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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def instantiate_labels(instructions):
 """ Takes an iterable of instructions which may contain label placeholders and assigns them all defined values. :return: list of instructions with all label placeholders assigned to real labels. """

    label_i = 1
    result = []
    label_mapping = dict()
    for instr in instructions:
        if isinstance(instr, Jump) and isinstance(instr.target, LabelPlaceholder):
            new_target, label_mapping, label_i = _get_label(instr.target, label_mapping, label_i)
            result.append(Jump(new_target))
        elif isinstance(instr, JumpConditional) and isinstance(instr.target, LabelPlaceholder):
            new_target, label_mapping, label_i = _get_label(instr.target, label_mapping, label_i)
            cls = instr.__class__  # Make the correct subclass
            result.append(cls(new_target, instr.condition))
        elif isinstance(instr, JumpTarget) and isinstance(instr.label, LabelPlaceholder):
            new_label, label_mapping, label_i = _get_label(instr.label, label_mapping, label_i)
            result.append(JumpTarget(new_label))
        else:
            result.append(instr)

    return result