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Generate static web pages from WSGI apps

Project description


Static web page generator created by the Czech Python community.

What this does

Freezeyt is a static webpage freezer. It takes a Python web application and turns it into a set of files that can be served by a simple server like GitHub Pages or Python's http.server.

Freezeyt is compatible with all Python web frameworks that use the common Web Server Gatweay Interface (WSGI)


Freezeyt requires Python 3.6 or above.

It is highly recommended to create and activate a separate virtual environment for this project. You can use venv, virtualenv, Conda, containers or any other kind of virtual environment.

The tool can be installed using:

$ python -m pip install .


To use freezeyt, you need a Python web application. You can use the example Flask app.

Your WSGI application should be named app. Both the application and Freezeyt must be importable (installed) in your environment.

Run freezeyt with the name of your application and the output directory. For example:

$ python -m freezeyt my_app _build

Freezeyt may overwrite the build directory (here, _build), removing all existing files from it.

For more options, see Configuration below.

Python API

Freezeyt also has a Python API, the freeze function that takes an application to freeze and a configuration dict:

from freezeyt import freeze
freeze(app, config)

The config should be a dict as if read from a YAML configuration file (see Configuration below).


While common options can be given on the command line, you can have full control over the freezing process with a YAML configuration file or a variable with the configuration. You can specify a config file using the -c/--config option, for example:

$ python -m freezeyt my_app _build -c freezeyt.yaml

The configuration variable should be a dictionary. To pass the config variable, use the -C/--import-config option, for example:

$ python -m freezeyt my_app _build -C my_app:freezeyt_config

The following options are configurable:

Module Name

The module that contains the application must be given on the command line. In it, Freezyt looks for the variable app. A different variable can be specified using :.








To outupt the frozen website to a directory, specify the directory name:

output: ./_build/

Or use the full form – using the dir saver:

    type: dir
    dir: ./_build/

If output is not specified in the configuration file, you must specify the oputput directory on the command line. Specifying it both on the command line and in the config file is an error.

If there is any existing content in the output directory, freezeyt will either remove it (if the content looks like a previously frozen website) or raise an error. Best practice is to remove the output directory before freezing.

Output to dict

For testing, Freezeyt can also output to a dictionary. This can be configured with:

    type: dict

This is not useful in the CLI, as the return value is lost.


The URL where the application will be deployed can be specified with:

prefix: http://localhost:8000/



Freezeyt will freeze all pages starting with prefix that it finds.

The prefix can also be specified on thecommand line with e.g.: --prefix=http://localhost:8000/. The CLI argument has priority over the config file.

Extra pages

A list of URLs to “extra” pages within the application can be given using:

    - /extra/
    - /extra2.html

Freezeyt will freeze these pages in addition to those it finds by following links.

Extra pages may also be give on the command line, e.g. --extra-page /extra/ --extra-page /extra2.html. The lists from CLI and the config file are merged together.

You can also specify extra pages using a Python generator, specified using a module name and function name as follows:

    - generator: my_app:generate_extra_pages

The generate_extra_pages function should take the application as argument and return an iterable of URLs.

When using the Python API, a generator for extra pages can be specified directly as a Python object, for example:

config = {
   'extra_pages': [{'generator': my_generator_function}],
another_config = {
   'extra_pages': [my_generator_function],

Extra files

Extra files to be included in the output can be specified, along with their content.

This is useful for configuration of your static server. (For pages that are part of your website, we recommend adding them to your application rather than as extra files.)

For example, the following config will add 3 files to the output:

      ".nojekyll": ''
      config/xyz: abc

You can also specify extra files using Base64 encoding or a file path, like so:

        base64: "YWJjZAASNA=="
        copy_from: included/config2.dat

Extra files cannot be specified on the CLI.

Default MIME type

Freezeyt checks whether the file extensions in its output correspond to the MIME types served by the app. If there's a mismatch, freezeyt fails, because this means a server wouldn't be able to serve the page correctly.

It is possible to specify the MIME type used for files without an extension. For example, if your server of static pages defaults to plain text files, use:



It is possible to register hooks, functions that are called when specific events happen in the freezing process.

For example, if mymodule defines functions start and page_frozen, you can make freezeyt call them using this configuration:


When using the Python API, a function can be used instead of a name like mymodule:start.


The function will be called when the freezing process starts, before any other hooks.

It is passed a FreezeInfo object as argument. The object has the following method:

  • add_url(url): Add the URL to the set of pages to be frozen. If that URL was frozen already, or is outside the prefix, does nothing.


The function will be called whenever a page is saved. It is passed a TaskInfo object as argument. The object has the following attributes:

  • get_a_url(): returns a URL of the page, including prefix. Note that a page may be reachable via several URLs; this function returns an arbitrary one.
  • path: the relative path the content is saved to.
  • freeze_info: a FreezeInfo object. See the start hook for details.

Redirect policy

The redirect_policy option specifies the policy for handling redirects. It can be:

  • 'error' (default): When a redirect response is encountered, freezeyt will abort.
  • 'save': freezeyt will save the body of the redirect page, as if the response was 200. This is meant to be used with redirects in the HTML <meta> tag.
  • 'follow': freezeyt will save content from the redirected location.
  • 'ignore': freezeyt will not save any content for pages that redirect.

For example:

redirect_policy: save

URL finding

freezeyt discovers pages in the application it freezes by scanning the application's pages for links. By default, HTML and CSS pages are scanned this way. It is possible to customize the scanning or turn it off by setting url_finders in the configuration. For example, the default scanners would be specified as:

    text/html: get_html_links
    text/css: get_css_links

Keys in the url_finders dict are MIME types; the values can be:

  • strings in the form "module:function", which name the scanning function to call,
  • strings like get_html_links, which name a function from the freezeyt.url_finders module, or
  • Python functions (if configuring freezeyt from Python rather than YAML).

