premailer


Namepremailer JSON
Version 3.10.0 PyPI version JSON
download
home_pagehttp://github.com/peterbe/premailer
SummaryTurns CSS blocks into style attributes
upload_time2021-08-02 20:32:54
maintainer
docs_urlNone
authorPeter Bengtsson
requires_python
licensePython
keywords html lxml email mail style
VCS
bugtrack_url
requirements No requirements were recorded.
Travis-CI No Travis.
coveralls test coverage
            premailer
=========

.. image:: https://travis-ci.org/peterbe/premailer.svg?branch=master
  :target: https://travis-ci.org/peterbe/premailer

.. image:: https://badge.fury.io/py/premailer.svg
  :target: https://pypi.python.org/pypi/premailer

.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
  :target: https://github.com/ambv/black

Looking for sponsors
--------------------

This project is actively looking for corporate sponsorship. If you want
to help making this an active project consider `pinging
Peter <https://www.peterbe.com/contact>`__ and we can talk about putting
up logos and links to your company.

Python versions
---------------

Our
`tox.ini <https://github.com/peterbe/premailer/blob/master/tox.ini>`__
makes sure premailer works in:

-  Python 3.4
-  Python 3.5
-  Python 3.6
-  Python 3.7
-  Python 3.8
-  PyPy

Turns CSS blocks into style attributes
--------------------------------------

When you send HTML emails you can't use style tags but instead you have
to put inline ``style`` attributes on every element. So from this:

.. code:: html

    <html>
    <style type="text/css">
    h1 { border:1px solid black }
    p { color:red;}
    </style>
    <h1 style="font-weight:bolder">Peter</h1>
    <p>Hej</p>
    </html>

You want this:

.. code:: html

    <html>
    <h1 style="font-weight:bolder; border:1px solid black">Peter</h1>
    <p style="color:red">Hej</p>
    </html>

premailer does this. It parses an HTML page, looks up ``style`` blocks
and parses the CSS. It then uses the ``lxml.html`` parser to modify the
DOM tree of the page accordingly.

Warning!
By default, premailer will attempt to download any external stylesheets by URL over the Internet.
If you want to prevent this you can use the ``allow_network=False`` option.

Getting started
---------------

If you haven't already done so, install ``premailer`` first:

::

    $ pip install premailer

Next, the most basic use is to use the shortcut function, like this:

.. code:: python

    >>> from premailer import transform
    >>> print(transform("""
    ...         <html>
    ...         <style type="text/css">
    ...         h1 { border:1px solid black }
    ...         p { color:red;}
    ...         p::first-letter { float:left; }
    ...         </style>
    ...         <style type="text/css" data-premailer="ignore">
    ...         h1 { color:blue; }
    ...         </style>
    ...         <h1 style="font-weight:bolder">Peter</h1>
    ...         <p>Hej</p>
    ...         </html>
    ... """))
    <html>
    <head>
        <style type="text/css">p::first-letter {float:left}</style>
        <style type="text/css">
        h1 { color:blue; }
        </style>
    </head>
    <body>
        <h1 style="border:1px solid black; font-weight:bolder">Peter</h1>
        <p style="color:red">Hej</p>
    </body>
    </html>

The ``transform`` shortcut function transforms the given HTML using the defaults for all options:

