在没有库的python中查找x给定y的函数

def find_x_without_library(y, data):
    for item in data:
        if item == y:
            return item
    return None

def find_x_without_library(y, data):
    for key, value in data.items():
        if value == y:
            return key
    return None

class CustomDataStructure:
    def __init__(self):
        self.data = []

    def add_pair(self, x, y):
        self.data.append((x, y))

    def find_x(self, y):
        for pair in self.data:
            if pair[1] == y:
                return pair[0]
        return None

# 示例用法
custom_data = CustomDataStructure()
custom_data.add_pair("x1", "y1")
custom_data.add_pair("x2", "y2")
custom_data.add_pair("x3", "y3")

result = custom_data.find_x("y2")
print(result)  # 输出：x2