# CodeHilite

## Summary

The CodeHilite extension adds code/syntax highlighting to standard Python-Markdown code blocks using Pygments.

This extension is included in the standard Markdown library.

Note

This extension is in maintenance mode. We will continue to fix bugs and keep it up-to-date with the core parser, but no new features or changes in behavior will be made. If you need a feature that this extension does not offer, then you have three options (1) find an existing third-party extension which meets your needs, (2) build your own extension, or (3) fork this extension (pursuant to its licensing requirements) and maintain it as a third-party extension.

We recommend Highlight as an actively developed alternative.

## Setup

### Step 1: Download and Install Pygments

You will also need to download and install the Pygments package on your `PYTHONPATH`. The CodeHilite extension will produce HTML output without Pygments, but it won’t highlight anything (same behavior as setting `use_pygments` to `False`).

### Step 2: Add CSS Classes

You will need to define the appropriate CSS classes with appropriate rules. The CSS rules either need to be defined in or linked from the header of your HTML templates. Pygments can generate CSS rules for you. Just run the following command from the command line:

    pygmentize -S default -f html -a .codehilite > styles.css

If you are using a different `css_class` (default: `.codehilite`), then set the value of the `-a` option to that class name. The CSS rules will be written to the `styles.css` file which you can copy to your site and link from your HTML templates.

If you would like to use a different theme, swap out `default` for the desired theme. For a list of themes installed on your system (additional themes can be installed via Pygments plugins), run the following command:

    pygmentize -L style

See Pygments’ excellent documentation for more details. If no language is defined, Pygments will attempt to guess the language. When that fails, the code block will not be highlighted.

See Also

GitHub user richeland has provided a number of different CSS style sheets which work with Pygments along with a preview of each theme. The `css_class` used is `.highlight`. Therefore, one would need to override the `css_class` option when using richeland’s CSS styles. However, the Python-Markdown project makes no guarantee that richeland’s CSS styles will work with the version of Pygments you are using. To ensure complete compatibility, you should generate the CSS rules from your own installation of Pygments.

## Syntax

The CodeHilite extension follows the same syntax as regular Markdown code blocks, with one exception. The highlighter needs to know what language to use for the code block. There are three ways to tell the highlighter what language the code block contains and each one has a different result.

Note

The format of the language identifier only effects the display of line numbers if `linenums` is set to `None` (the default). If set to `True` or `False` (see Usage below) the format of the identifier has no effect on the display of line numbers – it only serves as a means to define the language of the code block.

### Shebang (with path)

If the first line of the code block contains a shebang, the language is derived from that and line numbers are used.

        #!/usr/bin/python
        # Code goes here ...

Will result in:

    1
    2

    #!/usr/bin/python
    # Code goes here ...

### Shebang (no path)

If the first line contains a shebang, but the shebang line does not contain a path (a single `/` or even a space), then that line is removed from the code block before processing. Line numbers are used.

        #!python
        # Code goes here ...

Will result in:

    1

    # Code goes here ...

### Colons

If the first line begins with three or more colons, the text following the colons identifies the language. The first line is removed from the code block before processing and line numbers are not used.

        :::python
        # Code goes here ...

Will result in:

    # Code goes here ...

Certain lines can be selected for emphasis with the colon syntax. When using Pygments’ default CSS styles, emphasized lines have a yellow background. This is useful to direct the reader’s attention to specific lines.

        :::python hl_lines="1 3"
        # This line is emphasized
        # This line isn't
        # This line is emphasized

Will result in:

    # This line is emphasized
    # This line isn't
    # This line is emphasized

Note

`hl_lines` is named for Pygments’ option meaning “highlighted lines”.

### When No Language is Defined

CodeHilite is completely backwards compatible so that if a code block is encountered that does not define a language, the block is simply wrapped in `<pre>` tags and output.