.. code:: python

    base_url=None, # Optional URL prepended to all relative links (both stylesheets and internal)
    disable_link_rewrites=False, # Allow link rewrites (e.g. using base_url)
    preserve_internal_links=False, # Do not preserve links to named anchors when using base_url
    preserve_inline_attachments=True, # Preserve links with cid: scheme when base_url is specified
    preserve_handlebar_syntax=False # Preserve handlebar syntax from being encoded
    exclude_pseudoclasses=True, # Ignore pseudoclasses when processing styles
    keep_style_tags=False, # Discard original style tag
    include_star_selectors=False, # Ignore star selectors when processing styles
    remove_classes=False, # Leave class attributes on HTML elements
    capitalize_float_margin=False, # Do not capitalize float and margin properties
    strip_important=True, # Remove !important from property values
    external_styles=None, # Optional list of URLs to load and parse
    css_text=None, # Optional CSS text to parse
    method="html", # Parse input as HTML (as opposed to "xml")
    base_path=None, # Optional base path to stylesheet in your file system
    disable_basic_attributes=None, # Optional list of attribute names to preserve on HTML elements
    disable_validation=False, # Validate CSS when parsing it with cssutils
    cache_css_parsing=True, # Do cache parsed output for CSS
    cssutils_logging_handler=None, # See "Capturing logging from cssutils" below
    cssutils_logging_level=None,
    disable_leftover_css=False, # Output CSS that was not inlined into the HEAD
    align_floating_images=True, # Add align attribute for floated images
    remove_unset_properties=True # Remove CSS properties if their value is unset when merged
    allow_network=True # allow network access to fetch linked css files
    allow_insecure_ssl=False # Don't allow unverified SSL certificates for external links
    allow_loading_external_files=False # Allow loading any non-HTTP external file URL
    session=None # Session used for http requests - supply your own for caching or to provide authentication

For more advanced options, check out the code of the ``Premailer`` class
and all its options in its constructor.

You can also use premailer from the command line by using its main
module.

::

    $ python -m premailer -h
    usage: python -m premailer [options]

    optional arguments:
    -h, --help            show this help message and exit
    -f [INFILE], --file [INFILE]
                          Specifies the input file. The default is stdin.
    -o [OUTFILE], --output [OUTFILE]
                          Specifies the output file. The default is stdout.
    --base-url BASE_URL
    --remove-internal-links PRESERVE_INTERNAL_LINKS
                          Remove links that start with a '#' like anchors.
    --exclude-pseudoclasses
                          Pseudo classes like p:last-child', p:first-child, etc
    --preserve-style-tags
                          Do not delete <style></style> tags from the html
                          document.
    --remove-star-selectors
                          All wildcard selectors like '* {color: black}' will be
                          removed.
    --remove-classes      Remove all class attributes from all elements
    --strip-important     Remove '!important' for all css declarations.
    --method METHOD       The type of html to output. 'html' for HTML, 'xml' for
                          XHTML.
    --base-path BASE_PATH
                          The base path for all external stylsheets.
    --external-style EXTERNAL_STYLES
                          The path to an external stylesheet to be loaded.
    --disable-basic-attributes DISABLE_BASIC_ATTRIBUTES
                          Disable provided basic attributes (comma separated)
    --disable-validation  Disable CSSParser validation of attributes and values
    --pretty              Pretty-print the outputted HTML.
    --allow-insecure-ssl  Skip SSL certificate verification for external URLs.
    --allow-loading-external-files Allow opening any non-HTTP external file URL.

A basic example:

::

    $ python -m premailer --base-url=http://google.com/ -f newsletter.html
    <html>
    <head><style>.heading { color:red; }</style></head>
    <body><h1 class="heading" style="color:red"><a href="http://google.com/">Title</a></h1></body>
    </html>

The command line interface supports standard input.

::

    $ echo '<style>.heading { color:red; }</style><h1 class="heading"><a href="/">Title</a></h1>' | python -m premailer --base-url=http://google.com/
    <html>
    <head><style>.heading { color:red; }</style></head>
    <body><h1 class="heading" style="color:red"><a href="http://google.com/">Title</a></h1></body>
    </html>

Turning relative URLs into absolute URLs
----------------------------------------

Another thing premailer can do for you is to turn relative URLs (e.g.
"/some/page.html" into "http://www.peterbe.com/some/page.html"). It does
this to all ``href`` and ``src`` attributes that don't have a ``://``
part in it. For example, turning this:

.. code:: html

    <html>
    <body>
    <a href="/">Home</a>
    <a href="page.html">Page</a>
    <a href="http://crosstips.org">External</a>
    <img src="/folder/">Folder</a>
    </body>
    </html>

Into this:

.. code:: html

    <html>
    <body>
    <a href="http://www.peterbe.com/">Home</a>
    <a href="http://www.peterbe.com/page.html">Page</a>
    <a href="http://crosstips.org">External</a>
    <img src="http://www.peterbe.com/folder/">Folder</a>
    </body>
    </html>

by using ``transform('...', base_url='http://www.peterbe.com/')``.

