1. Introduction

1.1. Functionality

Pywbem supports the following functionality:

  • WBEM client library API

    This API supports issuing WBEM operations to a WBEM server, using the CIM operations over HTTP (CIM-XML) protocol defined in the DMTF standards DSP0200 and DSP0201.

  • WBEM server API

    This API encapsulates certain functionality of a WBEM server for use by a WBEM client application, such as determining the Interop namespace of the server, or the management profiles advertised by the server.

  • WBEM indication API

    This API supports starting and stopping a WBEM listener that waits for indications (i.e. events) emitted by a WBEM server using the CIM-XML protocol. The API also supports managing subscriptions for such indications.

  • MOF compiler API

    This API provides for invoking the MOF compiler and for plugging in your own CIM repository into the MOF compiler.

  • WBEM utility commands

    Pywbem includes a few utility commands:

    • mof_compiler

      A MOF compiler that takes MOF files as input and creates, updates or removes CIM instances, classes or qualifier types in a CIM repository.

      See DSP0004 for a description of MOF (Managed Object Format).

      By default, the CIM repository used by the MOF compiler is in a WBEM server. The MOF compiler API provides for plugging in your own CIM repository the compiler can work against.

    • wbemcli

      A WBEM command line interface that provides an interactive Python environment for issuing WBEM operations to a WBEM server.

1.2. Installation

Pywbem is a pure Python package that can be installed from PyPi or from its repository by the usual means for installing Python packages.

Some of the Python packages used by pywbem have dependencies on operating system packages. As of pywbem v0.8, the setup script has support for installing prerequisite operating system packages via a new install_os command for the setup script. Alternatively, you can establish these prerequisites yourself. For details, see Prerequisite operating system packages.

The following examples show different ways to install pywbem. They all ensure that prerequisite Python packages are installed as needed:

  1. Install the latest released version, assuming the OS-level prerequisites are already established:

    $ pip install pywbem
    
  2. Install the latest released version and also install (or display) any OS-level prerequisites:

    $ pip download --no-deps --no-binary :all: pywbem
    $ tar -xzf pywbem-*.tar.gz
    

    or, when using pip versions before 8.0.0, you have to know the pywbem version to download:

    $ curl -L https://github.com/pywbem/pywbem/archive/v0.9.0.tar.gz |tar -xz
    

    Followed in both cases by these commands:

    $ cd pywbem-*
    $ python setup.py install_os install
    
  3. Install a particular branch from the Git repository:

    $ pip install git+https://github.com/pywbem/pywbem.git@<branch-name>
    

These examples install pywbem and its prerequisite Python packages into the currently active Python environment. By default, the system Python environment is active. This is probably the right choice if you just want to use the scripts that come with pywbem. In that case, you need to prepend the installation commands shown above (i.e. pip and python setup.py) with sudo, and your Linux userid needs to be authorized accordingly. If your intention is to write code against the pywbem APIs, installation into a virtual Python environment is recommended).

The second example installs the OS-level prerequisites always into the system, regardless of whether or not you have a virtual Python environment active. The setup script uses sudo under the covers. This means that you don’t need to take care about that and can use sudo to control whether you install the Python packages into a virtual or system Python environment.

The command syntax above is shown for Linux, but works in similar ways on Windows and OS-X.

In case of trouble with the installation, see the Troubleshooting section.

You can verify that pywbem and its dependent packages are installed correctly by importing the package into Python:

$ python -c "import pywbem; print('ok')"
ok

1.3. Prerequisite operating system packages

Prerequisite operating system packages can be installed by the pywbem setup script using a new command install_os:

$ python setup.py install_os

For a number of well-known Linux distributions, the setup script will install the packages using the respective installer program (e.g. yum on RHEL). For other Linux distributions and for non-Linux operating systems, the setup script will display the package names that would be needed on RHEL, leaving it to the user to translate them accordingly.

When installing such packages on Linux, the setup script uses the sudo command, so your userid needs to be authorized accordingly.

This command also downbloads and builds swig and installs its build prerequisites if it cannot be installed as an operating system package in the required version.

The second example in the previous section shows how to use the new setup command install_os. It is really simple to be used and avoids the manual procedure for establishing the operating system packages as described in the remainder of this section.

For manual installation of the prerequisite operating system packages, or for including pywbem in distributions, the following table lists the packages and their version requirements for a number of Linux distributions:

Distributions Package name Version requirements
RedHat, CentOS, Fedora openssl-devel >=1.0.1
gcc-c++ >=4.4
python-devel for Python 2.6, 2.7
python3{N}u-devel for Python 3.{N} from IUS community (python3{N}u)
python3{N}-devel for Python 3.{N} not from IUS (python3{N})
swig >=2.0
Ubuntu, Debian, LinuxMint libssl-dev >=1.0.1
g++ >=4.4
python-dev for Python 2.6, 2.7
python3-dev for Python 3.4 - 3.6
swig >=2.0
SLES, OpenSUSE openssl-devel >=1.0.1
gcc-c++ >=4.4
python-devel for Python 2.6, 2.7
python3-devel for Python 3.4 - 3.6
swig >=2.0

On some distributions, the swig package is not available in the required version. In such cases, it can be built from its sources, as follows:

  1. Install the pcre-devel package (RedHat etc. and SLES etc.) or the libpcre3 and libpcre3-dev packages (Ubuntu etc.).

  2. Download the swig source archive and unpack it:

    $ wget -q -O swig-2.0.12.tar.gz http://sourceforge.net/projects/swig/files/swig/swig-2.0.12/swig-2.0.12.tar.gz/download
    $ tar -xf swig-2.0.12.tar.gz
    
  3. Configure and build it:

    $ cd swig-2.0.12
    $ ./configure --prefix=/usr
    $ make swig
    
  4. Install it:

    $ sudo make install
    
  5. Verify its version:

    $ swig -version
    SWIG Version 2.0.12
    

1.4. Package version

The version of the pywbem package can be accessed by programs using the pywbem.__version__ variable:

pywbem._version.__version__ = '0.11.0.dev0'

Version of the pywbem package, as a string.