A scanning function gets these arguments:

  • an open file with the page's contents (call read to get the contents as bytes),
  • the URL of the page, as a string, and
  • the HTTP headers, as a list of (name, value) tuples (as in WSGI).

The function should return an iterator of URLs (as strings) found in the page's contents.

The freezeyt.url_finders module includes the functions get_html_links and get_css_links, which you can call (for example, as fallbacks).

Path generation

It is possible to customize the filenames that URLs are saved under using the path_to_url configuration key, for example:

path_to_url: my_module:path_to_url

The value can be:

  • a strings in the form "module:function", which names the function to call (the function can be omitted along with the colon, and defaults to url_to_path), or
  • a Python function (if configuring freezeyt from Python rather than YAML).

The function receives the path of the URL to save, relative to the prefix, and should return a path to the saved file, relative to the build directory.

The default function, available as freezeyt.url_to_path, adds index.html if the URL path ends with /.

Examples of CLI usage

$ python -m freezeyt my_app _build/
$ python -m freezeyt my_app _build/ --prefix
$ python -m freezeyt my_app _build/ -c config.yaml
$ python -m freezeyt my_app _build/ --prefix --extra-page /extra1/ --extra-page /extra2/
$ python -m freezeyt my_app _build/ --prefix --extra-page /extra1/ --extra-page /extra2/ --config path/to/config.yaml


Are you interested in this project? Awesome! Anyone who wants to be part of this project and who's willing to help us is very welcome. Just started with Python? Good news! We're trying to target mainly the beginner Pythonistas who are seeking opportunities to contribute to (ideally open source) projects and who would like to be part of an open source community which could give them a head start in their (hopefully open source :)) programming careers.

Soo, what if you already have some solid Python-fu? First, there's always something new to learn, and second, we'd appreciate if you could guide the “rookies” and pass on some of the knowledge onto them.

Contributions, issues and feature requests are welcome. Feel free to check out the issues page if you'd like to contribute.

How to contribute

  1. Clone this repository to your local computer:
$ git clone
  1. Then fork this repo to your GitHub account
  2. Add your forked repo as a new remote to your local computer:
$ git remote add <name_your_remote><your_username>/freezeyt
  1. Create new branch at your local computer
$ git branch <name_new_branch>
  1. Switch to your new branch
$ git switch <name_new_branch>
  1. Make some awesome changes in code
  2. Push changes to your forked repo on GitHub
$ git push <your_remote> <your_new_branch>
  1. Finally make a pull request from your GitHub account to origin

  2. Repeat this process until we will have done amazing freezer

Using an in-development copy of freezeyt

  • Set PYTHONPATH to the directory with freezeyt, for example:

    • Unix: export PYTHONPATH="/home/name/freezeyt"
    • Windows: set PYTHONPATH=C:\Users\Name\freezeyt
  • Install the web application you want to freeze. Either:

    • install the application using pip, if possible, or
    • install the application's dependencies and cd to the app's directory.
  • Run freezeyt, for example:

    • python -m freezeyt demo_app_url_for _build --prefix http://freezeyt.test/foo/


For testing the project it's necessary to install additional requirements:

$ python -m pip install .[dev]

To run tests in your current environment, use pytest:

$ python -m pytest

To run tests with multiple Python versions (if you have them installed), install tox using python -m pip install tox and run it:

$ tox

Environ variables for tests

Some test scenarios compare freezeyt's results with expected output. When the files with expected output don't exist yet, they can be created by setting the environment variable TEST_CREATE_EXPECTED_OUTPUT to 1:





If you set the variable to any different value or leave it unset then the files will not be recreated (tests will fail if the files are not up to date).

When output changes, you need to first delete the expected output, regenerate it by running tests with TEST_CREATE_EXPECTED_OUTPUT=1, and check that the difference is correct.

Tools and technologies used

How to watch progress

Unfortunately our progress of development can be watched only in Czech language.

Watch the progress:

Other communication channels and info can be found here:

Freezeyt Blog

We keep a blog about the development of Freezeyt. It is available here.

Be warned: some of it is in the Czech language.

Blog development

The blog was tested on Python version 3.8.

The blog is a Flask application. To run it, install additional dependecies with python -m pip install .[blog]. Then, set the environment variable FLASK_APP to the path of the blog app. Also set FLASK_ENV to "development" for easier debugging. Then, run the Flask server.

  1. On Microsoft Windows:
> python -m pip install .[blog]
> set FLASK_APP=freezeyt_blog/
> set FLASK_ENV=development
> flask run
  1. On UNIX:
$ python -m pip install .[blog]
$ export FLASK_APP=freezeyt_blog/
$ export FLASK_ENV=development
$ flask run

The URL where your blog is running will be printed on the terminal.

Once you're satisfied with how the blog looks, you can freeze it with:

$ python -m freezeyt freezeyt_blog/build

Adding new articles to freezeyt blog

Articles are writen in the Markdown language.

Article - save to directory ../freezeyt/freezeyt_blog/articles

Images to articles - save to directory ../freezeyt/freezeyt_blog/static/images

If te files are saved elsewhere, the blog will not work correctly.


Why did the project start?

The Czech Python community uses a lot of static web pages that are generated from a web application for community purposes. For example, organizing and announcing workshops, courses, or meetups.

The community has been so far relying on Frozen Flask and elsa in order to generate the static web content. The new freezer ought to be used with any arbitrary Python Web application framework (Flask, Django, Tornado, etc.). So the community won't be limited by one web app technology for generating static pages anymore.


See GitHub history for all contributors.


This project is licensed under the MIT License. May it serve you well.

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