Dp State

In this tutorial, you'll learn about How to Fix State Errors. We cover key concepts, practical examples, and best practices.

Fix state errors when state transitions managed by if/else causing cyclic complexity.

Quick Fix

Wrong

class Document:
    def publish(self):
        if self.state=='draft':
            self.state='moderation'
        elif self.state=='moderation':
            if self.admin: self.state='published'
        elif self.state=='published':
            pass  # no-op

State transition logic grows with each new state. Hard to maintain, easy to introduce bugs.

Right

from abc import ABC,abstractmethod
class State(ABC):
    @abstractmethod
    def publish(self,doc): pass
class Draft(State):
    def publish(self,doc): doc.state=Moderation()
class Moderation(State):
    def publish(self,doc):
        if doc.admin: doc.state=Published()
class Published(State):
    def publish(self,doc): pass
class Document:
    def __init__(self): self.state=Draft()
    def publish(self): self.state.publish(self)
d=Document(); d.publish()  # draft->moderation

Each state in own class. Transitions explicit. Adding new state doesn't change existing states.

Prevention

State pattern puts each state's behavior in separate class. Eliminates if/else chains.

DodaTech Tools

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