python如何处理excel数据？

import pandas as pd
import numpy as np
import csv,datetime

def mjdfb(x):
    if x<120:
        return '90-120方'
    elif x<140:
        return '120-140方'
    return '140方以上'

def yszzt(x):
    if int(x)==0:
        return '未取证'
    elif int(x)<int('43890'):
        return '已取证'
    return '未取证'

def rgzt(x):
    if int(x)==0:
        return '未认购'
    elif int(x)>int('43890'):
        return '未认购'
    return '已认购'

def qyzt(x):
    if int(x)==0:
        return '未签约'
    elif int(x)>int('43890'):
        return '未签约'
    return '已签约'

def wqzt(x):
    if int(x)==0:
        return '未网签'
    elif int(x)>int('43890'):
        return '未网签'
    return '已网签'

if __name__=='__main__':
    csv_file=open('房源清单处理.csv','w+',newline='',encoding='utf-8')
    writer=csv.writer(csv_file)
    fileName=r'/Users/Desktop/python/python生成现金流套表/房源清单.csv'
    df=pd.read_csv(fileName)

    df['面积段分布']=df.预测建筑面积.apply(mjdfb)
    df['预售证状态']=df.预售许可证取证日期.apply(yszzt)
    df['认购状态']=df.认购日期.apply(rgzt)
    df['签约状态']=df.签约日期.apply(qyzt)
    df['网签状态']=df.网签日期.apply(wqzt)
    df['已取证未认购']=df['预售证状态']+df['认购状态']
    df['已认购未签约']=df['认购状态']+df['签约状态']
    df['已签约未网签']=df['签约状态']+df['网签状态']

    # print('2020/1/1'-datetime.date.today())
    df.to_csv(csv_file)