Upgrading¶

Deprecated: cement.core.interface.list()¶

This function should no longer be used in favor of CementApp.handler.list_types(). It will continue to work throughout Cement 2.x, however is not compatible if CementApp.Meta.use_backend_globals == False.

Related:

• Issue #366
• Issue #376

TypeError: my_signal_hook() takes exactly 2 arguments (3 given)¶

In Cement 2.6, functions registered to the signal hook were only expected/required to accept the signum and frame arguments, however signal hook functions must now also accept the app object as an argument as well.

After upgrading to Cement 2.8, you might receive something similar to the following exception:

TypeError: my_signal_hook() takes exactly 2 arguments (3 given)

The fix is to simply prefix any signal hook functions with an app argument.

For example:

def my_signal_hook(signum, frame):
    pass

Would need to be:

def my_signal_hook(app, signum, frame):
    pass

Related:

• Issue #311

TypeError: render() got an unexpected keyword argument¶

In Cement 2.6, output handlers were not required to accept **kwargs, however this is now required to allow applications to mix different types of output handlers together that might support different features/usage.

After upgrading to Cement 2.8, you might receive something similar to the following exception:

TypeError: render() got an unexpected keyword argument

This would most likely be the case because you have created your own custom output handler, or are using a third-party output handler that has not been updated to support Cement 2.8 yet. The fix is to simply add **kwargs to the end of the render() method.

For example:

def render(self, data):
    pass

Would need to be:

def render(self, data, **kwargs):
    pass

CementApp.Meta.exit_on_close Defaults to False¶

In Cement 2.6, the feature to call sys.exit() when app.close() is called was implemented, however defaulting it to True is not the ideal behavior. The default is now False, making it the developers option to explicitly enable it.

To revert the change, and default exit_on_close to True, simply set it in CementApp.Meta.exit_on_close:

from cement.core.foundation import CementApp

class MyApp(CementApp):
    class Meta:
        label = 'myapp'
        exit_on_close = True

InterfaceError: Invalid handler ... missing ‘_meta.label’.¶

Prior to Cement 2.5.2, CementBaseController.Meta.label defaulted to base. The new default is None, causing the potential for breakage of a controller that did not explicity set the label meta option.

You can resolve this error by explicity setting the label meta option:

class MyBaseController(CementBaseController):
    class Meta:
        label = 'base'

CementApp.render() Prints Output Without Calling print()¶

Before Cement 2.3.2 the app.render() function did not actually print anything, therefore you would have to call print app.render(). This now defaults to writing output to sys.stdout, but can be modified for the older behavior by passing out=None when calling it:

app.render(data, out=None)

Additionally, you can also now write directly to a file:

myfile = open('/path/to/myfile', 'w')
app.render(data, out=myfile)
myfile.close()

error: unrecognized arguments: –json/–yaml¶

After upgrading to Cement > 2.3.2 you might encounter the error:

error: unrecognized arguments: --json

Or similar errors like:

error: unrecognized arguments: --yaml

This is due to a design change, and a new feature allowing the end user to optionally override handlers via command line. Rather than having a unique option for every type of output handler, you now have one option that allows overriding the defined output handler by passing it the handler label.

Note that only handlers that have overridable = True in their meta-data will be valid options.

To resolve this issue, you simply need to pass -o json or -o yaml at command line to override the default output handler.

Related:

• Issue #229

NoSectionError: No section: ‘log’¶

After upgrading to Cement > 2.3.2 you might encounter the error:

NoSectionError: No section: 'log'

In previous versions of Cement < 2.3.2, the default logging configuration section in the config file was [log]. This has been changed to [log.logging] in order to be consistent with all other handler configuration sections.

Another issue you might encounter due to the above change is that log related configuration settings read from a configuration file would no longer work. The necessary change to resolve this issue is to change all references of log in relation to the log configuration section, to log.logging.

Related:

• Issue #227

TypeError: load() takes no arguments (1 given)¶

After upgrading to Cement > 2.3.2 you might encounter the error:

TypeError: load() takes no arguments (1 given)

Previous versions of Cement < 2.3.2 did not require an app argument to be passed to the load() functions of extensions/plugins/bootstrap modules. In Cement > 2.3.2 all extension/plugins/bootstrap modules must accept a single argument named app which is the application object in its current state when load() is called.

To resolve this issue simply modify all relevant load() functions to accept the app argument. For example:

def load():
    pass

To:

def load(app):
    pass

ImportError: cannot import name version¶

When attempting to install Cement > 2.1 on a system that already has an older version of Cement < 2.1 you will likely run into this error:

ImportError: cannot import name version

Currently we do not have a way to resolve this programatically in Cement. The resolution is to remove the older version of Cement < 2.1, and then re-install the newer version.

