Write Lines

Zero-dependency Python snippets for writing lines to files using the standard library.

4 snippets available in this sub-category.

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Simple

Write list of lines to file

file write lines list writelines

Write a list of strings to file without newlines

lines = ["Line 1", "Line 2", "Line 3"]
with open("file.txt", "w") as f:
    f.writelines(lines)

Notes

• Writes strings without adding newlines
• Overwrites existing file
• Each string becomes one line

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Write lines with newlines

file write lines newline loop

Write lines to file with explicit newlines

lines = ["Line 1", "Line 2", "Line 3"]
with open("file.txt", "w") as f:
    for line in lines:
        f.write(line + "\n")

Notes

• Adds newline after each line
• More explicit than writelines()
• Easy to customize line endings

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Complex

Write lines with numbering

file write lines enumerate

Write lines to file with automatic line numbering

def write_lines_with_numbers(filename, lines, start_number=1):
    """Write lines to file with line numbers."""
    with open(filename, "w") as f:
        for i, line in enumerate(lines, start_number):
            f.write(f"{i:3d}: {line}\n")


lines = ["First line", "Second line", "Third line"]
write_lines_with_numbers("numbered.txt", lines)

Notes

• Adds line numbers to each line
• Configurable starting number
• Right-aligned line numbers
• Useful for debugging and logs

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Write lines with filtering

file write lines filter lambda custom

Write lines to file with custom filtering function

def write_lines_filtered(filename, lines, filter_func=None):
    """Write lines to file with optional filtering."""
    with open(filename, "w") as f:
        for line in lines:
            if filter_func is None or filter_func(line):
                f.write(line + "\n")


lines = ["Line 1", "", "Line 3", "  ", "Line 5"]

# Write only non-empty lines
write_lines_filtered("filtered.txt", lines, lambda x: x.strip())

# Write only lines starting with 'Line'
write_lines_filtered("filtered2.txt", lines, lambda x: x.startswith("Line"))

Notes

• Applies filter function to each line
• Skips lines that don't pass filter
• Flexible filtering criteria
• Useful for data cleaning

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🔗 Cross-References

• Reference: See 📂 Write File
• Reference: See 📂 Read File Lines

🏷️ Tags

file, write, lines, text, io

📝 Notes

• Use writelines() to write multiple lines to a file
• Add newlines manually if needed
• Useful for logs, reports, and batch output