Package genshi :: Package filters :: Module transform :: Class Transformer |

# Class Transformer

    object --+
             |
            Transformer

Stream filter that can apply a variety of different transformations to a stream.

This is achieved by selecting the events to be transformed using XPath, then applying the transformations to the events matched by the path expression. Each marked event is in the form (mark, (kind, data, pos)), where mark can be any of ENTER, INSIDE, EXIT, OUTSIDE, or `None`.

The first three marks match START and END events, and any events contained INSIDE any selected XML/HTML element. A non-element match outside a START/END container (e.g. `text()`) will yield an OUTSIDE mark.

    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')

Transformations act on selected stream events matching an XPath expression. Here's an example of removing some markup (the title, in this case) selected by an expression:

    >>> print(html | Transformer('head/title').remove())
    <html><head/><body>Some <em>body</em> text.</body></html>

Inserted content can be passed in the form of a string, or a markup event stream, which includes streams generated programmatically via the builder module:

    >>> from genshi.builder import tag
    >>> print(html | Transformer('body').prepend(tag.h1('Document Title')))
    <html><head><title>Some Title</title></head><body><h1>Document
    Title</h1>Some <em>body</em> text.</body></html>

Each XPath expression determines the set of tags that will be acted upon by subsequent transformations. In this example we select the `<title>` text, copy it into a buffer, then select the `<body>` element and paste the copied text into the body as `<h1>` enclosed text:

    >>> buffer = StreamBuffer()
    >>> print(html | Transformer('head/title/text()').copy(buffer)
    ...     .end().select('body').prepend(tag.h1(buffer)))
    <html><head><title>Some Title</title></head><body><h1>Some Title</h1>Some
    <em>body</em> text.</body></html>

Transformations can also be assigned and reused, although care must be taken when using buffers, to ensure that buffers are cleared between transforms:

    >>> emphasis = Transformer('body//em').attr('class', 'emphasis')
    >>> print(html | emphasis)
    <html><head><title>Some Title</title></head><body>Some <em
    class="emphasis">body</em> text.</body></html>

Instance Methods
__init__(self, path=`'``.``'`) Construct a new transformation filter. |
Stream |
__call__(self, stream, keep_marks=False) Apply the transform filter to the marked stream. |
apply(self, function) Apply a transformation to the stream. |
Inherited from `object`: `__delattr__`, `__format__`, `__getattribute__`, `__hash__`, `__new__`, `__reduce__`, `__reduce_ex__`, `__repr__`, `__setattr__`, `__sizeof__`, `__str__`, `__subclasshook__`
Selection operations
Transformer |
select(self, path) Mark events matching the given XPath expression, within the current selection. |
Transformer |
invert(self) Invert selection so that marked events become unmarked, and vice versa. |
Transformer |
end(self) End current selection, allowing all events to be selected. |
Deletion operations
Transformer |
empty(self) Empty selected elements of all content. |
Transformer |
remove(self) Remove selection from the stream. |
Direct element operations
Transformer |
unwrap(self) Remove outermost enclosing elements from selection. |
Transformer |
wrap(self, element) Wrap selection in an element. |
Content insertion operations
Transformer |
replace(self, content) Replace selection with content. |
Transformer |
before(self, content) Insert content before selection. |
Transformer |
after(self, content) Insert content after selection. |
Transformer |
prepend(self, content) Insert content after the ENTER event of the selection. |
Transformer |
append(self, content) Insert content before the END event of the selection. |
Attribute manipulation
Transformer |
attr(self, name, value) Add, replace or delete an attribute on selected elements. |
Buffer operations
Transformer |
copy(self, buffer, accumulate=False) Copy selection into buffer. |
Transformer |
cut(self, buffer, accumulate=False) Copy selection into buffer and remove the selection from the stream. |
buffer(self) Buffer the entire stream (can consume a considerable amount of memory). |
Miscellaneous operations
Transformer |
filter(self, filter) Apply a normal stream filter to the selection. |
Transformer |
map(self, function, kind) Applies a function to the `data` element of events of `kind` in the selection. |
Transformer |
substitute(self, pattern, replace, count=1) Replace text matching a regular expression. |
rename(self, name) Rename matching elements. |
Transformer |
trace(self, prefix=`'````'`, fileobj=None) Print events as they pass through the transform. |

Properties
| transforms
Inherited from `object`: `__class__`

Method Details

### __init__(self, path=`'``.``'`) (Constructor) |
Construct a new transformation filter. Parameters: `path` - an XPath expression (as string) or a Path instance Overrides: object.__init__

