Difflib - Understanding difflib.Differ in Python

The `difflib` module in Python provides a powerful tool for comparing sequences of lines and generating human-readable differences or deltas. Within this module, the `Differ` class stands out as a key component for comparing text-based data. In this article, we'll explore the functionality of `difflib.Differ` and how it aids in highlighting differences between sequences.

Key Concepts

Comparison Codes: The Differ class utilizes a set of two-letter codes to signify the meaning of each line in the delta. These codes include the following.

'- ': Line unique to sequence 1.

'+ ': Line unique to sequence 2.

'  ': Line common to both sequences.

'? ': Line not present in either input sequence.

Intraline Differences: Lines starting with '?' are designed to draw attention to intraline differences, providing insight into character-level variations within similar lines.

Handling Whitespace: Caution is advised when dealing with sequences containing whitespace characters (e.g., spaces, tabs, line breaks), as these may affect the interpretation of differences.

Example Usage

	import difflib
	before_code = '''
	#include <stdio.h>
	int main() {
	int num1, num2;
	char operator;
	printf("Enter first number: ");
	scanf("%d", &num1);
	printf("Enter operator (+, -, *, /): ");
	scanf(" %c", &operator);
	printf("Enter second number: ");
	scanf("%d", &num2);
	switch (operator) {
	case '+':
	printf("Result: %d\n", num1 + num2);
	break;
	case '-':
	printf("Result: %d\n", num1 - num2);
	break;
	case '*':
	printf("Result: %d\n", num1 * num2);
	break;
	case '/':
	if (num2 != 0) {
	printf("Result: %.2f\n", (float)num1 / num2);
	} else {
	printf("Error: Division by zero is not allowed.\n");
	}
	break;
	default:
	printf("Error: Invalid operator.\n");
	break;
	}
	return 0;
	}
	'''
	after_code = '''
	#include <stdio.h>
	int main() {
	int num1, num2;
	char operator;
	// Validate user input
	if (scanf("%d %c %d", &num1, &operator, &num2) != 3) {
	printf("Invalid input. Please try again.\n");
	return 1;
	}
	// Check for valid operator
	if (operator != '+' && operator != '-' && operator != '*' && operator != '/') {
	printf("Invalid operator. Please try again.\n");
	return 1;
	}
	// Check for division by zero
	if (operator == '/' && num2 == 0) {
	printf("Error: Division by zero is not allowed.\n");
	return 1;
	}
	// Perform calculation
	int result;
	switch (operator) {
	case '+':
	result = num1 + num2;
	break;
	case '-':
	result = num1 - num2;
	break;
	case '*':
	result = num1 * num2;
	break;
	case '/':
	result = num1 / num2;
	break;
	default:
	printf("Invalid operator. Please try again.\n");
	return 1;
	}
	// Output result
	printf("Result: %d\n", result);
	return 0;
	}
	'''
	# Split the code into lines
	before_lines = before_code.splitlines()
	after_lines = after_code.splitlines()
	# Perform the difference analysis
	differ = difflib.Differ()
	diff = list(differ.compare(before_lines, after_lines))
	# Extract the changed blocks
	changed_blocks = []
	current_block = []
	for line in diff:
	if line.startswith(' '):
	if current_block:
	changed_blocks.append(current_block)
	current_block = []
	else:
	current_block.append(line)
	# Add the last block if any
	if current_block:
	changed_blocks.append(current_block)
	# Display the changed blocks
	for block in changed_blocks:
	print("\n".join(block))
	print("***************")

view raw main.py hosted with ❤ by GitHub

Understanding how to use `difflib.Differ` empowers Python developers to efficiently compare and analyze textual data, identify discrepancies between sequences, and ultimately enhance the clarity of differences in their applications.