Ignore certain ``<style>`` or ``<link>`` tags
---------------------------------------------

Suppose you have a style tag that you don't want to have processed and
transformed you can simply set a data attribute on the tag like:

.. code:: html

    <head>
    <style>/* this gets processed */</style>
    <style data-premailer="ignore">/* this gets ignored */</style>
    </head>

That tag gets completely ignored except when the HTML is processed, the
attribute ``data-premailer`` is removed.

It works equally for a ``<link>`` tag like:

.. code:: html

    <head>
    <link rel="stylesheet" href="foo.css" data-premailer="ignore">
    </head>

HTML attributes created additionally
------------------------------------

Certain HTML attributes are also created on the HTML if the CSS contains
any ones that are easily translated into HTML attributes. For example,
if you have this CSS: ``td { background-color:#eee; }`` then this is
transformed into ``style="background-color:#eee"`` and as an HTML
attribute ``bgcolor="#eee"``.

Having these extra attributes basically as a "back up" for really shit
email clients that can't even take the style attributes. A lot of
professional HTML newsletters such as Amazon's use this. You can disable
some attributes in ``disable_basic_attributes``.


Capturing logging from ``cssutils``
-----------------------------------

`cssutils <https://pypi.python.org/pypi/cssutils/>`__ is the library that
``premailer`` uses to parse CSS. It will use the python ``logging`` module
to mention all issues it has with parsing your CSS. If you want to capture
this, you have to pass in ``cssutils_logging_handler`` and
``cssutils_logging_level`` (optional). For example like this:

.. code:: python

    >>> import logging
    >>> import premailer
    >>> from io import StringIO
    >>> mylog = StringIO()
    >>> myhandler = logging.StreamHandler(mylog)
    >>> p = premailer.Premailer(
    ...     cssutils_logging_handler=myhandler,
    ...     cssutils_logging_level=logging.INFO
    ... )
    >>> result = p.transform("""
    ...         <html>
    ...         <style type="text/css">
    ...         @keyframes foo { from { opacity: 0; } to { opacity: 1; } }
    ...         </style>
    ...         <p>Hej</p>
    ...         </html>
    ... """)
    >>> mylog.getvalue()
    'CSSStylesheet: Unknown @rule found. [2:1: @keyframes]\n'


If execution speed is on your mind
----------------------------------

If execution speed is important, it's very plausible that you're not just converting
1 HTML document but *a lot* of HTML documents. Then, the first thing you should do
is avoid using the ``premailer.transform`` function because it creates a ``Premailer``
class instance every time.

.. code:: python

    # WRONG WAY!
    from premailer import transform

    for html_string in get_html_documents():
        transformed = transform(html_string, base_url=MY_BASE_URL)
        # do something with 'transformed'

Instead...

.. code:: python

    # RIGHT WAY
    from premailer import Premailer

    instance = Premailer(base_url=MY_BASE_URL)
    for html_string in get_html_documents():
        transformed = instance.transform(html_string)
        # do something with 'transformed'

Another thing to watch out for when you're reusing the same imported Python code
and reusing it is that internal memoize function caches might build up. The
environment variable to control is ``PREMAILER_CACHE_MAXSIZE``. This parameter
requires a little bit of fine-tuning and calibration if your workload is really
big and memory even becomes an issue.

Advanced options
----------------

Below are some advanced configuration options that probably doesn't matter for
most people with regular load.

Choosing the cache implementation
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

By default, ``premailer`` uses `LFUCache
<https://cachetools.readthedocs.io/en/latest/#cachetools.LFUCache>`__ to cache
selectors, styles and parsed CSS strings. If LFU doesn't serve your purpose, it
is possible to switch to an alternate implementation using below environment
variables.

