Python字典遍历修改键的避坑实战案例

def remove_odd_key():
    data = {1: "苹果", 2: "香蕉", 3: "橙子", 4: "葡萄"}
    # 直接遍历字典键并删除
    for k in data.keys():
        if k % 2 != 0:
            del data[k]
    print(data)

if __name__ == "__main__":
    remove_odd_key()

RuntimeError: dictionary changed size during iteration

def add_new_key():
    data = {"a": 10, "b": 20}
    for k in data.keys():
        new_k = k + "_new"
        data[new_k] = data[k] * 2
    print(data)

if __name__ == "__main__":
    add_new_key()

def fix_remove_by_copy():
    data = {1: "苹果", 2: "香蕉", 3: "橙子", 4: "葡萄"}
    # list()生成静态键列表，与原字典解耦
    for k in list(data.keys()):
        if k % 2 != 0:
            del data[k]
    print(data)
# 输出 {2: '香蕉', 4: '葡萄'}

def fix_batch_modify():
    data = {"a": 10, "b": 20}
    add_list = []
    # 仅筛选，不修改原字典
    for k in data.keys():
        add_list.append((k + "_new", data[k] * 2))
    # 循环结束后统一新增
    for new_k, val in add_list:
        data[new_k] = val
    print(data)

def fix_by_comprehension():
    data = {1: "苹果", 2: "香蕉", 3: "橙子", 4: "葡萄"}
    # 仅保留偶数键，生成新字典
    new_data = {k: v for k, v in data.items() if k % 2 == 0}
    print(new_data)