How to check file data in Python

Check if a file exists and is a regular file, then return its name, size, line count, and first line.

Easy Python 3.9+ Aug 9, 2026 Files & data 15 views 0 copies

file pathlib metadata check

Python code

28 lines

Python 3.9+

def check_file_data(file_path):
    from pathlib import Path
    path = Path(file_path)
    if not path.exists():
        return f"File '{file_path}' does not exist."
    if not path.is_file():
        return f"'{file_path}' is not a regular file."
    
    size = path.stat().st_size
    lines = path.read_text(encoding='utf-8', errors='replace').splitlines()
    
    return {
        "exists": True,
        "name": path.name,
        "size_bytes": size,
        "line_count": len(lines),
        "first_line": lines[0] if lines else "",
    }


if __name__ == "__main__":
    import tempfile, os
    with tempfile.NamedTemporaryFile(mode='w', delete=False, suffix='.txt') as f:
        f.write("hello\nworld\n")
        temp_path = f.name
    result = check_file_data(temp_path)
    print(result)
    os.unlink(temp_path)

Output

stdout

{'exists': True, 'name': 'tmpXXXX.txt', 'size_bytes': 12, 'line_count': 2, 'first_line': 'hello'}

How it works

The path.exists() check prevents errors when the file is missing, and path.is_file() ensures it's not a directory. path.stat().st_size gives the byte size. Reading with read_text and splitlines() counts lines after stripping newline characters. The errors='replace' handles non-UTF-8 characters gracefully.

Common mistakes

Using `os.path.exists` and forgetting to check if it's a file, not a directory
Reading binary files as text without handling encoding errors
Assuming the file is non-empty and indexing `lines[0]` without checking length

Variations

Use `os.stat(file_path).st_size` and `open(file_path).readlines()` for a simpler version
Return `None` or raise a custom exception instead of returning error strings

Real-world use cases

Checking if a config file is present and non-empty before parsing it at app startup.
Validating that an upload is a real file, not a directory, and reporting its size and size.
Preparing a file summary for logging or monitoring, including line count and first line.

How to check file data in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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