- ``PREMAILER_CACHE``: Can be LRU, LFU or TTL. Default is LFU.
- ``PREMAILER_CACHE_MAXSIZE``: Maximum no. of items to be stored in cache. Defaults to 128.
- ``PREMAILER_CACHE_TTL``: Time to live for cache entries. Only applicable for TTL cache. Defaults to 1 hour.


Getting coding
--------------

First clone the code and create whatever virtualenv you need, then run:

.. code:: bash

    pip install -e ".[dev]"


Then to run the tests, run:

.. code:: bash

    tox

This will run the *whole test suite* for every possible version of Python
it can find on your system. To run the tests more incrementally, open
up the ``tox.ini`` and see how it works.

Code style is all black
-----------------------

All code has to be formatted with `Black <https://pypi.org/project/black/>`_
and the best tool for checking this is
`therapist <https://pypi.org/project/therapist/>`_ since it can help you run
all, help you fix things, and help you make sure linting is passing before
you git commit. This project also uses ``flake8`` to check other things
Black can't check.

To check linting with ``tox`` use:

.. code:: bash

    tox -e lint

To install the ``therapist`` pre-commit hook simply run:

.. code:: bash

    therapist install

When you run ``therapist run`` it will only check the files you've touched.
To run it for all files use:

.. code:: bash

    therapist run --use-tracked-files

And to fix all/any issues run:

.. code:: bash

    therapist run --use-tracked-files --fix




            

