pandas對excel遍歷讀取與填充：涉及多張表的保存、NAN的類型處理、NAN的處理（str類型下）

代碼如下：

import pandas as pd

stemp2 = "C:\\Users\\lenovo\\Desktop\\數據庫\\"
pos = stemp2 + "小學\\" + "數學" + ".xlsx"

df1 = pd.read_excel(pos, sheet_name="repository", dtype={"涉及題目": str})
df1 = df1.set_index("ID")
df2 = pd.read_excel(pos, sheet_name="problems")
df2 = df2.set_index("ID")

for i in df2["涉及知識點"].index:
    id_know = df2["涉及知識點"].at[i]
    id_know = int(id_know)
    if df1["涉及題目"].at[id_know] == "nan":
        df1["涉及題目"].at[id_know] = str(i)
    else:
        df1["涉及題目"].at[id_know] += " "
        df1["涉及題目"].at[id_know] += str(i)

writer = pd.ExcelWriter(pos)
df1.to_excel(writer, sheet_name="repository")
df2.to_excel(writer, sheet_name="problems")
writer.save()