Possible formats for the version string are:

  • “M.N.U.dev0”: During development of future M.N.U release (not released to PyPI)
  • “M.N.U.rcX”: Release candidate X of future M.N.U release (not released to PyPI)
  • “M.N.U”: The final M.N.U release

Note: For tooling reasons, the variable is shown as pywbem._version.__version__, but it should be used as pywbem.__version__.

1.5. Supported environments

Pywbem is supported in these environments:

  • Operating Systems: Linux, Windows, OS-X
  • Python: 2.6, 2.7, 3.4, 3.5, 3.6

Limitations:

  • On Windows, pywbem is not supported on Python 2.6, because M2Crypto in the M2CryptoWin32/64 package does not support Python 2.6.
  • On Windows, pywbem has not been tested on 64-bit versions of Python, because the libxslt etc. development packages needed to install lxml that are used do not provide the link libraries in the format needed by lxml. Because lxml is only used for development and test of pywbem, just running pywbem on 64-bit versions of Windows may or may not work.

1.6. Standards conformance

Pywbem conforms to the following CIM and WBEM standards, in the version specified when following the links to the standards:

1.7. Deprecation policy

Since its v0.7.0, Pywbem attempts to be as backwards compatible as possible.

However, in an attempt to clean up some of its history, and in order to prepare for future additions, the Python namespaces visible to users of pywbem need to be cleaned up.

Also, occasionally functionality needs to be retired, because it is flawed and a better but incompatible replacement has emerged.

In pywbem, such changes are done by deprecating existing functionality, without removing it. The deprecated functionality is still supported throughout new minor releases. Eventually, a new major release will break compatibility and will remove the deprecated functionality.

In order to prepare users of pywbem for that, deprecation of functionality is stated in the API documentation, and is made visible at runtime by issuing Python warnings of type DeprecationWarning (see the Python warnings module).

Since Python 2.7, DeprecationWarning messages are suppressed by default. They can be shown for example in any of these ways:

  • By specifying the Python command line option: -W default
  • By invoking Python with the environment variable: PYTHONWARNINGS=default

It is recommended that users of the pywbem package run their test code with DeprecationWarning messages being shown, so they become aware of any use of deprecated functionality.

Here is a summary of the deprecation and compatibility policy used by pywbem, by release type:

  • New update release (M.N.U -> M.N.U+1): No new deprecations; fully backwards compatible.
  • New minor release (M.N.U -> M.N+1.0): New deprecations may be added; as backwards compatible as possible.
  • New major release (M.N.U -> M+1.0.0): Deprecated functionality may get removed; backwards compatibility may be broken.

Compatibility is always seen from the perspective of the user of pywbem, so a backwards compatible new pywbem release means that the user can safely upgrade to that new release without encountering compatibility issues.

1.8. Python namespaces

The external APIs of pywbem are defined by the symbols in the pywbem namespace. That is the only Python namespace that needs to be imported by users.

With pywbem versions prior to v0.8, it was common for users to import the sub-modules of pywbem (e.g. pywbem.cim_obj). The sub-modules that existed prior to v0.8 are still available for compatibility reasons. Starting with v0.8, the pywbem namespace was cleaned up, and not all public symbols available in the sub-module namespaces are available in the pywbem namespace anymore. The symbols in the sub-module namespaces are still available for compatibility, including those that are no longer available in the pywbem namespace. However, any use of symbols from the sub-module namespaces is deprecated starting with v0.8, and you should assume that a future version of pywbem will remove them. If you miss any symbol you were used to use, please open an issue.

New sub-modules added since pywbem v0.8 have a leading underscore in their name in order to document that they are considered an implementation detail and that they should not be imported by users.

With pywbem versions prior to v0.11, the MOF compiler API was only available in the pywbem.mof_compiler namespace. Starting with pywbem version v0.11, it is also available in the pywbem namespace and should be used from there.

This documentation describes only the external APIs of pywbem, and omits any internal symbols and any sub-modules.

1.9. Configuration variables

Pywbem supports a very limited number of configuration variables that influence certain specific behavior.

These configuration variables are read by pywbem only after its modules have been loaded, so they can be modified by the user directly after importing pywbem. For example:

import pywbem
pywbem.ENFORCE_INTEGER_RANGE = False

Note that the pywbem source file defining these variables should not be changed by the user. Instead, the technique shown in the example above should be used to modify the configuration variables.

Note: Due to limitations of the documentatin tooling, the following configuration variables are shown in the pywbem.config namespace. However, they should be used from the pywbem namespace.

pywbem.config.ENFORCE_INTEGER_RANGE = True

Enforce the allowable value range for CIM integer types (e.g. Uint8). For details, see the CIMInt base class.

  • True (default): Pywbem enforces the allowable value range; Assigning values out of range causes ValueError to be raised.
  • False: Pywbem does not enforce the allowable value range; Assigning values out of range works in pywbem. Note that a WBEM server may or may not reject such out-of-range values.
pywbem.config.DEFAULT_ITER_MAXOBJECTCOUNT = 1000

Default setting for the MaxObjectCount attribute for all of the WBEMConnection:Iter... operations. If this attribute is not specified on a request such as IterEnumerateInstance this value will be used as the value for MaxObjectCount. Note that this does not necessarily optimize the performance of these operations.