# Sanitizing text fragments

`bleach.clean()` is Bleach’s HTML sanitization method.

Given a fragment of HTML, Bleach will parse it according to the HTML5 parsing algorithm and sanitize any disallowed tags or attributes. This algorithm also takes care of things like unclosed and (some) misnested tags.

You may pass in a `string` or a `unicode` object, but Bleach will always return `unicode`.

Note

`bleach.clean()` is for sanitizing HTML fragments and not entire HTML documents.

Warning

`bleach.clean()` is for sanitising HTML fragments to use in an HTML context–not for HTML attributes, CSS, JSON, xhtml, SVG, or other contexts.

For example, this is a safe use of `clean` output in an HTML context:

    <p>
      {{ bleach.clean(user_bio) }}
    </p>

This is a not safe use of `clean` output in an HTML attribute:

    <body data-bio="{{ bleach.clean(user_bio} }}">

If you need to use the output of `bleach.clean()` in an HTML attribute, you need to pass it through your template library’s escape function. For example, Jinja2’s `escape` or `django.utils.html.escape` or something like that.

If you need to use the output of `bleach.clean()` in any other context, you need to pass it through an appropriate sanitizer/escaper for that context.

`bleach.``clean`(text, tags=['a', 'abbr', 'acronym', 'b', 'blockquote', 'code', 'em', 'i', 'li', 'ol', 'strong', 'ul'], attributes={'a': ['href', 'title'], 'abbr': ['title'], 'acronym': ['title']}, styles=[], protocols=['http', 'https', 'mailto'], strip=False, strip_comments=True)

  Clean an HTML fragment of malicious content and return it

  This function is a security-focused function whose sole purpose is to remove malicious content from a string such that it can be displayed as content in a web page.

  This function is not designed to use to transform content to be used in non-web-page contexts.

  Example:

      import bleach

      better_text = bleach.clean(yucky_text)

  Note

  If you’re cleaning a lot of text and passing the same argument values or you want more configurability, consider using a `bleach.sanitizer.Cleaner` instance.

  Parameters:

  - text (str) – the text to clean
  - tags (list) – allowed list of tags; defaults to `bleach.sanitizer.ALLOWED_TAGS`
  - attributes (dict) – allowed attributes; can be a callable, list or dict; defaults to `bleach.sanitizer.ALLOWED_ATTRIBUTES`
  - styles (list) – allowed list of css styles; defaults to `bleach.sanitizer.ALLOWED_STYLES`
  - protocols (list) – allowed list of protocols for links; defaults to `bleach.sanitizer.ALLOWED_PROTOCOLS`
  - strip (bool) – whether or not to strip disallowed elements
  - strip_comments (bool) – whether or not to strip HTML comments

  Returns: | cleaned text as unicode

## Allowed tags (`tags`)

The `tags` kwarg specifies the allowed set of HTML tags. It should be a list, tuple, or other iterable. Any HTML tags not in this list will be escaped or stripped from the text.

For example:

    >>> import bleach

    >>> bleach.clean(
    ...     '<b><i>an example</i></b>',
    ...     tags=['b'],
    ... )
    '<b>&lt;i&gt;an example&lt;/i&gt;</b>'

The default value is a relatively conservative list found in `bleach.sanitizer.ALLOWED_TAGS`.

`bleach.sanitizer.``ALLOWED_TAGS` = ['a', 'abbr', 'acronym', 'b', 'blockquote', 'code', 'em', 'i', 'li', 'ol', 'strong', 'ul']

  List of allowed tags

## Allowed Attributes (`attributes`)

The `attributes` kwarg lets you specify which attributes are allowed. The value can be a list, a callable or a map of tag name to list or callable.

The default value is also a conservative dict found in `bleach.sanitizer.ALLOWED_ATTRIBUTES`.

`bleach.sanitizer.``ALLOWED_ATTRIBUTES` = {'a': ['href', 'title'], 'abbr': ['title'], 'acronym': ['title']}

  Map of allowed attributes by tag

Changed in version 2.0: Prior to 2.0, the `attributes` kwarg value could only be a list or a map.

### As a list

The `attributes` value can be a list which specifies the list of attributes allowed for any tag.

For example:

    >>> import bleach

    >>> bleach.clean(
    ...     '<p class="foo" style="color: red; font-weight: bold;">blah blah blah</p>',
    ...     tags=['p'],
    ...     attributes=['style'],
    ...     styles=['color'],
    ... )
    '<p style="color: red;">blah blah blah</p>'

### As a dict

The `attributes` value can be a dict which maps tags to what attributes they can have.

You can also specify `*`, which will match any tag.

For example, this allows “href” and “rel” for “a” tags, “alt” for the “img” tag and “class” for any tag (including “a” and “img”):

    >>> import bleach

    >>> attrs = {
    ...     '*': ['class'],
    ...     'a': ['href', 'rel'],
    ...     'img': ['alt'],
    ... }

    >>> bleach.clean(
    ...    '<img alt="an example" width=500>',
    ...    tags=['img'],
    ...    attributes=attrs
    ... )
    '<img alt="an example">'

### Using functions

You can also use callables that take the tag, attribute name and attribute value and returns `True` to keep the attribute or `False` to drop it.