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    "description": "premailer\n=========\n\n.. image:: https://travis-ci.org/peterbe/premailer.svg?branch=master\n  :target: https://travis-ci.org/peterbe/premailer\n\n.. image:: https://badge.fury.io/py/premailer.svg\n  :target: https://pypi.python.org/pypi/premailer\n\n.. image:: https://img.shields.io/badge/code%20style-black-000000.svg\n  :target: https://github.com/ambv/black\n\nLooking for sponsors\n--------------------\n\nThis project is actively looking for corporate sponsorship. If you want\nto help making this an active project consider `pinging\nPeter <https://www.peterbe.com/contact>`__ and we can talk about putting\nup logos and links to your company.\n\nPython versions\n---------------\n\nOur\n`tox.ini <https://github.com/peterbe/premailer/blob/master/tox.ini>`__\nmakes sure premailer works in:\n\n-  Python 3.4\n-  Python 3.5\n-  Python 3.6\n-  Python 3.7\n-  Python 3.8\n-  PyPy\n\nTurns CSS blocks into style attributes\n--------------------------------------\n\nWhen you send HTML emails you can't use style tags but instead you have\nto put inline ``style`` attributes on every element. So from this:\n\n.. code:: html\n\n    <html>\n    <style type=\"text/css\">\n    h1 { border:1px solid black }\n    p { color:red;}\n    </style>\n    <h1 style=\"font-weight:bolder\">Peter</h1>\n    <p>Hej</p>\n    </html>\n\nYou want this:\n\n.. code:: html\n\n    <html>\n    <h1 style=\"font-weight:bolder; border:1px solid black\">Peter</h1>\n    <p style=\"color:red\">Hej</p>\n    </html>\n\npremailer does this. It parses an HTML page, looks up ``style`` blocks\nand parses the CSS. It then uses the ``lxml.html`` parser to modify the\nDOM tree of the page accordingly.\n\nWarning!\nBy default, premailer will attempt to download any external stylesheets by URL over the Internet.\nIf you want to prevent this you can use the ``allow_network=False`` option.\n\nGetting started\n---------------\n\nIf you haven't already done so, install ``premailer`` first:\n\n::\n\n    $ pip install premailer\n\nNext, the most basic use is to use the shortcut function, like this:\n\n.. code:: python\n\n    >>> from premailer import transform\n    >>> print(transform(\"\"\"\n    ...         <html>\n    ...         <style type=\"text/css\">\n    ...         h1 { border:1px solid black }\n    ...         p { color:red;}\n    ...         p::first-letter { float:left; }\n    ...         </style>\n    ...         <style type=\"text/css\" data-premailer=\"ignore\">\n    ...         h1 { color:blue; }\n    ...         </style>\n    ...         <h1 style=\"font-weight:bolder\">Peter</h1>\n    ...         <p>Hej</p>\n    ...         </html>\n    ... \"\"\"))\n    <html>\n    <head>\n        <style type=\"text/css\">p::first-letter {float:left}</style>\n        <style type=\"text/css\">\n        h1 { color:blue; }\n        </style>\n    </head>\n    <body>\n        <h1 style=\"border:1px solid black; font-weight:bolder\">Peter</h1>\n        <p style=\"color:red\">Hej</p>\n    </body>\n    </html>\n\nThe ``transform`` shortcut function transforms the given HTML using the defaults for all options:\n\n.. code:: python\n\n    base_url=None, # Optional URL prepended to all relative links (both stylesheets and internal)\n    disable_link_rewrites=False, # Allow link rewrites (e.g. using base_url)\n    preserve_internal_links=False, # Do not preserve links to named anchors when using base_url\n    preserve_inline_attachments=True, # Preserve links with cid: scheme when base_url is specified\n    preserve_handlebar_syntax=False # Preserve handlebar syntax from being encoded\n    exclude_pseudoclasses=True, # Ignore pseudoclasses when processing styles\n    keep_style_tags=False, # Discard original style tag\n    include_star_selectors=False, # Ignore star selectors when processing styles\n    remove_classes=False, # Leave class attributes on HTML elements\n    capitalize_float_margin=False, # Do not capitalize float and margin properties\n    strip_important=True, # Remove !important from property values\n    external_styles=None, # Optional list of URLs to load and parse\n    css_text=None, # Optional CSS text to parse\n    method=\"html\", # Parse input as HTML (as opposed to \"xml\")\n    base_path=None, # Optional base path to stylesheet in your file system\n    disable_basic_attributes=None, # Optional list of attribute names to preserve on HTML elements\n    disable_validation=False, # Validate CSS when parsing it with cssutils\n    cache_css_parsing=True, # Do cache parsed output for CSS\n    cssutils_logging_handler=None, # See \"Capturing logging from cssutils\" below\n    cssutils_logging_level=None,\n    disable_leftover_css=False, # Output CSS that was not inlined into the HEAD\n    align_floating_images=True, # Add align attribute for floated images\n    remove_unset_properties=True # Remove CSS properties if their value is unset when merged\n    allow_network=True # allow network access to fetch linked css files\n    allow_insecure_ssl=False # Don't allow unverified SSL certificates for external links\n    allow_loading_external_files=False # Allow loading any non-HTTP external file URL\n    session=None # Session used for http requests - supply your own for caching or to provide authentication\n\nFor more advanced options, check out the code of the ``Premailer`` class\nand all its options in its constructor.