state_apply_action_with_legality_check.md

OpenSpiel state methods: apply_action_with_legality_check

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apply_action_with_legality_check(action: int)

Applies the specified action to the state, but first verifies that the action is legal. If the action is not in the list of legal actions, an error is raised. This is a safer (but slower) alternative to apply_action(), which skips legality checks for performance.

Examples:

import pyspiel

game = pyspiel.load_game("tic_tac_toe")
state = game.new_initial_state()

# Legal action: succeeds
state.apply_action_with_legality_check(4)  # Take center square

# Illegal action: raises an error (square already taken)
try:
    state.apply_action_with_legality_check(4)
except pyspiel.SpielError as e:
    print(e)  # Action is not legal