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

The `mimetypes` module 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 latter conversion.

The module provides one class and a number of convenience functions. The functions are the normal interface to this module, but some applications may be interested in the class as well.

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

`guess_type`( | filename[, strict])

  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 (missing or unknown suffix) or a string of the form `'type/subtype'`, usable for a MIME content-type: header.

  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 sensitively, then case insensitively.

  Optional strict is a flag specifying whether the list of known MIME types is limited to only the official types registered with IANA are recognized. When strict is true (the default), only the IANA types are supported; when strict is false, some additional non-standard but commonly used MIME types are also recognized.

`guess_all_extensions`( | type[, strict])

  Guess the extensions for a file based on its MIME type, given by type. The return value is a list of strings giving all possible filename extensions, including the leading dot ("`.`"). The extensions are not guaranteed to have been associated with any particular data stream, but would be mapped to the MIME type type by `guess_type()`.

  Optional strict has the same meaning as with the `guess_type()` function.

`guess_extension`( | type[, strict])

  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.

  Optional strict has the same meaning as with the `guess_type()` function.

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.

`add_type`( | type, ext[, strict])

  Add a mapping from the mimetype type to the extension ext. When the extension is already known, the new type will replace the old one. When the type is already known the extension will be added to the list of known extensions.

  When strict is the mapping will added to the official MIME types, otherwise to the non-standard ones.

`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.

`common_types`
  Dictionary mapping filename extensions to non-standard, but commonly found MIME types.

The `MimeTypes` class may be useful for applications which may want more than one MIME-type database:

class `MimeTypes`( | [filenames])

  This class represents a MIME-types database. By default, it provides access to the same database as the rest of this module. The initial database is a copy of that provided by the module, and may be extended by loading additional mime.types-style files into the database using the `read()` or `readfp()` methods. The mapping dictionaries may also be cleared before loading additional data if the default data is not desired.

  The optional filenames parameter can be used to cause additional files to be loaded ``on top'' of the default database.

  New in version 2.2.