python如何将文件a.txt的内容复制到b.txt中

# 1. 用r方式打开a.txt
f = open("a.txt","r")
# 2. 读取a.txt的内容
buf = f.read()
# 3. 关闭a.txt
f.close
# 4. 用w或者a的方式打开b.txt
f = open("b.txt","w")
# 5. 将文件写入b.txt中
f.write(buf)
# 6. 关闭b.txt
f.close() 

with open(filepath,'w') as f:
    f.write(line) 

import os
import re
import sys

mefile_name=['D:\\LDA\\LdaStemDocs2\\breast cancer\\','D:\\LDA\\LdaStemDocs2\\colon cancer\\','D:\\LDA\\LdaStemDocs2\\lung cancer\\','D:\\LDA\\LdaStemDocs2\\NHL\\','D:\\LDA\\LdaStemDocs2\\pancreatic cancer\\','D:\\LDA\\LdaStemDocs2\\prostate cancer\\','D:\\LDA\\LdaStemDocs2\\urinary bladder cancer\\']
for i in range(len(mefile_name)):
    for j in range(len(datil_name)):
        meragefiledir=mefile_name[i]+datil_name[j]
        filenames=os.listdir(meragefiledir)
        filestore_name='\\result_.txt'
        with open(filestore_name,'w',encoding='utf-8') as f:
            for filename in filenames:
                filepath=meragefiledir+'\\'
                filepath=filepath+filename
                for line in open(filepath).readlines():
                    line=re.findall(r'[a-zA-Z]+\s+[a-zA-Z\s]*',line)
                    line="".join(line)  
            #print(line)
                    f.write(line+'\n')
            #f.write('\n')
        print('combine {0}{1} ending~~~~~~\n'.format(mefile_name[i],datil_name[j]))
print('ending all')