Writing to Files

Use write mode and append mode to save data to files

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Write mode vs append mode

Open a file in "w" mode to write new content. If the file already exists, Python overwrites it completely.

with open("output.txt", "w") as file:
    file.write("Hello, world!\n")

Open a file in "a" mode to add content to the end without deleting what is already there.

with open("output.txt", "a") as file:
    file.write("Another line.\n")

The `.write()` method

.write() writes a string to the file. It does not add a newline automatically — you must include \n at the end of each line.

file.write("Line 1\n")
file.write("Line 2\n")

Confirming a write

Since writing does not produce visible output, always print() a confirmation message so you know the operation succeeded.

Instructions

Write two lines to a file, then append a third line.

Open notes.txt in write mode using with open("notes.txt", "w") as file:. Inside the block, call file.write("Line 1: Python is fun\n"), then call file.write("Line 2: Files are useful\n").
After the block, call print("notes.txt created.").
Open notes.txt in append mode using with open("notes.txt", "a") as file:. Inside the block, call file.write("Line 3: Appended line\n").
After the block, call print("notes.txt updated.").

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# Step 1: Open notes.txt in write mode and write both lines inside the block

# Step 2: Print "notes.txt created."

# Step 3: Open notes.txt in append mode and write the third line inside the block

# Step 4: Print "notes.txt updated."

Writing to Files

Write mode vs append mode

The .write() method

Confirming a write

Instructions

Interactive Code Editor

The `.write()` method