笨办法学习python3练习代码：argv参数变量与文件操作

 1 from sys import argv
 2 #sys是一个软件包，把argv这个特性（或者叫模块、方法）插入到代码中
 3 script, filename = argv    #filename 是要选择读取的文件名，在这里是ex15_sample.txt
 4 
 5 #读取文件第一步，打开文件
 6 txt = open(filename)
 7 print(f"Here‘s your file {filename}:")
 8 
 9 #读取文件第二步，读文件并打印
10 print(txt.read())
11 #文件处理完，一定要关闭
12 txt.close()
13 
14 print("Type the filename again:")
15 
16 #input中“>”是提示符，打印出来就是>;用户输入的字符串会赋给变量file_again
17 file_again = input("> ")

18 txt_again = open(file_again)
19 print(txt_again.read())
20 #文件处理完，一定要关闭
21 txt_again.close()

 1 #close:关闭文件
 2 #read：读取文件的内容，可以把结果赋值给一个变量
 3 #readline：只读取文本文件的一行
 4 #truncate（缩短的意思）：清空文件，小心使用该命令
 5 #write("stuff"):将"stuff"写入文件
 6 #seek(0):将读写位置移动到文件开头
 7 
 8 from sys import argv
 9 script, filename = argv             #filename = ex15_sample.txt
10 print(f"We‘re going to erase {filename}.")  #erase ：清除的意思
11 
12 print("if you don‘t want that, hit CTRL-C {^C}.")  # hit 点击，打击的意思
13 print("if you do want that,hit RETURN.")
14 
15 input("?")
16 print("Opening the file...")
17 target = open(filename,‘w‘) #open for writing,truncating the file first
18 print("Truncate the file. Goodbye!")
19 
20 #清空文件 
21 target.truncate()
22 
23 print("Now I‘m going to ask you for threes lines.")
24 line1 = input("line 1: ")
25 line2 = input("line 2: ")
26 line3 = input("line 3: ")
27 
28 print("I‘m going to write these to the file.")
29 target.write(line1)
30 target.write("\n")
31 target.write(line2)
32 target.write("\n")
33 target.write(line3)
34 target.write("\n")
35 #一行一行接着写入
36 
37 print("And fianlly,we close it. ")
38 target.close()

 1 ‘‘‘
 2 把ex17_from.txt的内容 读取出来写入到ex17_to.txt 文件中
 3 1.打开ex17_from.txt文件，默认读方式打开
 4 2.读取文件数据
 5 3.关闭ex17_from.txt文件
 6 
 7 1.打开ex17_to.txt文件，默认读方式打开，改成写方式打开
 8 2.写入数据
 9 3.关闭ex17_to.txt文件
10 
11 
12 ‘‘‘
13 
14 
15 
16 from sys import argv
17 from os.path import exists  #exist(存在的意思)
18 
19 script, from_file, to_file = argv
20 print(f"coping from {from_file} to {to_file}")
21 in_file = open(from_file)
22 indata  = in_file.read()
23 print(f"The input file is {len(indata)}bytes long")
24 
25 print(f"Does the output file exists? {exists(to_file)} ")        #exist(存在的意思)
26 print("Ready,hit RETURN to continue, CTRL-C to abort.")
27 input()
28 in_file.close()
29 
30 out_file = open(to_file,‘w‘)
31 out_file.write(indata)
32 
33 print("Alright, all done.")
34 
35 out_file.close()