How to Update Parts of a Plain Text Configuration File in Python

What will you learn?

In this comprehensive tutorial, you will master the art of updating specific sections of a plain text configuration file using Python. By the end of this guide, you will possess a powerful skill set to efficiently search for and replace parts of text within configuration files while preserving the original file structure.

Introduction to Problem and Solution

Managing application configurations or system settings often involves dealing with plain text files. While these files are human-readable and easily modifiable, manually updating them can be error-prone, especially when handling extensive configurations or automating tasks.

To address this challenge, we leverage Python’s robust capabilities to read the file content into memory, identify the sections or keys that require modification, update their values as needed, and finally write back the modified content to the file. This approach ensures a simple yet effective way to handle string manipulation and file operations efficiently.


def update_config(file_path, changes):
    # Read the existing configuration from file
    with open(file_path, 'r') as file:
        config_lines = file.readlines()

    # Apply changes specified in `changes` dict
    updated_lines = []
    for line in config_lines:
        for key, new_value in changes.items():
            if line.startswith(key):
                line = f"{key}={new_value}\n"
                break  # Stop looking for other keys in this line

    # Write updated configuration back to file
    with open(file_path, 'w') as file:
        for line in updated_lines:

# Example usage:
config_changes = {"setting1": "newValue1", "setting2": "newValue2"}
update_config("path/to/config.file", config_changes)

# Copyright PHD


The update_config function takes two parameters: file_path, indicating the location of your configuration file; and changes, a dictionary where each key-value pair represents a setting name and its corresponding new value. The process unfolds step-by-step:

  • Reading: Open the original config file in read mode (‘r’) and read all lines into memory.
  • Updating: Iterate through each line of the config data. For every line,
    • Check against each key from the changes dictionary.
    • If a key matches at the beginning of a line (indicating it’s a setting), replace that entire line with one containing the new value.
    • This method ensures only specified settings are altered while preserving other content such as comments or empty lines.
  • Writing: Open the file again in write mode (‘w’) and rewrite all lines (potentially modified) back into the same path, effectively updating it.

This technique is most effective for simple assignment-based configurations like KEY=VALUE pairs. For more complex scenarios involving nested structures or different formats such as JSON/YAML/XML files, consider utilizing libraries tailored for those formats.

  1. How do I add new settings not already present?

  2. If you need to add entirely new settings that do not exist yet while updating existing keys, after checking all lines during updates append these additional settings either at the beginning or end based on your preference before writing back.

  3. Can I comment out an existing setting instead of removing it?

  4. Certainly! Adjust your condition within the loop so instead of replacing entirely, you can create something like “#” +line, effectively commenting out the designated setting while keeping everything else intact.

  5. Does this work with JSON/YAML/XML files?

  6. The provided script focuses on plain-text KEY=VALUE pairs commonly found in .ini or similar styled configs. For structured data formats like JSON/YAML/XML, specialized parsers offer better support for handling complexities inherent within those types.

  7. What about concurrent modifications?

  8. When multiple processes attempt to alter the same piece simultaneously, there are risks of corruption. Implement mechanisms like locking to ensure single access at a time safeguarding integrity during writes.

  9. Can I use regular expressions for more complex replacements?

  10. Absolutely! The standard library´┐Żs re module allows pattern matching offering greater precision/control over modifications fitting diverse needs beyond straightforward substring matches/replacements.


Mastering how to manipulate plain text configuration files using Python equips you with invaluable skills essential for automating scripting tasks and simplifying system/application maintenance. By considering potential edge cases outlined in FAQs, you ensure smooth operation while avoiding unintended consequences.

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