General

Lines should usually not extend past column 79, excepting URLs and similar circumstances. Tab characters must never appear in the document at all.

Section Headings

PEP headings must begin in column zero and the initial letter of each word must be capitalized as in book titles. Acronyms should be in all capitals. Section titles must be adorned with an underline, a single repeated punctuation character, which begins in column zero and must extend at least as far as the right edge of the title text (4 characters minimum). First-level section titles are underlined with “=” (equals signs), second-level section titles with “-” (hyphens), and third-level section titles with “’” (single quotes or apostrophes). For example:

First-Level Title
=================

Second-Level Title
------------------

Third-Level Title
'''''''''''''''''

If there are more than three levels of sections in your PEP, you may insert overline/underline-adorned titles for the first and second levels as follows:

============================
First-Level Title (optional)
============================

-----------------------------
Second-Level Title (optional)
-----------------------------

Third-Level Title
=================

Fourth-Level Title
------------------

Fifth-Level Title
'''''''''''''''''

You shouldn’t have more than five levels of sections in your PEP. If you do, you should consider rewriting it.

You must use two blank lines between the last line of a section’s body and the next section heading. If a subsection heading immediately follows a section heading, a single blank line in-between is sufficient.

The body of each section is not normally indented, although some constructs do use indentation, as described below. Blank lines are used to separate constructs.

Paragraphs

Paragraphs are left-aligned text blocks separated by blank lines. Paragraphs are not indented unless they are part of an indented construct (such as a block quote or a list item).

Inline Markup

Portions of text within paragraphs and other text blocks may be styled. For example:

Text may be marked as *emphasized* (single asterisk markup,
typically shown in italics) or **strongly emphasized** (double
asterisks, typically boldface).  ``Inline literals`` (using double
backquotes) are typically rendered in a monospaced typeface.  No
further markup recognition is done within the double backquotes,
so they're safe for any kind of code snippets.

Block Quotes

Block quotes consist of indented body elements. For example:

This is a paragraph.

    This is a block quote.

    A block quote may contain many paragraphs.

Block quotes are used to quote extended passages from other sources. Block quotes may be nested inside other body elements. Use 4 spaces per indent level.

Literal Blocks

Literal blocks are used for code samples and other preformatted text. To indicate a literal block, preface the indented text block with “::” (two colons), or use the .. code-block:: directive. Indent the text block by 4 spaces; the literal block continues until the end of the indentation. For example:

This is a typical paragraph.  A literal block follows.

::

    for a in [5, 4, 3, 2, 1]:  # this is program code, shown as-is
        print(a)
    print("it's...")

“::” is also recognized at the end of any paragraph; if not immediately preceded by whitespace, one colon will remain visible in the final output:

This is an example::

    Literal block

By default, literal blocks will be syntax-highlighted as Python code. For specific blocks that contain code or data in other languages/formats, use the .. code-block:: language directive, substituting the “short name” of the appropriate Pygments lexer (or text to disable highlighting) for language. For example:

.. code-block:: rst

    An example of the ``rst`` lexer (i.e. *reStructuredText*).

For PEPs that predominantly contain literal blocks of a specific language, use the .. highlight:: language directive with the appropriate language at the top of the PEP body (below the headers and above the Abstract). All literal blocks will then be treated as that language, unless specified otherwise in the specific .. code-block. For example:

.. highlight:: c

Abstract
========

Here's some C code::

    printf("Hello, World!\n");

Lists

Bullet list items begin with one of “-”, “*”, or “+” (hyphen, asterisk, or plus sign), followed by whitespace and the list item body. List item bodies must be left-aligned and indented relative to the bullet; the text immediately after the bullet determines the indentation. For example:

This paragraph is followed by a list.

* This is the first bullet list item.  The blank line above the
  first list item is required; blank lines between list items
  (such as below this paragraph) are optional.

* This is the first paragraph in the second item in the list.

  This is the second paragraph in the second item in the list.
  The blank line above this paragraph is required.  The left edge
  of this paragraph lines up with the paragraph above, both
  indented relative to the bullet.

  - This is a sublist.  The bullet lines up with the left edge of
    the text blocks above.  A sublist is a new list so requires a
    blank line above and below.

* This is the third item of the main list.

This paragraph is not part of the list.

Enumerated (numbered) list items are similar, but use an enumerator instead of a bullet. Enumerators are numbers (1, 2, 3, …), letters (A, B, C, …; uppercase or lowercase), or Roman numerals (i, ii, iii, iv, …; uppercase or lowercase), formatted with a period suffix (“1.”, “2.”), parentheses (“(1)”, “(2)”), or a right-parenthesis suffix (“1)”, “2)”). For example:

1. As with bullet list items, the left edge of paragraphs must
   align.

2. Each list item may contain multiple paragraphs, sublists, etc.

   This is the second paragraph of the second list item.

   a) Enumerated lists may be nested.
   b) Blank lines may be omitted between list items.

Definition lists are written like this:

what
    Definition lists associate a term with a definition.

how
    The term is a one-line phrase, and the definition is one
    or more paragraphs or body elements, indented relative to
    the term.

