如何创建全局数据帧？获取错误- UnboundLocalError:赋值前引用的局部变量

import pandas as pd

# 声明全局数据帧
global_df = None

def create_global_dataframe():
    global global_df
    # 创建数据帧
    data = {
        'A': [1, 2, 3],
        'B': [4, 5, 6]
    }
    global_df = pd.DataFrame(data)

# 调用函数创建全局数据帧
create_global_dataframe()

# 打印全局数据帧
print(global_df)

def example_function():
    print(local_var)  # 这里会引发 UnboundLocalError
    local_var = 10

example_function()

def example_function():
    local_var = 10
    print(local_var)

example_function()

local_var = None

def example_function():
    global local_var
    local_var = 10
    print(local_var)

example_function()

def example_function():
    if 'local_var' not in locals():
        local_var = 10
    print(local_var)

example_function()