DataFrame数据转为IO文件流
用于网页后端导出excel时，响应数据类型设置为stream
pandas Writing Excel files to memory
from io import BytesIO
bio = BytesIO()
# writer = pd.ExcelWriter(bio, engine="xlsxwriter") # 可行引擎 openpyxl
# 使用with
with pd.ExcelWriter(bio, engine="xlsxwriter") as writer:
df.to_excel(writer, sheet_name="Sheet1")
# 调用流数据
bio.seek(0)
# return bio