ex16-17---learn python the hard way

ex16

#-*- coding: UTF-8 -*- 
from sys import argv

script,filename = argv

print "We are going to erase %r." %filename
print "If you don't want that ,hit control-C(^C)"
print "If you do want that ,hit return."

raw_input("?")#通过输入回车进入下一步
print "opening the file..."
target = open(filename,'w')#默认情况下不加“w”,那么是以只读模式"r"打开的。


print "Truncating the file.Goodbye!"
target.truncate()#清空文档

print"Now I am going to ask you for three lines."

line1 = raw_input("line1:")
line2 = raw_input("line2:")
line3 = raw_input("line3:")#输入一二三行的内容

print "I'm going to write these to file."

#target.write("%s
%s
%s
" %(line1,line2,line3))

target.write("
")
target.write(line2)
target.write("
")  #注意换行符的斜杠方向

target.write(line3)
target.write("
")

print "And finally,we close it."
target.close()

附加练习2中要求用read 和argv读取刚建的文件。

#-*- coding: UTF-8 -*- 
from sys import argv
script,filename = argv

txt = open(filename)
print "Here is your file %r" %filename
print txt.read()#读取之后打印才能看到
txt.close()

附加练习3，试着用一个target.write()打印line1-line3，可以使用字符串、格式化字符和转义字符

target.write("%s
%s
%s
" %(line1,line2,line3))#这里注意括号里边的引号和括号

---

ex17

#-*- coding: UTF-8 -*- 
from sys import argv
from os.path import exists

script,from_file,to_file = argv

print "Copying from %s to %s" %(from_file,to_file)

in_file = open(from_file)
indata = in_file.read()

print "The input file is %d bytes long" %len(indata)
print "Does the output file exist?%r" %exists(to_file)

print"Ready,hit the return to continue,CTRL-C to abort."
raw_input()

out_file = open(to_file,"w")
out_file.write(indata)
print"Alrightm,all done."

out_file.close()
in_file.close()

#to_file 是string，无法 close,关闭需要关闭 in_file
#lens 可以用来读取文件的字节数
#exists 用来判断文件是否存在，然后返回布尔值

尽可能削减代码，自己重新写了一遍

#-*- coding: UTF-8 -*- 
from sys import argv
from os.path import exists

script,from_file,to_file = argv


in_file = open(from_file)
indata = in_file.read()


out_file = open(to_file,"w")
out_file.write(indata)

out_file.close()
in_file.close()

#试图压缩代码，想把以下两句合并成一句
#in_file = open(from_file)
#indata = in_file.read()
#in_file = open(from_file,"r")
#后来发现是错误的，因为这只是把文件以只读模式打开，并没有实现读的功能。


#-*- coding: UTF-8 -*- 
from sys import argv
script,from_file,to_file = argv

what_to_copy = open(from_file)
out_file = open(to_file,"w")
out_file.write(what_to_copy.read())

what_to_copy.close()
out_file.close()

#自己写的程序：实际上只需要这么几个流程：打开文件1-读取文件1-打开文件2-复制到文件2-关闭文件1/2

#尝试写成一行：

 from sys import argv
 script, from_file, to_file = argv
 open(to_file, 'w').write(open(from_file).read()

附加题中关于cat ，相同功能的还有在powershell下可以使用get-content [-Path]来读取txt文件