Installation and Startup

Understanding the design

Before everything else it is important to understand that unlike other web frameworks, is not only a python module that can be imported by apps. It is also a program that is in charge of starting some apps. For this reason you need two things:

  • The py4web module (which you download from our web site, from pypi or from github)

  • One or more folders containing collections of apps you want to run.

py4web has command line options to create a folder with some example apps, to initialize an existing folder, and to add scaffolding apps to that folder. Once installed you can have multiple apps under the same folder running concurrently and served by the same py4web process at the same address and port. An apps folder is a python module, and each app is also a python module.

Supported platforms and prerequisites

py4web runs fine on Windows, MacOS and Linux. Its only prerequisite is Python 3.7+, which must be installed in advance (except if you use binaries).

Setup procedures

There are four alternative ways of installing py4web, we will guide you through each of them and if you get stuck, reach out to us.

Installing from pip, using a virtual environment

A full installation of any complex python application like py4web will surely modify the python environment of your system. In order to prevent any unwanted change, it’s a good habit to use a python virtual environment (also called virtualenv, see here for an introduction). This is a standard python feature; if you still don’t know virtualenv it’s a good time to start its discovery!

Here are the instructions for creating the virtual environment, activating it, and installing py4web in it:

python3 -m venv venv
. venv/bin/activate
python -m pip install --upgrade py4web --no-cache-dir
python py4web setup apps
python py4web set_password
python py4web run apps

Starting py4web is same with or without a virtual environment python py4web run apps

Installing from pip, without virtual environment

pip is the basic installation procedure for py4web, it will quickly install the latest stable release of py4web.

From the command line

python3 -m pip install --upgrade py4web --no-cache-dir --user

Also, if python3 does not work, try specify a full version as in python3.8.

This will install py4web and all its dependencies on the system’s path only. The assets folder (that contains the py4web’s system apps) will also be created. After the installation you’ll be able to start py4web on any given working folder with

py4web setup apps
py4web set_password
py4web run apps

If the command py4web is not accepted, it means it’s not in the system’s path. On Windows, a special py4web.exe file (pointing to will be created by pip on the system’s path, but not if you type the –user option by mistake, then you can run the needed commands like this

python3 setup apps
python3 set_password
python3 run apps

Installing from source (globally)

This is the traditional way for installing a program, but it works only on Linux and MacOS (Windows does not normally support the make utility). All the requirements will be installed on the system’s path along with links to the program on the local folder

git clone
cd py4web
make assets
make test
make install
py4web setup apps
py4web set_password
py4web run apps

Also notice that when installing in this way the content of py4web/assets folder is missing at first but it is manually created later with the make assets command.

Notice that you also (and should) install py4web from source inside a virtual environment.

Installing from source (locally)

In this way all the requirements will be installed or upgraded on the system’s path, but py4web itself will only be copied on a local folder. This is especially useful if you already have a working py4web installation but you want to test a different one. Also, installing from sources (locally or globally) will install all the latest changes present on the master branch of py4web - hence you will gain the latest (but potentially untested) code.

From the command line, go to a given working folder and then run

git clone
cd py4web
python3 -m pip install  --upgrade -r requirements.txt

Once installed, you should always start it from there with:

./ setup apps
./ set_password
./ run apps

If you have installed py4web both globally and locally, notice the ./ ; it forces the run of the local folder’s py4web and not the globally installed one.

Installing from binaries

This is not a real installation, because you just copy a bunch of files on your system without modifying it anyhow. Hence this is the simplest solution, especially for beginners or students, because it does not require Python pre-installed on your system nor administrative rights. On the other hand, it’s experimental, it could contain an old py4web release, DAL support is limited and it is quite difficult to add other functionalities to it.

In order to use it you just need to download the latest Windows or MacOS ZIP file from this external repository. Unzip it on a local folder and open a command line there. Finally run

./py4web set_password
./py4web run apps

(omit ‘./’ if you’re using Windows).

Notice: the binaries many not correspond to the latest master or the latest stable branch of py4web although we do our best to keep them up to date.


If you installed py4web from pip you can simple upgrade it with

python3 -m pip install --upgrade py4web


This will not automatically upgrade the standard apps like Dashboard and Default. You have to manually remove these apps and then run

py4web setup apps

in order to re-install them. This is a safety precaution, in case you made changes to those apps.

If you installed py4web in any other way, you must upgrade it manually. First you have to make a backup of any personal py4web work you’ve done, then delete the old installation folder and re-install the framework again.

First run

Running py4web using any of the previous procedure should produce an output like this:


Generally apps is the name of the folder where you keep all your apps, and can be explicitly set wit the run command. (Yet nothing prevents you from grouping apps in multiple folders with different names.) If that folder does not exist, it is created. PY4WEB expects to find at least two apps in this folder: Dashboard (_dashboard) and Default (_default). If it does not find them, it installs them.

