Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

MD031 - Fenced code blocks should be surrounded by blank lines

Tags: code, blank_lines

Aliases: blanks-around-fences

This rule is triggered when fenced code blocks are either not preceded or not followed by a blank line:

Some text
```
Code block
```

```
Another code block
```
Some more text

To fix this, ensure that all fenced code blocks have a blank line both before and after (except where the block is at the beginning or end of the document):

Some text

```
Code block
```

```
Another code block
```

Some more text

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will not parse fenced code blocks that don't have blank lines before and after them.

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

MD009 - Trailing spaces

Tags: whitespace

Aliases: no-trailing-spaces

Parameters: br_spaces (number; default: 0)

This rule is triggered on any lines that end with whitespace. To fix this, find the line that is triggered and remove any trailing spaces from the end.

The brspaces parameter allows an exception to this rule for a specific amount of trailing spaces used to insert an explicit line break/br element. For example, set brspaces to 2 to allow exactly 2 spaces at the end of a line.

Note: you have to set brspaces to 2 or higher for this exception to take effect - you can't insert a br element with just a single trailing space, so if you set brspaces to 1, the exception will be disabled, just as if it was set to the default of 0.

MD029 - Ordered list item prefix

Tags: ol

Aliases: ol-prefix

Parameters: style ("one", "ordered"; default "one")

This rule is triggered on ordered lists that do not either start with '1.' or do not have a prefix that increases in numerical order (depending on the configured style, which defaults to 'one').

Example valid list if the style is configured as 'one':

1. Do this.
1. Do that.
1. Done.

Example valid list if the style is configured as 'ordered':

1. Do this.
2. Do that.
3. Done.

Separate top-level function and class definitions with two blank lines.

Method definitions inside a class are separated by a single blank
line.

Extra blank lines may be used (sparingly) to separate groups of
related functions.  Blank lines may be omitted between a bunch of
related one-liners (e.g. a set of dummy implementations).

Use blank lines in functions, sparingly, to indicate logical
sections.

Okay: def a():\n    pass\n\n\ndef b():\n    pass
Okay: def a():\n    pass\n\n\nasync def b():\n    pass
Okay: def a():\n    pass\n\n\n# Foo\n# Bar\n\ndef b():\n    pass
Okay: default = 1\nfoo = 1
Okay: classify = 1\nfoo = 1

E301: class Foo:\n    b = 0\n    def bar():\n        pass
E302: def a():\n    pass\n\ndef b(n):\n    pass
E302: def a():\n    pass\n\nasync def b(n):\n    pass
E303: def a():\n    pass\n\n\n\ndef b(n):\n    pass
E303: def a():\n\n\n\n    pass
E304: @decorator\n\ndef a():\n    pass
E305: def a():\n    pass\na()
E306: def a():\n    def b():\n        pass\n    def c():\n        pass

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Each comma, semicolon or colon should be followed by whitespace.

Okay: [a, b]
Okay: (3,)
Okay: a[1:4]
Okay: a[:4]
Okay: a[1:]
Okay: a[1:4:2]
E231: ['a','b']
E231: foo(bar,baz)
E231: [{'a':'b'}]

Use indent_size (PEP8 says 4) spaces per indentation level.

For really old code that you don't want to mess up, you can continue
to use 8-space tabs.

Okay: a = 1
Okay: if a == 0:\n    a = 1
E111:   a = 1
E114:   # a = 1

Okay: for item in items:\n    pass
E112: for item in items:\npass
E115: for item in items:\n# Hi\n    pass

Okay: a = 1\nb = 2
E113: a = 1\n    b = 2
E116: a = 1\n    # b = 2

Trailing whitespace is superfluous.

The warning returned varies on whether the line itself is blank,
for easier filtering for those who want to indent their blank lines.

Okay: spam(1)\n#
W291: spam(1) \n#
W293: class Foo(object):\n    \n    bang = 12

Continuation lines indentation.

Continuation lines should align wrapped elements either vertically
using Python's implicit line joining inside parentheses, brackets
and braces, or using a hanging indent.

When using a hanging indent these considerations should be applied:
- there should be no arguments on the first line, and
- further indentation should be used to clearly distinguish itself
  as a continuation line.

Okay: a = (\n)
E123: a = (\n    )

Okay: a = (\n    42)
E121: a = (\n   42)
E122: a = (\n42)
E123: a = (\n    42\n    )
E124: a = (24,\n     42\n)
E125: if (\n    b):\n    pass
E126: a = (\n        42)
E127: a = (24,\n      42)
E128: a = (24,\n    42)
E129: if (a or\n    b):\n    pass
E131: a = (\n    42\n 24)

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Use indent_size (PEP8 says 4) spaces per indentation level.

For really old code that you don't want to mess up, you can continue
to use 8-space tabs.

Okay: a = 1
Okay: if a == 0:\n    a = 1
E111:   a = 1
E114:   # a = 1

Okay: for item in items:\n    pass
E112: for item in items:\npass
E115: for item in items:\n# Hi\n    pass

Okay: a = 1\nb = 2
E113: a = 1\n    b = 2
E116: a = 1\n    # b = 2

Trailing blank lines are superfluous.

Okay: spam(1)
W391: spam(1)\n

However the last line should end with a new line (warning W292).

Limit all lines to a maximum of 79 characters.

There are still many devices around that are limited to 80 character
lines; plus, limiting windows to 80 characters makes it possible to
have several windows side-by-side.  The default wrapping on such
devices looks ugly.  Therefore, please limit all lines to a maximum
of 79 characters. For flowing long blocks of text (docstrings or
comments), limiting the length to 72 characters is recommended.

Reports error E501.

Avoid extraneous whitespace around keywords.

Okay: True and False
E271: True and  False
E272: True  and False
E273: True and\tFalse
E274: True\tand False

MD026 - Trailing punctuation in header

Tags: headers

Aliases: no-trailing-punctuation

Parameters: punctuation (string; default ".,;:!?")

This rule is triggered on any header that has a punctuation character as the last character in the line:

# This is a header.

To fix this, remove any trailing punctuation:

# This is a header

Note: The punctuation parameter can be used to specify what characters class as punctuation at the end of the header. For example, you can set it to '.,;:!' to allow headers with question marks in them, such as might be used in an FAQ.