Tables

Simple tables are easy and compact:

=====  =====  =======
  A      B    A and B
=====  =====  =======
False  False  False
True   False  False
False  True   False
True   True   True
=====  =====  =======

There must be at least two columns in a table (to differentiate from section titles). Column spans use underlines of hyphens (“Inputs” spans the first two columns):

=====  =====  ======
   Inputs     Output
------------  ------
  A      B    A or B
=====  =====  ======
False  False  False
True   False  True
False  True   True
True   True   True
=====  =====  ======

Text in a first-column cell starts a new row. No text in the first column indicates a continuation line; the rest of the cells may consist of multiple lines. For example:

=====  =========================
col 1  col 2
=====  =========================
1      Second column of row 1.
2      Second column of row 2.
       Second line of paragraph.
3      - Second column of row 3.

       - Second item in bullet
         list (row 3, column 2).
=====  =========================

Hyperlinks

When referencing an external web page in the body of a PEP, you should include the title of the page or a suitable description in the text, with either an inline hyperlink or a separate explicit target with the URL. Do not include bare URLs in the body text of the PEP, and use HTTPS links wherever available.

Hyperlink references use backquotes and a trailing underscore to mark up the reference text; backquotes are optional if the reference text is a single word. For example, to reference a hyperlink target named Python website, you would write:

In this paragraph, we refer to the `Python website`_.

If you intend to only reference a link once, and want to define it inline with the text, insert the link into angle brackets (<>) after the text you want to link, but before the closing backtick, with a space between the text and the opening backtick. You should also use a double-underscore after the closing backtick instead of a single one, which makes it an anonymous reference to avoid conflicting with other target names. For example:

Visit the `website <https://www.python.org/>`__ for more.

If you want to use one link multiple places with different linked text, or want to ensure you don’t have to update your link target names when changing the linked text, include the target name within angle brackets following the text to link, with an underscore after the target name but before the closing angle bracket (or the link will not work). For example:

For further examples, see the `documentation <pydocs_>`_.

An explicit target provides the URL. Put targets in the Footnotes section at the end of the PEP, or immediately after the paragraph with the reference. Hyperlink targets begin with two periods and a space (the “explicit markup start”), followed by a leading underscore, the reference text, a colon, and the URL.

.. _Python web site: https://www.python.org/
.. _pydocs: https://docs.python.org/

The reference text and the target text must match (although the match is case-insensitive and ignores differences in whitespace). Note that the underscore trails the reference text but precedes the target text. If you think of the underscore as a right-pointing arrow, it points away from the reference and toward the target.

Internal and PEP/RFC Links

The same mechanism as hyperlinks can be used for internal references. Every unique section title implicitly defines an internal hyperlink target. We can make a link to the Abstract section like this:

Here is a hyperlink reference to the `Abstract`_ section.  The
backquotes are optional since the reference text is a single word;
we can also just write: Abstract_.

To refer to PEPs or RFCs, always use the :pep: and :rfc: roles, never hardcoded URLs. For example:

See :pep:`1` for more information on how to write a PEP,
and :pep:`the Hyperlink section of PEP 12 <12#hyperlinks>` for how to link.

This renders as:

See PEP 1 for more information on how to write a PEP, and the Hyperlink section of PEP 12 for how to link.

PEP numbers in the text are never padded, and there is a space (not a dash) between “PEP” or “RFC” and the number; the above roles will take care of that for you.

Footnotes

Footnote references consist of a left square bracket, a label, a right square bracket, and a trailing underscore. Instead of a number, use a label of the form “#word”, where “word” is a mnemonic consisting of alphanumerics plus internal hyphens, underscores, and periods (no whitespace or other characters are allowed). For example:

Refer to The TeXbook [#TeXbook]_ for more information.

which renders as

Refer to The TeXbook [1] for more information.

Whitespace must precede the footnote reference. Leave a space between the footnote reference and the preceding word.

Use footnotes for additional notes, explanations and caveats, as well as for references to books and other sources not readily available online. Native reST hyperlink targets or inline hyperlinks in the text should be used in preference to footnotes for including URLs to online resources.

Footnotes begin with “.. ” (the explicit markup start), followed by the footnote marker (no underscores), followed by the footnote body. For example:

.. [#TeXbook] Donald Knuth's *The TeXbook*, pages 195 and 196.

which renders as

[1]

Donald Knuth’s The TeXbook, pages 195 and 196.

Footnotes and footnote references will be numbered automatically, and the numbers will always match.

Images

If your PEP contains a diagram or other graphic, you may include it in the processed output using the image directive:

.. image:: diagram.png

Any browser-friendly graphics format is possible; PNG should be preferred for graphics, JPEG for photos and GIF for animations. Currently, SVG must be avoided due to compatibility issues with the PEP build system.

For accessibility and readers of the source text, you should include a description of the image and any key information contained within using the :alt: option to the image directive:

.. image:: dataflow.png
   :alt: Data flows from the input module, through the "black box"
         module, and finally into (and through) the output module.

Comments

A comment is an indented block of arbitrary text immediately following an explicit markup start: two periods and whitespace. Leave the “..” on a line by itself to ensure that the comment is not misinterpreted as another explicit markup construct. Comments are not visible in the processed document. For example:

..
   This section should be updated in the final PEP.
   Ensure the date is accurate.

Escaping Mechanism

reStructuredText uses backslashes (”\”) to override the special meaning given to markup characters and get the literal characters themselves. To get a literal backslash, use an escaped backslash (”\\”). There are two contexts in which backslashes have no special meaning: literal blocks and inline literals (see Inline Markup above). In these contexts, no markup recognition is done, and a single backslash represents a literal backslash, without having to double up.

If you find that you need to use a backslash in your text, consider using inline literals or a literal block instead.