\n\nYou can also use premailer from the command line by using its main\nmodule.\n\n::\n\n    $ python -m premailer -h\n    usage: python -m premailer [options]\n\n    optional arguments:\n    -h, --help            show this help message and exit\n    -f [INFILE], --file [INFILE]\n                          Specifies the input file. The default is stdin.\n    -o [OUTFILE], --output [OUTFILE]\n                          Specifies the output file. The default is stdout.\n    --base-url BASE_URL\n    --remove-internal-links PRESERVE_INTERNAL_LINKS\n                          Remove links that start with a '#' like anchors.\n    --exclude-pseudoclasses\n                          Pseudo classes like p:last-child', p:first-child, etc\n    --preserve-style-tags\n                          Do not delete <style></style> tags from the html\n                          document.\n    --remove-star-selectors\n                          All wildcard selectors like '* {color: black}' will be\n                          removed.\n    --remove-classes      Remove all class attributes from all elements\n    --strip-important     Remove '!important' for all css declarations.\n    --method METHOD       The type of html to output. 'html' for HTML, 'xml' for\n                          XHTML.\n    --base-path BASE_PATH\n                          The base path for all external stylsheets.\n    --external-style EXTERNAL_STYLES\n                          The path to an external stylesheet to be loaded.\n    --disable-basic-attributes DISABLE_BASIC_ATTRIBUTES\n                          Disable provided basic attributes (comma separated)\n    --disable-validation  Disable CSSParser validation of attributes and values\n    --pretty              Pretty-print the outputted HTML.\n    --allow-insecure-ssl  Skip SSL certificate verification for external URLs.\n    --allow-loading-external-files Allow opening any non-HTTP external file URL.\n\nA basic example:\n\n::\n\n    $ python -m premailer --base-url=http://google.com/ -f newsletter.html\n    <html>\n    <head><style>.heading { color:red; }</style></head>\n    <body><h1 class=\"heading\" style=\"color:red\"><a href=\"http://google.com/\">Title</a></h1></body>\n    </html>\n\nThe command line interface supports standard input.\n\n::\n\n    $ echo '<style>.heading { color:red; }</style><h1 class=\"heading\"><a href=\"/\">Title</a></h1>' | python -m premailer --base-url=http://google.com/\n    <html>\n    <head><style>.heading { color:red; }</style></head>\n    <body><h1 class=\"heading\" style=\"color:red\"><a href=\"http://google.com/\">Title</a></h1></body>\n    </html>\n\nTurning relative URLs into absolute URLs\n----------------------------------------\n\nAnother thing premailer can do for you is to turn relative URLs (e.g.\n\"/some/page.html\" into \"http://www.peterbe.com/some/page.html\"). It does\nthis to all ``href`` and ``src`` attributes that don't have a ``://``\npart in it. For example, turning this:\n\n.. code:: html\n\n    <html>\n    <body>\n    <a href=\"/\">Home</a>\n    <a href=\"page.html\">Page</a>\n    <a href=\"http://crosstips.org\">External</a>\n    <img src=\"/folder/\">Folder</a>\n    </body>\n    </html>\n\nInto this:\n\n.. code:: html\n\n    <html>\n    <body>\n    <a href=\"http://www.peterbe.com/\">Home</a>\n    <a href=\"http://www.peterbe.com/page.html\">Page</a>\n    <a href=\"http://crosstips.org\">External</a>\n    <img src=\"http://www.peterbe.com/folder/\">Folder</a>\n    </body>\n    </html>\n\nby using ``transform('...', base_url='http://www.peterbe.com/')``.\n\nIgnore certain ``<style>`` or ``<link>`` tags\n---------------------------------------------\n\nSuppose you have a style tag that you don't want to have processed and\ntransformed you can simply set a data attribute on the tag like:\n\n.. code:: html\n\n    <head>\n    <style>/* this gets processed */</style>\n    <style data-premailer=\"ignore\">/* this gets ignored */</style>\n    </head>\n\nThat tag gets completely ignored except when the HTML is processed, the\nattribute ``data-premailer`` is removed.\n\nIt works equally for a ``<link>`` tag like:\n\n.. code:: html\n\n    <head>\n    <link rel=\"stylesheet\" href=\"foo.css\" data-premailer=\"ignore\">\n    </head>\n\nHTML attributes created additionally\n------------------------------------\n\nCertain HTML attributes are also created on the HTML if the CSS contains\nany ones that are easily translated into HTML attributes. For example,\nif you have this CSS: ``td { background-color:#eee; }`` then this is\ntransformed into ``style=\"background-color:#eee\"`` and as an HTML\nattribute ``bgcolor=\"#eee\"``.