Use venv module rather than virtualenv

- simpler to use
- lighter dependency (or no dependency at all, depending on python distribution)
- retrocompatible

virtualenv package from pip to acheive virtual environment feature is no longer
needed, except for projects which need to support py2, which is no longer our
case.

Also, reword "virtualenv" to "virtual environment" in doc, to avoid confusion
with pip package name.

Ref #483

Makefile

@@ -1,4 +1,4 @@
-VIRTUALENV = virtualenv --python=python3
+VIRTUALENV = python3 -m venv
 SPHINX_BUILDDIR = docs/_build
 VENV := $(shell realpath $${VIRTUAL_ENV-.venv})
 PYTHON = $(VENV)/bin/python3

docs/contributing.rst

@@ -67,7 +67,7 @@ If System :ref:`installation-requirements` are fulfilled, you can just issue::
 
     make serve
 
-It will setup a `virtualenv <https://pypi.python.org/pypi/virtualenv>`_,
+It will setup a `Virtual environment <https://docs.python.org/3/tutorial/venv.html>`_,
 install dependencies, and run the test server.
 
 The hard way
@@ -193,7 +193,7 @@ The documentation is using `sphinx <http://www.sphinx-doc.org/en/stable/>`_ and
 its source is located inside the `docs folder
 <https://github.com/spiral-project/ihatemoney/tree/master/docs>`_.
 
-Install doc dependencies (within the virtualenv, if any)::
+Install doc dependencies (within the virtual environment, if any)::
 
   pip install -r docs/requirements.txt
 

docs/installation.rst

@@ -21,9 +21,9 @@ Requirements
 
 * **Python**: either 3.6, 3.7 or 3.8 will work.
 * **A Backend**: to choose among MySQL, PostgreSQL, SQLite or Memory.
-* **Virtualenv** (recommended): `virtualenv` package under Debian/Ubuntu.
+* **Virtual environment** (recommended): `python3-venv` package under Debian/Ubuntu.
 
-We recommend to use `virtualenv <https://pypi.python.org/pypi/virtualenv>`_ but
+We recommend to use `virtual environment <https://docs.python.org/3/tutorial/venv.html>`_ but
 it will work without if you prefer.
 
 If wondering about the backend, SQLite is the simplest and will work fine for
@@ -33,16 +33,16 @@ most small to medium setups.
 
 .. _virtualenv-preparation:
 
-Prepare virtualenv (recommended)
-================================
+Prepare virtual environment (recommended)
+=========================================
 
 Choose an installation path, here `/home/john/ihatemoney`.
 
-Create a virtualenv::
+Create a virtual environment::
 
-    virtualenv  -p /usr/bin/python3 /home/john/ihatemoney
+    python3 -m venv /home/john/ihatemoney
 
-Activate the virtualenv::
+Activate the virtual environment::
 
     source /home/john/ihatemoney/bin/activate
 
@@ -74,7 +74,7 @@ Configure database with MySQL/MariaDB (optional)
 
     apt install python3-dev libssl-dev
 
-2. Install PyMySQL (within your virtualenv)::
+2. Install PyMySQL (within your virtual environment)::
 
     pip install 'PyMySQL>=0.9,<0.10'
 
@@ -87,7 +87,7 @@ Configure database with PostgreSQL (optional)
 
 .. note:: Only required if you use Postgresql.
 
-1. Install python driver for PostgreSQL (from within your virtualenv)::
+1. Install python driver for PostgreSQL (from within your virtual environment)::
 
     pip install psycopg2
 

docs/upgrade.rst

@@ -15,7 +15,7 @@ General procedure
 
 *(sufficient for minor/patch upgrades)*
 
-1. From the virtualenv (if any)::
+1. From the virtual environment (if any)::
 
     pip install -U ihatemoney
 
@@ -47,7 +47,7 @@ Switch to a supported version of Python
 If you were running IHateMoney using Python < 3.6, you must, **before** upgrading:
 
 1. Ensure to have a Python ≥ 3.6 available on your system
-2. Rebuild your virtualenv (if any). It will *not* alter your database nor configuration. For example, if your virtualenv is in `/home/john/ihatemoney/`::
+2. Rebuild your virtual environment (if any). It will *not* alter your database nor configuration. For example, if your virtual environment is in `/home/john/ihatemoney/`::
 
      rm -rf /home/john/ihatemoney
      pyhton3 -m venv /home/john/ihatemoney
@@ -89,7 +89,7 @@ development only.
 1. Delete the cloned folder
 
 
-.. note:: If you are using a virtualenv, then the following commands should be run inside it (see
+.. note:: If you are using a virtual environment, then the following commands should be run inside it (see
           :ref:`virtualenv-preparation`).