Practice: Merge Two Files

Lesson

Practice: Merge Two Files

This exercise combines reading and writing in one function.

Exercise

Define a function named merge_files with three parameters: first_path, second_path, and output_path.
It writes the full content of the first file, then the full content of the second, into the output file — replacing whatever the output file held.

If a.txt contains one and a newline, and b.txt contains two and a newline, the output file contains one, newline, two, newline.

Run your code to see the output, then press Submit.

Hints

Read both inputs into strings, then open the output with "w" and write both.
No line processing needed — read and write the whole contents.

Tests

import unittest


class TestMergeFiles(unittest.TestCase):
    def setUp(self):
        with open("test_a.txt", "w") as file:
            file.write("one\n")
        with open("test_b.txt", "w") as file:
            file.write("two\n")

    def test_output_holds_both_in_order(self):
        merge_files("test_a.txt", "test_b.txt", "test_out.txt")
        with open("test_out.txt") as file:
            self.assertEqual(file.read(), "one\ntwo\n")

    def test_existing_output_is_replaced(self):
        with open("test_out.txt", "w") as file:
            file.write("stale\n")
        merge_files("test_a.txt", "test_b.txt", "test_out.txt")
        with open("test_out.txt") as file:
            self.assertEqual(file.read(), "one\ntwo\n")

    def test_inputs_are_unchanged(self):
        merge_files("test_a.txt", "test_b.txt", "test_out.txt")
        with open("test_a.txt") as file:
            self.assertEqual(file.read(), "one\n")

Solution

def merge_files(first_path, second_path, output_path):
    with open(first_path) as file:
        first_content = file.read()
    with open(second_path) as file:
        second_content = file.read()
    with open(output_path, "w") as file:
        file.write(first_content)
        file.write(second_content)


with open("a.txt", "w") as file:
    file.write("one\n")
with open("b.txt", "w") as file:
    file.write("two\n")

merge_files("a.txt", "b.txt", "merged.txt")
with open("merged.txt") as file:
    print(file.read())

Solution hidden. Give it a real try first.

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main.py

Console

Press Run to execute your code, or Submit to test and complete this problem.