### __call__(self, stream, keep_marks=False) (Call operator) |
Apply the transform filter to the marked stream. Parameters: `stream` - the marked event stream to filter `keep_marks` - Do not strip transformer selection marks from the stream. Useful for testing. Returns: Stream the transformed stream

### apply(self, function) |
Apply a transformation to the stream. Transformations can be chained, similar to stream filters. Any callable accepting a marked stream can be used as a transform. As an example, here is a simple TEXT event upper-casing transform:
    >>> def upper(stream):
    ...     for mark, (kind, data, pos) in stream:
    ...         if mark and kind is TEXT:
    ...             yield mark, (kind, data.upper(), pos)
    ...         else:
    ...             yield mark, (kind, data, pos)
    >>> short_stream = HTML('<body>Some <em>test</em> text</body>')
    >>> print(short_stream | Transformer('.//em/text()').apply(upper))
    <body>Some <em>TEST</em> text</body>

### select(self, path) |
Mark events matching the given XPath expression, within the current selection.
    >>> html = HTML('<body>Some <em>test</em> text</body>')
    >>> print(html | Transformer().select('.//em').trace())
    (None, ('START', (QName('body'), Attrs()), (None, 1, 0)))
    (None, ('TEXT', u'Some ', (None, 1, 6)))
    ('ENTER', ('START', (QName('em'), Attrs()), (None, 1, 11)))
    ('INSIDE', ('TEXT', u'test', (None, 1, 15)))
    ('EXIT', ('END', QName('em'), (None, 1, 19)))
    (None, ('TEXT', u' text', (None, 1, 24)))
    (None, ('END', QName('body'), (None, 1, 29)))
    <body>Some <em>test</em> text</body>
Parameters: `path` - an XPath expression (as string) or a Path instance Returns: Transformer the stream augmented by transformation marks

### invert(self) |
Invert selection so that marked events become unmarked, and vice versa. Specificaly, all marks are converted to null marks, and all null marks are converted to OUTSIDE marks.
    >>> html = HTML('<body>Some <em>test</em> text</body>')
    >>> print(html | Transformer('//em').invert().trace())
    ('OUTSIDE', ('START', (QName('body'), Attrs()), (None, 1, 0)))
    ('OUTSIDE', ('TEXT', u'Some ', (None, 1, 6)))
    (None, ('START', (QName('em'), Attrs()), (None, 1, 11)))
    (None, ('TEXT', u'test', (None, 1, 15)))
    (None, ('END', QName('em'), (None, 1, 19)))
    ('OUTSIDE', ('TEXT', u' text', (None, 1, 24)))
    ('OUTSIDE', ('END', QName('body'), (None, 1, 29)))
    <body>Some <em>test</em> text</body>
Returns: Transformer

### end(self) |
End current selection, allowing all events to be selected. Example:
    >>> html = HTML('<body>Some <em>test</em> text</body>')
    >>> print(html | Transformer('//em').end().trace())
    ('OUTSIDE', ('START', (QName('body'), Attrs()), (None, 1, 0)))
    ('OUTSIDE', ('TEXT', u'Some ', (None, 1, 6)))
    ('OUTSIDE', ('START', (QName('em'), Attrs()), (None, 1, 11)))
    ('OUTSIDE', ('TEXT', u'test', (None, 1, 15)))
    ('OUTSIDE', ('END', QName('em'), (None, 1, 19)))
    ('OUTSIDE', ('TEXT', u' text', (None, 1, 24)))
    ('OUTSIDE', ('END', QName('body'), (None, 1, 29)))
    <body>Some <em>test</em> text</body>
Returns: Transformer the stream augmented by transformation marks

### empty(self) |
Empty selected elements of all content. Example:
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//em').empty())
    <html><head><title>Some Title</title></head><body>Some <em/>
    text.</body></html>
Returns: Transformer

### remove(self) |
Remove selection from the stream. Example:
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//em').remove())
    <html><head><title>Some Title</title></head><body>Some
    text.</body></html>
Returns: Transformer

### unwrap(self) |
Remove outermost enclosing elements from selection. Example:
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//em').unwrap())
    <html><head><title>Some Title</title></head><body>Some body
    text.</body></html>
Returns: Transformer

### wrap(self, element) |
Wrap selection in an element.
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//em').wrap('strong'))
    <html><head><title>Some Title</title></head><body>Some
    <strong><em>body</em></strong> text.</body></html>
Parameters: `element` - either a tag name (as string) or an Element object Returns: Transformer

