twisted.python.hook

Package twisted :: Package python :: Module hook |
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## Module twisted.python.hook

I define support for hookable instance methods.

These are methods which you can register pre-call and post-call external functions to augment their functionality. People familiar with more esoteric languages may think of these as "method combinations".

This could be used to add optional preconditions, user-extensible callbacks (a-la emacs) or a thread-safety mechanism.

The four exported calls are:

- `addPre`
- `addPost`
- `removePre`
- `removePost`

All have the signature (class, methodName, callable), and the callable they take must always have the signature (instance, *args, **kw) unless the particular signature of the method they hook is known.

Hooks should typically not throw exceptions, however, no effort will be made by this module to prevent them from doing so. Pre-hooks will always be called, but post-hooks will only be called if the pre-hooks do not raise any exceptions (they will still be called if the main method raises an exception). The return values and exception status of the main method will be propogated (assuming none of the hooks raise an exception). Hooks will be executed in the order in which they are added.

Exceptions
`HookError` | An error which will fire when an invariant is violated.

Function Summary
| ``_addHook`(klass, name, phase, func)` (private) adds a hook to a method on a class
| ``_dehook`(klass, name)` (private) causes a certain method name no longer to be hooked on a class
| ``_enhook`(klass, name)` (private) causes a certain method name to be hooked on a class
| ``_removeHook`(klass, name, phase, func)` (private) removes a hook from a method on a class
| ``_XXX`(k, n, s)` string manipulation garbage
| ``addPost`(klass, name, func)` hook.addPost(klass, name, func) -> None
| ``addPre`(klass, name, func)` hook.addPre(klass, name, func) -> None
| ``ORIG`(k, n)` (private) munging to turn a method name into an `original' identifier
| ``POST`(k, n)` (private) munging to turn a method name into a post-hook-method-name
| ``PRE`(k, n)` (private) munging to turn a method name into a pre-hook-method-name
| ``removePost`(klass, name, func)` hook.removePre(klass, name, func) -> None
| ``removePre`(klass, name, func)` hook.removePre(klass, name, func) -> None

Variable Summary
`str` | `_ORIG` = `'__hook_orig_%s_%s_%s__'`
`str` | `_POST` = `'__hook_post_%s_%s_%s__'`
`str` | `_PRE` = `'__hook_pre_%s_%s_%s__'`
`str` | `hooked_func` = `'\n\nimport %(module)s\n\ndef %(name)s(*ar...`

Function Details

### _addHook(klass, name, phase, func) (private) adds a hook to a method on a class

### _dehook(klass, name) (private) causes a certain method name no longer to be hooked on a class

### _enhook(klass, name) (private) causes a certain method name to be hooked on a class

### _removeHook(klass, name, phase, func) (private) removes a hook from a method on a class

### _XXX(k, n, s) string manipulation garbage

### addPost(klass, name, func) hook.addPost(klass, name, func) -> None Add a function to be called before the method klass.name is invoked.

### addPre(klass, name, func) hook.addPre(klass, name, func) -> None Add a function to be called before the method klass.name is invoked.

### ORIG(k, n) (private) munging to turn a method name into an `original' identifier

### POST(k, n) (private) munging to turn a method name into a post-hook-method-name

### PRE(k, n) (private) munging to turn a method name into a pre-hook-method-name

### removePost(klass, name, func) hook.removePre(klass, name, func) -> None Remove a function (previously registered with addPost) so that it is no longer executed after klass.name.

### removePre(klass, name, func) hook.removePre(klass, name, func) -> None Remove a function (previously registered with addPre) so that it is no longer executed before klass.name.

Variable Details

    ### _ORIG Type: `str` Value:
        '__hook_orig_%s_%s_%s__'

    ### _POST Type: `str` Value:
        '__hook_post_%s_%s_%s__'

    ### _PRE Type: `str` Value:
        '__hook_pre_%s_%s_%s__'

    ### hooked_func Type: `str` Value:
        '''

        import %(module)s

        def %(name)s(*args, **kw):
            klazz = %(module)s.%(klass)s
            for preMethod in klazz.%(preName)s:
                preMethod(*args, **kw)
        ...

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