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Determines the MIME type of a file based on its file extension by mapping common extensions to their corresponding MIME type strings.

Purpose

This function provides a simple file extension to MIME type mapping for common document and image formats. It's useful for setting proper Content-Type headers when serving files, validating file uploads, or preparing files for transmission. The function returns a default MIME type ('application/octet-stream') for unknown extensions, making it safe to use with any filename.

Source Code

def get_mime_type(filename: str) -> str:
    """
    Get MIME type for a file based on extension.
    
    Args:
        filename: Filename
        
    Returns:
        MIME type string
    """
    ext = get_file_extension(filename)
    mime_types = {
        "pdf": "application/pdf",
        "doc": "application/msword",
        "docx": "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
        "txt": "text/plain",
        "rtf": "application/rtf",
        "jpg": "image/jpeg",
        "jpeg": "image/jpeg",
        "png": "image/png",
        "gif": "image/gif"
    }
    return mime_types.get(ext, "application/octet-stream")

Parameters

Parameter Details

filename: A string representing the filename (with or without path). The function extracts the file extension from this string to determine the MIME type. Can be a full path like '/path/to/file.pdf' or just a filename like 'document.pdf'. Case handling depends on the get_file_extension function implementation.

Return Value

Type: str

Returns a string representing the MIME type of the file. For recognized extensions (pdf, doc, docx, txt, rtf, jpg, jpeg, png, gif), returns the appropriate MIME type (e.g., 'application/pdf', 'image/jpeg'). For unrecognized extensions, returns 'application/octet-stream' as a safe default for binary data.

Usage Example

# Assuming get_file_extension is defined elsewhere in the module
def get_file_extension(filename: str) -> str:
    return filename.rsplit('.', 1)[-1].lower() if '.' in filename else ''

# Example usage
mime_type = get_mime_type('document.pdf')
print(mime_type)  # Output: 'application/pdf'

mime_type = get_mime_type('/path/to/image.jpg')
print(mime_type)  # Output: 'image/jpeg'

mime_type = get_mime_type('spreadsheet.xlsx')
print(mime_type)  # Output: 'application/octet-stream' (unknown extension)

mime_type = get_mime_type('report.docx')
print(mime_type)  # Output: 'application/vnd.openxmlformats-officedocument.wordprocessingml.document'

Best Practices

• This function depends on get_file_extension being available in scope - ensure it's defined or imported before using get_mime_type
• The function only supports a limited set of file extensions - consider extending the mime_types dictionary for additional file types if needed
• Returns 'application/octet-stream' as a safe default for unknown extensions, which is appropriate for binary data but may need customization for specific use cases
• For production use, consider using Python's built-in mimetypes module (import mimetypes; mimetypes.guess_type()) which provides more comprehensive coverage
• The function assumes get_file_extension returns lowercase extensions - verify this behavior for case-sensitive scenarios
• Does not validate if the file actually exists or if its content matches the extension - this is purely extension-based detection

Tags

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