Dashboard is a web based IDE. It will be described in the next chapter.

Default is an app that does nothing other than welcome the user.


Some apps - like Dashboard and Default - have a special role in py4web and therefore their actual name starts with _ to avoid conflicts with apps created by you.

Once py4web is running you can access a specific app at the following urls:


In order to stop py4web, you need to hit Control-C on the window where you run it.


ONLY the Default app is special because if does not require the “{appname}/” prefix in the path, like all the other apps do. In general you may want to symlink apps/_default to your default app.

For all apps the trailing /index is also optional.


For Windows: it could be that Ctrl-C does not work in order to stop py4web. In this case, try with Ctrl-Break or Ctrl-Fn-Pause.

Command line options

py4web provides multiple command line options which can be listed by running it without any argument

# py4web

You can have additional help for a specific command line option by running it with the –help or -h argument.

call command option

# py4web call -h

  Call a function inside apps_folder

  -Y, --yes          No prompt, assume yes to questions  [default: False]
  --args TEXT        Arguments passed to the program/function  [default: {}]
  -help, -h, --help  Show this message and exit.

For example:

# py4web call apps examples.test.myfunction --args '{"x": 100}'

where myfunction is the function you want to call in apps/examples/ Note that you have to use the single and double quotes just as shown for parameters to work.

new_app command option

# py4web new_app -h

  Create a new app copying the scaffolding one

  -Y, --yes                No prompt, assume yes to questions  [default:

  -s, --scaffold_zip TEXT  Path to the zip with the scaffolding app
  -help, -h, --help        Show this message and exit.

This currently gives an error on binaries installations and from source installation (locally), because they miss the asset zip file.

run command option

# py4web run -h

  Run the applications on apps_folder

  -Y, --yes                     No prompt, assume yes to questions
                                [default: False]

  -H, --host TEXT               Host name  [default:]
  -P, --port INTEGER            Port number  [default: 8000]
  -A, --app_names TEXT          List of apps to run, comma separated (all if omitted or
  -p, --password_file TEXT      File for the encrypted password  [default:
  -Q, --quiet                   Suppress server output
  -R, --routes                  Write apps routes to file
  -s, --server                  [default|wsgiref|tornado|gunicorn|gevent|waitress|gunicorn|gunicornGevent|gevent|
                                Web server to use
  -w, --number_workers INTEGER  Number of workers  [default: 0]
  -d, --dashboard_mode TEXT     Dashboard mode: demo, readonly, full, none
                                [default: full]

  --watch [off|sync|lazy]       Watch python changes and reload apps
                                automatically, modes: off, sync, lazy
                                [default: lazy]

  --ssl_cert PATH               SSL certificate file for HTTPS
  --ssl_key PATH                SSL key file for HTTPS
  --errorlog TEXT               Where to send error logs
                                [default: :stderr]
  -L, --logging_level INTEGER   The log level (0 - 50) [default: 30
  -D, --debug                   Debug switch  [default: False]
  -U, --url_prefix TEXT         Prefix to add to all URLs in and out
  -help, -h, --help             Show this message and exit.

The app_names option lets you filter which specific apps you want to serve (comma separated). If absent or empty all the apps in the APPS_FOLDER will be run.

The url_prefix option is useful for routing at the py4web level. It allows mapping to multiple versions of py4web running on different ports as long as the url_prefix and port match the location. For example py4web run --url_prefix=/abracadabra --port 8000 apps.

By default py4web will automatically reload an application upon any changes to the python files of that application. The reloading will occur on any first incoming request to the application that has been changed (lazy-mode). If you prefer an immediate reloading (sync-mode), use py4web run --watch sync. For production servers, it’s better to use py4web run --watch off in order to avoid unneded checks (but you will need to restart py4web for activating any change).


The --watch directive looks for any changes occurring to the python files under the /apps folder only. Any modifications to the standard py4web programs will always require a full restart of the framework.

The default web server used is currently rocketServer, but you can change this behaviour with the server option. Rocket3 is the multi-threaded web server used by web2py stripped of all the Python2 logic and dependencies.

The logging_level values are defined in the logging standard python module. The default value is 30 (it corresponds to WARNING). Other common values are 0 (NOTSET), 10 (DEBUG), 20 (INFO), 40 (ERROR) and 50 (CRITICAL). Using them, you’re telling the library you want to handle all events from that level on up.