\n\nHaving these extra attributes basically as a \"back up\" for really shit\nemail clients that can't even take the style attributes. A lot of\nprofessional HTML newsletters such as Amazon's use this. You can disable\nsome attributes in ``disable_basic_attributes``.\n\n\nCapturing logging from ``cssutils``\n-----------------------------------\n\n`cssutils <https://pypi.python.org/pypi/cssutils/>`__ is the library that\n``premailer`` uses to parse CSS. It will use the python ``logging`` module\nto mention all issues it has with parsing your CSS. If you want to capture\nthis, you have to pass in ``cssutils_logging_handler`` and\n``cssutils_logging_level`` (optional). For example like this:\n\n.. code:: python\n\n    >>> import logging\n    >>> import premailer\n    >>> from io import StringIO\n    >>> mylog = StringIO()\n    >>> myhandler = logging.StreamHandler(mylog)\n    >>> p = premailer.Premailer(\n    ...     cssutils_logging_handler=myhandler,\n    ...     cssutils_logging_level=logging.INFO\n    ... )\n    >>> result = p.transform(\"\"\"\n    ...         <html>\n    ...         <style type=\"text/css\">\n    ...         @keyframes foo { from { opacity: 0; } to { opacity: 1; } }\n    ...         </style>\n    ...         <p>Hej</p>\n    ...         </html>\n    ... \"\"\")\n    >>> mylog.getvalue()\n    'CSSStylesheet: Unknown @rule found. [2:1: @keyframes]\\n'\n\n\nIf execution speed is on your mind\n----------------------------------\n\nIf execution speed is important, it's very plausible that you're not just converting\n1 HTML document but *a lot* of HTML documents. Then, the first thing you should do\nis avoid using the ``premailer.transform`` function because it creates a ``Premailer``\nclass instance every time.\n\n.. code:: python\n\n    # WRONG WAY!\n    from premailer import transform\n\n    for html_string in get_html_documents():\n        transformed = transform(html_string, base_url=MY_BASE_URL)\n        # do something with 'transformed'\n\nInstead...\n\n.. code:: python\n\n    # RIGHT WAY\n    from premailer import Premailer\n\n    instance = Premailer(base_url=MY_BASE_URL)\n    for html_string in get_html_documents():\n        transformed = instance.transform(html_string)\n        # do something with 'transformed'\n\nAnother thing to watch out for when you're reusing the same imported Python code\nand reusing it is that internal memoize function caches might build up. The\nenvironment variable to control is ``PREMAILER_CACHE_MAXSIZE``. This parameter\nrequires a little bit of fine-tuning and calibration if your workload is really\nbig and memory even becomes an issue.\n\nAdvanced options\n----------------\n\nBelow are some advanced configuration options that probably doesn't matter for\nmost people with regular load.\n\nChoosing the cache implementation\n^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n\nBy default, ``premailer`` uses `LFUCache\n<https://cachetools.readthedocs.io/en/latest/#cachetools.LFUCache>`__ to cache\nselectors, styles and parsed CSS strings. If LFU doesn't serve your purpose, it\nis possible to switch to an alternate implementation using below environment\nvariables.\n\n- ``PREMAILER_CACHE``: Can be LRU, LFU or TTL. Default is LFU.\n- ``PREMAILER_CACHE_MAXSIZE``: Maximum no. of items to be stored in cache. Defaults to 128.\n- ``PREMAILER_CACHE_TTL``: Time to live for cache entries. Only applicable for TTL cache. Defaults to 1 hour.\n\n\nGetting coding\n--------------\n\nFirst clone the code and create whatever virtualenv you need, then run:\n\n.. code:: bash\n\n    pip install -e \".[dev]\"\n\n\nThen to run the tests, run:\n\n.. code:: bash\n\n    tox\n\nThis will run the *whole test suite* for every possible version of Python\nit can find on your system. To run the tests more incrementally, open\nup the ``tox.ini`` and see how it works.\n\nCode style is all black\n-----------------------\n\nAll code has to be formatted with `Black <https://pypi.org/project/black/>`_\nand the best tool for checking this is\n`therapist <https://pypi.org/project/therapist/>`_ since it can help you run\nall, help you fix things, and help you make sure linting is passing before\nyou git commit. This project also uses ``flake8`` to check other things\nBlack can't check.\n\nTo check linting with ``tox`` use:\n\n.. code:: bash\n\n    tox -e lint\n\nTo install the ``therapist`` pre-commit hook simply run:\n\n.. code:: bash\n\n    therapist install\n\nWhen you run ``therapist run`` it will only check the files you've touched.\nTo run it for all files use:\n\n.. code:: bash\n\n    therapist run --use-tracked-files\n\nAnd to fix all/any issues run:\n\n.. code:: bash\n\n    therapist run --use-tracked-files --fix\n\n\n\n",
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