python pandas excel reading and writing

It is the first time for a python novice to use pandas. It is still difficult to read the detailed tutorials, so I will record a few things I know how to use.
1.Read excel

import pandas as pd
df = pd.read_excel(r'D:/filename.xlsx') #读取整个xlsx
df1 = pd.read_excel(r'D:/filename.xlsx', usecols=[0]).dropna(axis=0)#读取第一列，并去除NAN
df2 = pd.read_excel(r'D:/filename.xlsx', usecols=[1]).dropna(axis=0)
df7 = pd.read_excel(r'D:/filename.xlsx', usecols='A')
df8 = pd.read_excel(r'D:/filename.xlsx', usecols='A:B,D').dropna(axis=0)#多列去除NAN，会保留最短列的长度，长列被截断

2. Remove NAN

df9=df1.dropna(axis=0)

3. See what these are

print('df1的类型是：',type(df1))#df1的类型是： <class 'pandas.core.frame.DataFrame'>
print('size的类型是：',type(df1.size))#size的类型是： <class 'numpy.int32'>
print("int(size)的类型是:",type(int(df1.size)))#int(size)的类型是: <class 'int'>

4. Read data

df8.iloc[2,1:]

5. Save to excel

df_res=pd.DataFrame(b)
print('df_res:',df_res)
df_res.to_excel(r'D:/235_011.xlsx')