在python中使用“w”模式有什么意义？

Question

#From the sys package, i'm importing the argv
from sys import argv
#Un packaging the arguments
script, filename = argv 
#Print statements
print "We're going to erase %r." % filename
print "If you don't want that, hit CTRL-C (^C)."
print "If you do want that, hit RETURN."
#To accept whether or not we want to continue or not
raw_input("?")

print "Opening the file..."
# I am opening the file
target = open(filename)

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

print "Now i'm going to ask you for three lines."

line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")

print "I'm going to write these to the file."
x = "%r\n %r\n %r\n" % (line1, line2, line3)
target.write(x)
#This also works to write the files
# target.write ("%r\n%r\n%r\n" % (line1, line2, line3))

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

对于open(filename)，当我将脚本作为open(filename "w")

运行时，我发现我得到了相同的结果

那么“w”有什么意义呢？因为我已经有了使用target.write（）命令编写的函数！

Answer 1

“w”模式会创建该文件（如果该文件不存在），如果存在，则将其清空。

Answer 2

根据the docs for open()：

  

最常用的模式值是'r'用于读取，'w'用于写入（如果文件已经存在则截断文件）和'a'用于追加（在某些Unix系统上表示所有写入都附加）无论当前的搜索位置如何，都到文件的末尾。如果省略mode，则默认为'r'。