### replace(self, content) |
Replace selection with content.
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//title/text()').replace('New Title'))
    <html><head><title>New Title</title></head><body>Some <em>body</em>
    text.</body></html>
Parameters: `content` - Either a callable, an iterable of events, or a string to insert. Returns: Transformer

### before(self, content) |
Insert content before selection. In this example we insert the word 'emphasised' before the <em> opening tag:
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//em').before('emphasised '))
    <html><head><title>Some Title</title></head><body>Some emphasised
    <em>body</em> text.</body></html>
Parameters: `content` - Either a callable, an iterable of events, or a string to insert. Returns: Transformer

### after(self, content) |
Insert content after selection. Here, we insert some text after the </em> closing tag:
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//em').after(' rock'))
    <html><head><title>Some Title</title></head><body>Some <em>body</em>
    rock text.</body></html>
Parameters: `content` - Either a callable, an iterable of events, or a string to insert. Returns: Transformer

### prepend(self, content) |
Insert content after the ENTER event of the selection. Inserting some new text at the start of the <body>:
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//body').prepend('Some new body text. '))
    <html><head><title>Some Title</title></head><body>Some new body text.
    Some <em>body</em> text.</body></html>
Parameters: `content` - Either a callable, an iterable of events, or a string to insert. Returns: Transformer

### append(self, content) |
Insert content before the END event of the selection.
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//body').append(' Some new body text.'))
    <html><head><title>Some Title</title></head><body>Some <em>body</em>
    text. Some new body text.</body></html>
Parameters: `content` - Either a callable, an iterable of events, or a string to insert. Returns: Transformer

### attr(self, name, value) |
Add, replace or delete an attribute on selected elements. If `value` evaulates to `None` the attribute will be deleted from the element:
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em class="before">body</em> <em>text</em>.</body>'
    ...             '</html>')
    >>> print(html | Transformer('body/em').attr('class', None))
    <html><head><title>Some Title</title></head><body>Some <em>body</em>
    <em>text</em>.</body></html>
Otherwise the attribute will be set to `value`:
    >>> print(html | Transformer('body/em').attr('class', 'emphasis'))
    <html><head><title>Some Title</title></head><body>Some <em
    class="emphasis">body</em> <em class="emphasis">text</em>.</body></html>
If `value` is a callable it will be called with the attribute name and the START event for the matching element. Its return value will then be used to set the attribute:
    >>> def print_attr(name, event):
    ...     attrs = event[1][1]
    ...     print(attrs)
    ...     return attrs.get(name)
    >>> print(html | Transformer('body/em').attr('class', print_attr))
    Attrs([(QName('class'), u'before')])
    Attrs()
    <html><head><title>Some Title</title></head><body>Some <em
    class="before">body</em> <em>text</em>.</body></html>
Parameters: `name` - the name of the attribute `value` - the value that should be set for the attribute. Returns: Transformer

### copy(self, buffer, accumulate=False) |
Copy selection into buffer. The buffer is replaced by each contiguous selection before being passed to the next transformation. If accumulate=True, further selections will be appended to the buffer rather than replacing it.
    >>> from genshi.builder import tag
    >>> buffer = StreamBuffer()
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('head/title/text()').copy(buffer)
    ...     .end().select('body').prepend(tag.h1(buffer)))
    <html><head><title>Some Title</title></head><body><h1>Some
    Title</h1>Some <em>body</em> text.</body></html>
This example illustrates that only a single contiguous selection will be buffered:
    >>> print(html | Transformer('head/title/text()').copy(buffer)
    ...     .end().select('body/em').copy(buffer).end().select('body')
    ...     .prepend(tag.h1(buffer)))
    <html><head><title>Some Title</title></head><body><h1>Some
    Title</h1>Some <em>body</em> text.</body></html>
    >>> print(buffer)
    <em>body</em>
Element attributes can also be copied for later use:
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body><em>Some</em> <em class="before">body</em>'
    ...             '<em>text</em>.</body></html>')
    >>> buffer = StreamBuffer()
    >>> def apply_attr(name, entry):
    ...     return list(buffer)[0][1][1].get('class')
    >>> print(html | Transformer('body/em[@class]/@class').copy(buffer)
    ...     .end().buffer().select('body/em[not(@class)]')
    ...     .attr('class', apply_attr))
    <html><head><title>Some Title</title></head><body><em
    class="before">Some</em> <em class="before">body</em><em
    class="before">text</em>.</body></html>
Parameters: `buffer` - the StreamBuffer in which the selection should be stored Returns: Transformer Note: Copy (and cut) copy each individual selected object into the buffer before passing to the next transform. For example, the XPath `*|text()` will select all elements and text, each instance of which will be copied to the buffer individually before passing to the next transform. This has implications for how `StreamBuffer` objects can be used, so some experimentation may be required.