You can pass a callable as the attributes argument value and it’ll run for every tag/attr.

For example:

    >>> import bleach

    >>> def allow_h(tag, name, value):
    ...     return name[0] == 'h'

    >>> bleach.clean(
    ...    '<a href="http://example.com" title="link">link</a>',
    ...    tags=['a'],
    ...    attributes=allow_h,
    ... )
    '<a href="http://example.com">link</a>'

You can also pass a callable as a value in an attributes dict and it’ll run for attributes for specified tags:

    >>> from six.moves.urllib.parse import urlparse
    >>> import bleach

    >>> def allow_src(tag, name, value):
    ...     if name in ('alt', 'height', 'width'):
    ...         return True
    ...     if name == 'src':
    ...         p = urlparse(value)
    ...         return (not p.netloc) or p.netloc == 'mydomain.com'
    ...     return False

    >>> bleach.clean(
    ...    '<img src="http://example.com" alt="an example">',
    ...    tags=['img'],
    ...    attributes={
    ...        'img': allow_src
    ...    }
    ... )
    '<img alt="an example">'

Changed in version 2.0: In previous versions of Bleach, the callable took an attribute name and a attribute value. Now it takes a tag, an attribute name and an attribute value.

## Allowed styles (`styles`)

If you allow the `style` attribute, you will also need to specify the allowed styles users are allowed to set, for example `color` and `background-color`.

The default value is an empty list. In other words, the `style` attribute will be allowed but no style declaration names will be allowed.

For example, to allow users to set the color and font-weight of text:

    >>> import bleach

    >>> tags = ['p', 'em', 'strong']
    >>> attrs = {
    ...     '*': ['style']
    ... }
    >>> styles = ['color', 'font-weight']

    >>> bleach.clean(
    ...     '<p style="font-weight: heavy;">my html</p>',
    ...     tags=tags,
    ...     attributes=attrs,
    ...     styles=styles
    ... )
    '<p style="font-weight: heavy;">my html</p>'

Default styles are stored in `bleach.sanitizer.ALLOWED_STYLES`.

`bleach.sanitizer.``ALLOWED_STYLES` = []

  List of allowed styles

## Allowed protocols (`protocols`)

If you allow tags that have attributes containing a URI value (like the `href` attribute of an anchor tag, you may want to adapt the accepted protocols.

For example, this sets allowed protocols to http, https and smb:

    >>> import bleach

    >>> bleach.clean(
    ...     '<a href="smb://more_text">allowed protocol</a>',
    ...     protocols=['http', 'https', 'smb']
    ... )
    '<a href="smb://more_text">allowed protocol</a>'

This adds smb to the Bleach-specified set of allowed protocols:

    >>> import bleach

    >>> bleach.clean(
    ...     '<a href="smb://more_text">allowed protocol</a>',
    ...     protocols=bleach.ALLOWED_PROTOCOLS + ['smb']
    ... )
    '<a href="smb://more_text">allowed protocol</a>'

Default protocols are in `bleach.sanitizer.ALLOWED_PROTOCOLS`.

`bleach.sanitizer.``ALLOWED_PROTOCOLS` = ['http', 'https', 'mailto']

  List of allowed protocols

## Stripping markup (`strip`)

By default, Bleach escapes tags that aren’t specified in the allowed tags list and invalid markup. For example:

    >>> import bleach

    >>> bleach.clean('<span>is not allowed</span>')
    '&lt;span&gt;is not allowed&lt;/span&gt;'

    >>> bleach.clean('<b><span>is not allowed</span></b>', tags=['b'])
    '<b>&lt;span&gt;is not allowed&lt;/span&gt;</b>'

If you would rather Bleach stripped this markup entirely, you can pass `strip=True`:

    >>> import bleach

    >>> bleach.clean('<span>is not allowed</span>', strip=True)
    'is not allowed'

    >>> bleach.clean('<b><span>is not allowed</span></b>', tags=['b'], strip=True)
    '<b>is not allowed</b>'

## Stripping comments (`strip_comments`)

By default, Bleach will strip out HTML comments. To disable this behavior, set `strip_comments=False`:

    >>> import bleach

    >>> html = 'my<!-- commented --> html'

    >>> bleach.clean(html)
    'my html'

    >>> bleach.clean(html, strip_comments=False)
    'my<!-- commented --> html'

## Using `bleach.sanitizer.Cleaner`

If you’re cleaning a lot of text or you need better control of things, you should create a `bleach.sanitizer.Cleaner` instance.

class `bleach.sanitizer.``Cleaner`(tags=['a', 'abbr', 'acronym', 'b', 'blockquote', 'code', 'em', 'i', 'li', 'ol', 'strong', 'ul'], attributes={'a': ['href', 'title'], 'abbr': ['title'], 'acronym': ['title']}, styles=[], protocols=['http', 'https', 'mailto'], strip=False, strip_comments=True, filters=None)

  Cleaner for cleaning HTML fragments of malicious content

  This cleaner is a security-focused function whose sole purpose is to remove malicious content from a string such that it can be displayed as content in a web page.

