statemachine.py

A finite state machine specialized for regular-expression-based text filters, this module defines the following classes:

StateMachine, a state machine
State, a state superclass
StateMachineWS, a whitespace-sensitive version of StateMachine
StateWS, a state superclass for use with StateMachineWS
SearchStateMachine, uses re.search() instead of re.match()
SearchStateMachineWS, uses re.search() instead of re.match()
ViewList, extends standard Python lists.
StringList, string-specific ViewList.

Exception classes:

StateMachineError
UnknownStateError
DuplicateStateError
UnknownTransitionError
DuplicateTransitionError
TransitionPatternNotFound
TransitionMethodNotFound
UnexpectedIndentationError
TransitionCorrection: Raised to switch to another transition.
StateCorrection: Raised to switch to another state & transition.

Functions:

string2lines(): split a multi-line string into a list of one-line strings

How To Use This Module

(See the individual classes, methods, and attributes for details.)

Import it: import statemachine or from statemachine import .... You will also need to import re.
Derive a subclass of State (or StateWS) for each state in your state machine:
```
class MyState(statemachine.State):
```
Within the state's class definition:
1. Include a pattern for each transition, in State.patterns:
```
patterns = {'atransition': r'pattern', ...}
```
2. Include a list of initial transitions to be set up automatically, in State.initial_transitions:
```
initial_transitions = ['atransition', ...]
```
3. Define a method for each transition, with the same name as the transition pattern:
```
def atransition(self, match, context, next_state):
    # do something
    result = [...]  # a list
    return context, next_state, result
    # context, next_state may be altered
```
  Transition methods may raise an EOFError to cut processing short.
4. You may wish to override the State.bof() and/or State.eof() implicit transition methods, which handle the beginning- and end-of-file.
5. In order to handle nested processing, you may wish to override the attributes State.nested_sm and/or State.nested_sm_kwargs.
  
  If you are using StateWS as a base class, in order to handle nested indented blocks, you may wish to:
  - override the attributes StateWS.indent_sm, StateWS.indent_sm_kwargs, StateWS.known_indent_sm, and/or StateWS.known_indent_sm_kwargs;
  - override the StateWS.blank() method; and/or
  - override or extend the StateWS.indent(), StateWS.known_indent(), and/or StateWS.firstknown_indent() methods.

Create a state machine object:

sm = StateMachine(state_classes=[MyState, ...],
                  initial_state='MyState')

Obtain the input text, which needs to be converted into a tab-free list of one-line strings. For example, to read text from a file called 'inputfile':
```
input_string = open('inputfile').read()
input_lines = statemachine.string2lines(input_string)
```
Run the state machine on the input text and collect the results, a list:
```
results = sm.run(input_lines)
```
Remove any lingering circular references:
```
sm.unlink()
```

Zyrianes / _(sandbox)

rst doc

statemachine.py

How To Use This Module