### cut(self, buffer, accumulate=False) |
Copy selection into buffer and remove the selection from the stream.
    >>> from genshi.builder import tag
    >>> buffer = StreamBuffer()
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...             '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('.//em/text()').cut(buffer)
    ...     .end().select('.//em').after(tag.h1(buffer)))
    <html><head><title>Some Title</title></head><body>Some
    <em/><h1>body</h1> text.</body></html>
Specifying accumulate=True, appends all selected intervals onto the buffer. Combining this with the .buffer() operation allows us operate on all copied events rather than per-segment. See the documentation on buffer() for more information. Parameters: `buffer` - the StreamBuffer in which the selection should be stored Returns: Transformer Note: this transformation will buffer the entire input stream

### buffer(self) |
Buffer the entire stream (can consume a considerable amount of memory). Useful in conjunction with copy(accumulate=True) and cut(accumulate=True) to ensure that all marked events in the entire stream are copied to the buffer before further transformations are applied. For example, to move all <note> elements inside a <notes> tag at the top of the document:
    >>> doc = HTML('<doc><notes></notes><body>Some <note>one</note> '
    ...            'text <note>two</note>.</body></doc>')
    >>> buffer = StreamBuffer()
    >>> print(doc | Transformer('body/note').cut(buffer, accumulate=True)
    ...     .end().buffer().select('notes').prepend(buffer))
    <doc><notes><note>one</note><note>two</note></notes><body>Some  text
    .</body></doc>

### filter(self, filter) |
Apply a normal stream filter to the selection. The filter is called once for each contiguous block of marked events.
    >>> from genshi.filters.html import HTMLSanitizer
    >>> html = HTML('<html><body>Some text<script>alert(document.cookie)'
    ...             '</script> and some more text</body></html>')
    >>> print(html | Transformer('body/*').filter(HTMLSanitizer()))
    <html><body>Some text and some more text</body></html>
Parameters: `filter` - The stream filter to apply. Returns: Transformer

### map(self, function, kind) |
Applies a function to the `data` element of events of `kind` in the selection.
    >>> html = HTML('<html><head><title>Some Title</title></head>'
    ...               '<body>Some <em>body</em> text.</body></html>')
    >>> print(html | Transformer('head/title').map(unicode.upper, TEXT))
    <html><head><title>SOME TITLE</title></head><body>Some <em>body</em>
    text.</body></html>
Parameters: `function` - the function to apply `kind` - the kind of event the function should be applied to Returns: Transformer

### substitute(self, pattern, replace, count=1) |
Replace text matching a regular expression. Refer to the documentation for `re.sub()` for details.
    >>> html = HTML('<html><body>Some text, some more text and '
    ...             '<b>some bold text</b>\n'
    ...             '<i>some italicised text</i></body></html>')
    >>> print(html | Transformer('body/b').substitute('(?i)some', 'SOME'))
    <html><body>Some text, some more text and <b>SOME bold text</b>
    <i>some italicised text</i></body></html>
    >>> tags = tag.html(tag.body('Some text, some more text and\n',
    ...      Markup('<b>some bold text</b>')))
    >>> print(tags.generate() | Transformer('body').substitute(
    ...     '(?i)some', 'SOME'))
    <html><body>SOME text, some more text and
    <b>SOME bold text</b></body></html>
Parameters: `pattern` - A regular expression object or string. `replace` - Replacement pattern. `count` - Number of replacements to make in each text fragment. Returns: Transformer

### trace(self, prefix=`'````'`, fileobj=None) |
Print events as they pass through the transform.
    >>> html = HTML('<body>Some <em>test</em> text</body>')
    >>> print(html | Transformer('em').trace())
    (None, ('START', (QName('body'), Attrs()), (None, 1, 0)))
    (None, ('TEXT', u'Some ', (None, 1, 6)))
    ('ENTER', ('START', (QName('em'), Attrs()), (None, 1, 11)))
    ('INSIDE', ('TEXT', u'test', (None, 1, 15)))
    ('EXIT', ('END', QName('em'), (None, 1, 19)))
    (None, ('TEXT', u' text', (None, 1, 24)))
    (None, ('END', QName('body'), (None, 1, 29)))
    <body>Some <em>test</em> text</body>
Parameters: `prefix` - a string to prefix each event with in the output `fileobj` - the writable file-like object to write to; defaults to the standard output stream Returns: Transformer