How can I efficiently insert a line at a specific position in a text file using Python?

Modifying Files Efficiently: Inserting Lines with Python

Often, we need to modify existing text files, such as inserting new lines or correcting errors. One such task is to insert a line at a specific position in a file. With Python, this operation can be executed efficiently.

Problem Statement

Consider a text file containing a list of names in sequential order, as shown below:

Alfred
Bill
Donald

Our objective is to insert a third name, "Charlie," at line 3 of this file. The subsequent lines should automatically shift down one line to accommodate the new entry.

Solution

Using Python's file handling capabilities, we can insert a line at a specified location. The code snippet below demonstrates this technique:

<code class="python">with open("path_to_file", "r") as f:
    contents = f.readlines()

contents.insert(2, "Charlie\n")

with open("path_to_file", "w") as f:
    contents = "".join(contents)
    f.write(contents)</code>

In this code:

• The file is opened in read mode ('r').
• The readlines() method is used to read the entire file into a list called contents.
• The insert() method inserts "Charlie" into line 3 of the contents list (index 2, since lines start from 0).
• The list is then converted back into a string using "".join(...) and written to the file in write mode ('w').
• The file is reopened in write mode to truncate it and write the modified content.

Conclusion

This approach allows for efficient line insertion in text files, making it a useful technique for various file manipulation tasks.

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