The debug parameter automatically sets logging_level to 0 and logs all calls to fixture functions. It also logs when a session is found, invalid, saved.

set_password command option

# py4web set_password -h
Usage: set_password [OPTIONS]

  Set administrator's password for the Dashboard

  --password TEXT           Password value (asked if missing)
  -p, --password_file TEXT  File for the encrypted password  [default:

  -h, -help, --help         Show this message and exit.

If the --dashboard_mode is not demo or none, every time py4web starts, it asks for a one-time password for you to access the dashboard. This is annoying. You can avoid it by storing a pdkdf2 hashed password in a file (by default called password.txt) with the command

py4web set_password

It will not ask again unless the file is deleted. You can also use a custom file name with

py4web set_password my_password_file.txt

and then ask py4web to re-use that password at runtime with

py4web run -p my_password_file.txt apps

Finally you can manually create the file yourself with:

python3 -c "from pydal.validators import CRYPT; open('password.txt','w').write(str(CRYPT()(input('password:'))[0]))"
password: *****

setup command option

# py4web setup -h

  Setup new apps folder or reinstall it

  -Y, --yes          No prompt, assume yes to questions  [default: False]
  -help, -h, --help  Show this message and exit.

This option create a new apps folder (or reinstall it). If needed, it will ask for the confirmation of the new folder’s creation and then for copying every standard py4web apps from the assets folder. It currently does nothing on binaries installations and from source installation (locally) - for them you can manually copy the existing apps folder to the new one.

shell command option

# py4web shell -h

  Open a python shell with apps_folder's parent added to the path

  -Y, --yes          No prompt, assume yes to questions  [default: False]
  -h, -help, --help  Show this message and exit.

Py4web’s shell is just the regular python shell with apps added to the search path. Notice that the shell is for all the apps, not a single one. You can then import the needed modules from the apps you need to access.

For example, inside a shell you can

from apps.myapp import db
from py4web import Session, Cache, Translator, DAL, Field
from py4web.utils.auth import Auth

version command option

# py4web version -h
Usage: version [OPTIONS]

  Show versions and exit

  -a, --all          List version of all modules
  -h, -help, --help  Show this message and exit.

With the -all option you’ll get the version of all the available python modules, too.

Special installations

There are special cases in which you cannot or don’t want to use one of the generic installation instructions we’ve already described. There is a special folder called deployment_tools in the py4web repository that collects some special recipes. They are briefly described here, along with some tips and tricks.


To use https with the build-in web server (Rocket3) these are the steps:

If you use VSCode to run py4web you may want to update the py4web launch.json file to contain:

"configurations": [
            "name": "py4web",
            "type": "python",
            "request": "launch",
            "program": "${workspaceFolder}/",
            "args": [
                "--ssl_cert", "/path_to/localhost.crt",
                "--ssl_key", "/path_to/localhost.key",
                "--server", "rocketServer",

Notice that /path_to/ should be the absolute path to the location of your certificate.


py4web is a standard WSGI application. So, if a full program installation it’s not feasible you can simply run py4web as a WSGI app. For example, using gunicorn-cli, create a python file:

from py4web.core import wsgi
application = wsgi(apps_folder="apps")

and then start the application using cli:

gunicorn -w 4 py4web_wsgi:application

The wsgi function takes arguments with the same name as the command line arguments.

Deployment on GCloud (aka GAE - Google App Engine)

Login into the Gcloud console and create a new project. You will obtain a project id that looks like “{project_name}-{number}”.

In your local file system make a new working folder and cd into it:

mkdir gae
cd gae

Copy the example files from py4web (assuming you have the source from github)

cp /path/to/py4web/development_tools/gcloud/* ./

Copy or symlink your apps folder into the gae folder, or maybe make a new apps folder containing an empty and symlink the individual apps you want to deploy. You should see the following files/folders:

  ... your apps ...

Install the Google SDK, py4web and setup the working folder:

make install-gcloud-linux
make setup
gcloud config set {your email}
gcloud config set {project id}

(replace {your email} with your google email account and {project id} with the project id obtained from Google).

Now every time you want to deploy your apps, simply do:

make deploy

You may want to customize the Makefile and app.yaml to suit your needs. You should not need to edit

Deployment on

Watch the YouTube video and follow the detailed tutorial . The script is in py4web/deployment_tools/

Deployment on Docker/Podman

On deployment_tools/docker there is a simple Dockerfile for quickly running a py4web container. There is also a docker-compose.yml file for setting up a more complex multi-container with PostgreSQL. A ready docker example based on the Scaffold application can be cloned from this repository <>

Note that you can use them also with Podman, which has the advantage of does not requiring sudo and does not running any background daemon.

Deployment on Ubuntu

On deployment_tools/ubuntu there is a bash script tested with Ubuntu Server 20.04.03 LTS. It uses nginx and self-signed certificates. It optionally manage iptables, too.