manager to automatically close the file.

• Step1 – Check if the file exists in the specified Path & it has written permissions
• Step2 – Open the file in append mode
• Step3 – Append data to file
• Step4 – Close the file

1. Quick Examples of Appending to File

These quick examples will give a high-level overview of different ways to append to a file. We will discuss each method in more detail, later on.

2. Append to File in Python

Before appending text to a file, just make sure that the file is available, and that you have the operating system permission for appending the text. If the file is not available, python will create a new file and append the data.

Follow the following 3 steps to append data to a file in Python:

2.1 Step 1: Open the File in Append Mode

To append to a file in Python, you first need to open the file in append mode. You can do it with open() function. When opening the file, you should specify the file name and the mode in which you want to open the file. To open a file in append mode, use the ‘a’ mode.

2.2 Step 2: Write to the File

Once you open the file in append mode, you can write to the file using the write() method. This method allows you to write a string to the end of the file.

2.3 Step 3: Close the File

After you have finished appending to the file, it is important to close the file using the close() method. This will release any system resources that the file was using.

3. Complete Example of Appending Text to a File

This is a complete example of how to append text to a file. As explained above, to append text to a file in Python use the following steps:

• Open the file in append mode
• Write text to the file
• Close the file with close() function

4. Append to File with print() Function

Normally the print() function is used to print text to the console. However, You can also use the print() function to append to a file in Python. To do this, you simply need to specify the file parameter when calling the print() function, which tells Python to redirect the output to the specified file instead of the console.

5. “with” Context Manager

The with statement ensures that the file is closed automatically after the write operation, even if an exception is raised during the write operation. The with statement achieves this by using a context manager, which is a Python object that defines the runtime context for a block of code.

When the with statement is used with a file object, it automatically calls the file object’s __enter__() method to set up the context, and then calls the file object’s __exit__() method to tear down the context when the block of code is exited.

6. Example: Append at the Beginning of the File

We can use the seek() function to append at the beginning of the file. By default, the data is appended at the end of the file. The seek() function in Python is used to set the file pointer to a specific position in a file.

The offset argument is the number of bytes to move the file pointer. The whence argument specifies the reference point from which to start the offset.

See the below example that helps you to append data at the beginning of the file.

See more examples of the seek() function for appending data at different positions.

7. Summary and Conclusion

In this article, We have learned to append text to a file in Python with multiple approaches. You can append at the end of a file or insert content at a specific position. The seek() function can be used to move the file pointer to a specific position in the file. Hope this article was helpful. Leave questions in the comment section.

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Python append to a file

While reading or writing to a file, access mode governs the type of operations possible in the opened file. It refers to how the file will be used once it’s opened. These modes also define the location of the File Handle in the file. The definition of these access modes is as follows:

• Append Only (‘a’): Open the file for writing.
• Append and Read (‘a+’): Open the file for reading and writing.

When the file is opened in append mode in Python, the handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data.

Example 1: Python program to illustrate Append vs write mode.

Python3

Output of Readlines after appending This is Delhi This is Paris This is LondonToday Output of Readlines after writing Tomorrow

Example 2: Append data from a new line

In the above example of file handling, it can be seen that the data is not appended from the new line. This can be done by writing the newline ‘\n’ character to the file.

Python3

Output of Readlines after appending This is Delhi This is Paris This is London TodayTomorrow

Note: ‘\n’ is treated as a special character of two bytes.

Example 3: Using With statement in Python

with statement is used in exception handling to make the code cleaner and much more readable. It simplifies the management of common resources like file streams. Unlike the above implementations, there is no need to call file.close() when using with statement. The with statement itself ensures proper acquisition and release of resources.

Python3

Hello This is Delhi This is Paris This is London Today

Note: To know more about with statement click here.

Using the shutil module:

This approach uses the shutil.copyfileobj() method to append the contents of another file (source_file) to ‘file.txt’. This can be useful if you want to append the contents of one file to another without having to read the contents into memory first.

Approach:
The code uses the shutil.copyfileobj() function to copy the contents of the source_file object to a new file called file.txt. The with statement is used to open and automatically close the file, using the file object f.

Time Complexity:
The time complexity of shutil.copyfileobj() function is proportional to the size of the file being copied, as it needs to read and write every byte of the file. Therefore, the time complexity of the code is O(n), where n is the size of the source_file.

Space Complexity:
The space complexity of the code is O(1), as it does not allocate any additional memory beyond what is required for the file objects source_file and f. The shutil.copyfileobj() function copies the file contents in chunks, so it does not need to load the entire file into memory at once.

Overall, the code has a linear time complexity and constant space complexity, where the time complexity is proportional to the size of the file being copied.

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