# 12.15 `mimetypes` -- Map filenames to MIME types

The `mimetypes` converts between a filename or URL and the MIME type associated with the filename extension. Conversions are provided from filename to MIME type and from MIME type to filename extension; encodings are not supported for the later conversion.

The functions described below provide the primary interface for this module. If the module has not been initialized, they will call `init()`.

`guess_type` (filename)
  Guess the type of a file based on its filename or URL, given by filename. The return value is a tuple `(type, encoding)` where type is `None` if the type can't be guessed (no or unknown suffix) or a string of the form `'type/subtype'`, usable for a MIME `content-type` header; and encoding is `None` for no encoding or the name of the program used to encode (e.g. compress or gzip). The encoding is suitable for use as a `content-encoding` header, not as a `content-transfer-encoding` header. The mappings are table driven. Encoding suffixes are case sensitive; type suffixes are first tried case sensitive, then case insensitive.

`guess_extension` (type)
  Guess the extension for a file based on its MIME type, given by type. The return value is a string giving a filename extension, including the leading dot ("`.`"). The extension is not guaranteed to have been associated with any particular data stream, but would be mapped to the MIME type type by `guess_type()`. If no extension can be guessed for type, `None` is returned.

Some additional functions and data items are available for controlling the behavior of the module.

`init` ([files])
  Initialize the internal data structures. If given, files must be a sequence of file names which should be used to augment the default type map. If omitted, the file names to use are taken from `knownfiles`. Each file named in files or `knownfiles` takes precedence over those named before it. Calling `init()` repeatedly is allowed.

`read_mime_types` (filename)
  Load the type map given in the file filename, if it exists. The type map is returned as a dictionary mapping filename extensions, including the leading dot ("`.`"), to strings of the form `'type/subtype'`. If the file filename does not exist or cannot be read, `None` is returned.

`inited`
  Flag indicating whether or not the global data structures have been initialized. This is set to true by `init()`.

`knownfiles`
  List of type map file names commonly installed. These files are typically named mime.types and are installed in different locations by different packages.

`suffix_map`
  Dictionary mapping suffixes to suffixes. This is used to allow recognition of encoded files for which the encoding and the type are indicated by the same extension. For example, the .tgz extension is mapped to .tar.gz to allow the encoding and type to be recognized separately.

`encodings_map`
  Dictionary mapping filename extensions to encoding types.

`types_map`
  Dictionary mapping filename extensions to MIME types.