Related:

• Issue #237

FrameworkError: Duplicate Arguments/Commands¶

After upgrading, you might encounter one or both of the following errors related to application controllers:

cement.core.exc.FrameworkError: Duplicate command named 'mycommand' found
in controller '<__main__.MySecondController object at 0x10669ab50>'

cement.core.exc.FrameworkError: argument -f/--foo: conflicting option
string(s): -f, --foo

This is likely due to a change in how application controllers are configured. By default, all controllers are of type embedded, meaning that their arguments and commands are added to the parent controller. To resolve this issue you can change the stacked_type to nested, meaning that the stacked controller will be an additional sub-command under the parent (nesting a new level commands/arguments).

For example:

class MyStackedController(CementBaseController):
    class Meta:
        label = 'my_stacked_controller'
        stacked_on = 'base'
        stacked_type = 'nested'

Related:

• Issue #234

Discontinued use of Setuptools Namespace Packages¶

Previous versions of Cement utilitized Setuptools namespace packages in order to allow external libraries (such as optional framework extensions) to use the cement.ext namespace. Meaning that an extension packaged separately could use the namespace cement.ext.ext_myextension and be imported from the cement.ext namespace as if it were shipped with the mainline sources directly. This indirectly caused issues with certain IDE’s due to the fact that namespace packages do not install a proper __init__.py and are handled differently by Setuptools.

With the move to merging optional extenions into mainline sources, we no longer require the use of Setuptools namespace packages. That said, if a developer had created their own extension using the cement.ext namespace, that extension would no longer work or worse may confusing Python into attempting to load cement.ext from the extension and not Cement causing even bigger problems.

To resolve this issue, simply change the extension module to anything other than cement.ext, such as myapp.ext.

Related:

• Issue #202

LoggingLogHandler Changes¶

The clear_loggers meta option is now a list, rather than a boolean. Therefore, rather than telling LoggingLogHandler to ‘clear all previously defined loggers’, you are telling it to ‘clear only these previously defined loggers’ in the list.

If your application utilizied the LoggingLogHandler.Meta.clear_loggers option, you would simply need to change it from a boolean to a list of loggers such as ['myapp', 'some_other_logging_namespace'].

Related:

• Issue #163

ConfigParserConfigHandler Changes¶

The ConfigParserConfigHandler.has_key() function has been removed. To update your application for these changes, you would look for all code similar to the following:

if myapp.config.has_key('mysection', 'mykey'):
    # ...

And modify it to something similar to:

if 'mykey' in myapp.config.keys('mysection'):
    # ...

Related:

• Issue #173

CementApp Changes¶

The CementApp.get_last_rendered() function has been deprected. Developers should now use the CementApp.last_rendered property instead. To update your application for these changes, you would look for all code similar to:

CementApp.get_last_rendered()

And modify it to something similar to:

CementApp.last_rendered

Related:

• Issue #201 - Add Deprecation Warning for CementApp.get_last_rendered()

CementBaseController Changes¶

All short-cuts such as log, pargs, etc have been removed from CementBaseController due to the fact that these class members could clash if the developer added a command/function of the same name. To update your application for these changes, in any classes that subclass from CementBaseController, you might need to modify references to self.log, self.pargs, etc to self.app.log, self.app.pargs, etc.

Additionally, if you wish to re-implement these or other shortcuts, you can do so by overriding _setup() in your controller code, and add something similar to the following:

def _setup(self, *args, **kw):
    res = super(MyClass, self)._setup(*args, **kw)
    self.log = self.app.log
    self.pargs = self.app.pargs
    # etc

    return res

An additional change to CementBaseController is that the application’s base controller attached to YourApp.Meta.base_controller now must have a label of base. Previously, the base controller could have any label however this is now a hard requirement. To update your application for these changes, simply change the label of your base controller to base.

Finally, the CementBaseController used to have members called hidden, visible, and exposed which were each a list of controller functions used for handling dispatch of commands, and how they are displayed in --help. These members no longer exist.

These members were never documented, and is very unlikely that anybody has ever used them directly. Updating your application for these changes would be outside the scope of this document.

Related:

• Issue #141
• Issue #167
• Issue #179

Backend Changes¶

Several backend pieces have been moved or renamed. For example cement.core.backend.handlers is now cement.core.backend.__handlers__, etc. The same goes for cement.core.backend.SAVED_STDOUT which is now cement.core.backend.__saved_stdout__. These are undocumented, and used specifically by Cement. It is unlikely that anyone has used these members directly, and updating your application for these changes is outside the scope of this document. See cement.core.backend to assess what, if any, change you may need to change in your code to compensate for these changes.

The cement.core.backend.defaults() function has moved to cement.utils.misc.init_defaults(). It’s usage is exactly the same.

The cement.core.backend.minimal_logger() function has moved to cement.utils.misc.minimal_logger. It’s usage is also the same.

Related:

• Issue #177
• Issue #178