69 lines
2.4 KiB
ReStructuredText
69 lines
2.4 KiB
ReStructuredText
.. _pb-py-compat:
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Python Version and Templating
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=============================
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Jinja2 templates leverage Python data types and standard functions. This
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makes for a rich set of operations that can be performed on data. However,
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this also means that certain specifics of the underlying Python becomes
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visible to template authors. Since Ansible playbooks use Jinja2 for templates
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and variables, this means that playbook authors need to be aware of these
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specifics as well.
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Unless otherwise noted, these differences are only of interest when running
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Ansible in Python2 versus Python3. Changes within Python2 and Python3 are
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generally small enough that they are not visible at the jinja2 level.
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.. _pb-py-compat-dict-views:
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Dictionary Views
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----------------
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In Python2, the :meth:`dict.keys`, :meth:`dict.values`, and :meth:`dict.items`
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methods returns a list. Jinja2 returns that to Ansible via a string
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representation that Ansible can turn back into a list. In Python3, those
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methods return a :ref:`dictionary view <python3:dict-views>` object. The
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string representation that Jinja2 returns for dictionary views cannot be parsed back
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into a list by Ansible. It is, however, easy to make this portable by
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using the :func:`list <jinja2:list>` filter whenever using :meth:`dict.keys`,
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:meth:`dict.values`, or :meth:`dict.items`::
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vars:
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hosts:
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testhost1: 127.0.0.2
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testhost2: 127.0.0.3
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tasks:
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- debug:
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msg: '{{ item }}'
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# Only works with Python 2
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#with_items: "{{ hosts.keys() }}"
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# Works with both Python 2 and Python 3
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with_items: "{{ hosts.keys() | list }}"
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.. _pb-py-compat-iteritems:
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dict.iteritems()
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----------------
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In Python2, dictionaries have :meth:`~dict.iterkeys`,
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:meth:`~dict.itervalues`, and :meth:`~dict.iteritems` methods. These methods
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have been removed in Python3. Playbooks and Jinja2 templates should use
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:meth:`dict.keys`, :meth:`dict.values`, and :meth:`dict.items` in order to be
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compatible with both Python2 and Python3::
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vars:
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hosts:
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testhost1: 127.0.0.2
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testhost2: 127.0.0.3
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tasks:
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- debug:
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msg: '{{ item }}'
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# Only works with Python 2
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#with_items: "{{ hosts.iteritems() }}"
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# Works with both Python 2 and Python 3
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with_items: "{{ hosts.items() | list }}"
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.. seealso::
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* The :ref:`pb-py-compat-dict-views` entry for information on
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why the :func:`list filter <jinja2:list>` is necessary
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here.
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