LexicalInferencer¶

Fastest inferencer that extracts file extensions directly from file paths.

from filetype_detector import LexicalInferencer

Overview¶

The LexicalInferencer is the fastest file type detection method, extracting file extensions directly from file paths without reading file contents. This makes it ideal for scenarios where file extensions are trusted or when maximum performance is required.

Class Definition¶

class LexicalInferencer(BaseInferencer):
    """Lexical inferencer that uses the file path to infer the file format."""

Methods¶

`infer(file_path: Union[Path, str]) -> FileType`¶

Infer the file format from the file path.

Parameters:

file_path (Union[Path, str]): Path to the file. Can be a Path object or a string representing the file system path.

Returns:

FileType: A frozen dataclass with extensions and mime_types tuples. Raises ValueError if the path has no extension.

Examples:

from filetype_detector import LexicalInferencer
from pathlib import Path

inferencer = LexicalInferencer()

# String path
ft = inferencer.infer('document.pdf')
'.pdf' in ft.extensions  # True

# Path object
ft = inferencer.infer(Path('data.txt'))
'.txt' in ft.extensions  # True

# No extension
inferencer.infer('no_extension')  # Raises ValueError

Usage Examples¶

Basic Usage¶

from filetype_detector import LexicalInferencer

inferencer = LexicalInferencer()
ft = inferencer.infer("document.pdf")
'.pdf' in ft.extensions  # True
ft.mime_types             # ('application/pdf',)

Case Insensitive¶

The inferencer automatically converts extensions to lowercase:

inferencer = LexicalInferencer()
ft1 = inferencer.infer("FILE.PDF")
ft2 = inferencer.infer("file.pdf")
'.pdf' in ft1.extensions  # True
'.pdf' in ft2.extensions  # True

Multiple Dots¶

When filenames contain multiple dots, returns the last extension:

inferencer = LexicalInferencer()
ft1 = inferencer.infer("file.tar.gz")
'.gz' in ft1.extensions   # True

Files Without Extensions¶

Paths without a suffix are invalid lexical inputs:

inferencer = LexicalInferencer()

try:
    inferencer.infer("no_extension")
except ValueError:
    print("No extension detected")

try:
    inferencer.infer(".hidden")
except ValueError:
    print("No extension detected")

Performance¶

Speed: Fastest (~< 0.001ms per file)
I/O: None (pure string manipulation)
Memory: Minimal
Throughput: 50,000+ files/second

When to Use¶

✅ Good for: - High-volume processing where extensions are trusted - Maximum performance requirements - Simple extension extraction without content analysis - Cases where file I/O should be avoided

❌ Not suitable for: - Detecting incorrect file extensions - Files without extensions - Content-based type detection - Validating file types

Limitations¶

Cannot detect wrong extensions: A file named document.pdf will return a FileType with .pdf even if it's actually a Word document
Missing extension error: Paths without extensions raise ValueError
No content analysis: Pure path-based detection only

Error Handling¶

LexicalInferencer does not access the filesystem. It accepts path-like strings whether or not the file exists, but raises ValueError when the path has no extension.

inferencer = LexicalInferencer()

try:
    file_type = inferencer.infer("file_without_ext")
except ValueError as error:
    print(error)
else:
    print(file_type.extensions)