        # Code goes here ...

Will result in:

    # Code goes here ...

Lets see the source for that:

    <div class="codehilite"><pre><code># Code goes here ...
    </code></pre></div>

Note

When no language is defined, the Pygments highlighting engine will try to guess the language (unless `guess_lang` is set to `False`). Upon failure, the same behavior will happen as described above.

## Usage

See Extensions for general extension usage. Use `codehilite` as the name of the extension.

See the Library Reference for information about configuring extensions.

The following options are provided to configure the output:

- `linenums`: An alias to Pygments’ `linenos` formatter option. Possible values are `True` for yes, `False` for no and `None` for auto. Defaults to `None`.

  Using `True` will force every code block to have line numbers, even when using colons (`:::`) for language identification.

  Using `False` will turn off all line numbers, even when using shebangs (`#!`) for language identification.

- `guess_lang`: Automatic language detection. Defaults to `True`.

  Using `False` will prevent Pygments from guessing the language, and thus highlighting blocks only when you explicitly set the language.

- `css_class`: An alias to Pygments `cssclass` formatter option. Set CSS class name for the wrapper `<div>` tag. Defaults to `codehilite`.

- `pygments_style`: Pygments HTML Formatter Style (`ColorScheme`). Defaults to `default`.

  Note

  This is useful only when `noclasses` is set to `True`, otherwise the CSS styles must be provided by the end user.

- `noclasses`: Use inline styles instead of CSS classes. Defaults to `False`.

- `use_pygments`: Specifies the use of Pygments in generating the output.

  If `True` (the default) and Pygments is available, CodeHilite will use Pygments to analyze and format the output. Additionally, if using Pygments >= 2.4, the output will be wrapped in `<code>` tags, whereas earlier versions will not.

  Otherwise, Pygments will not be used. If a language is defined for a code block, it will be assigned to the `<code>` tag as a class in the manner suggested by the HTML5 spec and may be used by a JavaScript library in the browser to highlight the code block. See the `lang_prefix` option to customize the prefix.

- `lang_prefix`: The prefix prepended to the language class assigned to the HTML `<code>` tag. Default: `language-`.

- `pygments_formatter`: This option can be used to change the Pygments formatter used for highlighting code blocks. By default, this is set to the string `'html'`, which means it’ll use the default `HtmlFormatter` provided by Pygments.

  This can be set to a string representing any of the other default formatters, or set to a formatter class (or any callable).

  The code’s language is always passed to the formatter as an extra option `lang_str`, with the value formatted as `{lang_prefix}{lang}`. If the language is unspecified, the language guessed by Pygments will be used. While this option has no effect to the Pygments’s builtin formatters, a user can make use of the language in their custom formatter. See an example below.

  To see what formatters are available and how to subclass an existing formatter, please visit Pygments documentation on this topic.

- Any other Pygments’ options:

  All other options are accepted and passed on to Pygments’ lexer and formatter. Therefore, valid options include any options which are accepted by the html formatter or whichever lexer the code’s language uses. Invalid options are ignored without error.

A trivial example:

    markdown.markdown(some_text, extensions=['codehilite'])

To keep the code block’s language in the Pygments generated HTML output, one can provide a custom Pygments formatter that takes the `lang_str` option. For example,

    from pygments.formatters import HtmlFormatter
    from markdown.extensions.codehilite import CodeHiliteExtension

    class CustomHtmlFormatter(HtmlFormatter):
        def __init__(self, lang_str='', **options):
            super().__init__(**options)
            # lang_str has the value {lang_prefix}{lang}
            # specified by the CodeHilite's options
            self.lang_str = lang_str

        def _wrap_code(self, source):
            yield 0, f'<code class="{self.lang_str}">'
            yield from source
            yield 0, '</code>'

    some_text = '''\
        :::python
        print('hellow world')
    '''

    markdown.markdown(
        some_text,
        extensions=[CodeHiliteExtension(pygments_formatter=CustomHtmlFormatter)],
    )

The formatter above will output the following HTML structure for a code block:

    <div class="codehilite">
        <pre>
            <code class="language-python">
            ...
            </code>
        </pre>
    </div>