无法从python 3.6中的外部文件打印数据

在python 3.6中截断数据后，我试图从外部文件（test.txt）打印数据

但是，当我在使用 write() 写入后尝试使用 open() 和 read() 执行此操作时，它不起作用。

from sys import argv
script,filename=argv
print(f"We're going to erase {filename}.")
print("If you don't want that, hit CTRL-C (^C).")
print("If you do want that, hit RETURN.")
input("?")

print("Opening the file...")
target=open(filename,"w")

print("Truncating the file. Goodbye!")
target.truncate()

print("Now I'm going to ask you for the three lines.")
line1=input("line 1: ")
line2=input("line 2: ")
line3=input("line 3: ")

print("I'm going to write these to the file")
target.write(line1 + "\n" + line2 + "\n" + line3 + "\n")
a=input("Please type the filename once again:")
b=open(a)
c=b.read()
print(c)
print("And finally, we close it.")
target.close()

不确定，我做错了什么？