  To use:

      from bleach.sanitizer import Cleaner

      cleaner = Cleaner()

      for text in all_the_yucky_things:
          sanitized = cleaner.clean(text)

  Note

  This cleaner is not designed to use to transform content to be used in non-web-page contexts.

  Warning

  This cleaner is not thread-safe–the html parser has internal state. Create a separate cleaner per thread!

  Initializes a Cleaner

  Parameters:

  - tags (list) – allowed list of tags; defaults to `bleach.sanitizer.ALLOWED_TAGS`
  - attributes (dict) – allowed attributes; can be a callable, list or dict; defaults to `bleach.sanitizer.ALLOWED_ATTRIBUTES`
  - styles (list) – allowed list of css styles; defaults to `bleach.sanitizer.ALLOWED_STYLES`
  - protocols (list) – allowed list of protocols for links; defaults to `bleach.sanitizer.ALLOWED_PROTOCOLS`
  - strip (bool) – whether or not to strip disallowed elements
  - strip_comments (bool) – whether or not to strip HTML comments
  - filters (list) –

    list of html5lib Filter classes to pass streamed content through

    See also

    http://html5lib.readthedocs.io/en/latest/movingparts.html#filters

    Warning

    Using filters changes the output of `bleach.Cleaner.clean`. Make sure the way the filters change the output are secure.

  `clean`(text)

    Cleans text and returns sanitized result as unicode

    Parameters: | text (str) – text to be cleaned
    Returns: | sanitized text as unicode
    Raises: | TypeError – if `text` is not a text type

New in version 2.0.

### html5lib Filters (`filters`)

Bleach sanitizing is implemented as an html5lib filter. The consequence of this is that we can pass the streamed content through additional specified filters after the `bleach.sanitizer.BleachSanitizingFilter` filter has run.

This lets you add data, drop data and change data as it is being serialized back to a unicode.

Documentation on html5lib Filters is here: http://html5lib.readthedocs.io/en/latest/movingparts.html#filters

Trivial Filter example:

    >>> from bleach.sanitizer import Cleaner
    >>> from bleach.html5lib_shim import Filter

    >>> class MooFilter(Filter):
    ...     def __iter__(self):
    ...         for token in Filter.__iter__(self):
    ...             if token['type'] in ['StartTag', 'EmptyTag'] and token['data']:
    ...                 for attr, value in token['data'].items():
    ...                     token['data'][attr] = 'moo'
    ...             yield token
    ...
    >>> ATTRS = {
    ...     'img': ['rel', 'src']
    ... }
    ...
    >>> TAGS = ['img']
    >>> cleaner = Cleaner(tags=TAGS, attributes=ATTRS, filters=[MooFilter])
    >>> dirty = 'this is cute! <img src="http://example.com/puppy.jpg" rel="nofollow">'
    >>> cleaner.clean(dirty)
    'this is cute! <img rel="moo" src="moo">'

Warning

Filters change the output of cleaning. Make sure that whatever changes the filter is applying maintain the safety guarantees of the output.

New in version 2.0.

## Using `bleach.sanitizer.BleachSanitizerFilter`

`bleach.clean` creates a `bleach.sanitizer.Cleaner` which creates a `bleach.sanitizer.BleachSanitizerFilter` which does the sanitizing work.

`BleachSanitizerFilter` is an html5lib filter and can be used anywhere you can use an html5lib filter.

class `bleach.sanitizer.``BleachSanitizerFilter`(source, attributes={'a': ['href', 'title'], 'abbr': ['title'], 'acronym': ['title']}, strip_disallowed_elements=False, strip_html_comments=True, **kwargs)

  html5lib Filter that sanitizes text

  This filter can be used anywhere html5lib filters can be used.

  Creates a BleachSanitizerFilter instance

  Parameters:

  - source (Treewalker) – stream
  - tags (list) – allowed list of tags; defaults to `bleach.sanitizer.ALLOWED_TAGS`
  - attributes (dict) – allowed attributes; can be a callable, list or dict; defaults to `bleach.sanitizer.ALLOWED_ATTRIBUTES`
  - styles (list) – allowed list of css styles; defaults to `bleach.sanitizer.ALLOWED_STYLES`
  - protocols (list) – allowed list of protocols for links; defaults to `bleach.sanitizer.ALLOWED_PROTOCOLS`
  - strip_disallowed_elements (bool) – whether or not to strip disallowed elements
  - strip_html_comments (bool) – whether or not to strip HTML comments

New in version 2.0.