Question

这是我为此目的编写的Python代码：

from sys import argv
from os.path import exists

script, filenamefrom, filenameto = argv

print "We're going to erase %r." % filenamefrom
print "If you don't want that, hit CTRL-C (^C)."
print "If you do want that, hit RETURN."

raw_input("?")

print "Opening the file..."
target = open(filenamefrom,'w+')

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."

target.write('%r\n%r\n%r\n' % (line1, line2, line3))

print "Now we are going to copy %r to %r!" % (filenamefrom, filenameto)



readdata = target.read()
openfilenameto = open(filenameto,'w+')
openfilenameto.write(readdata)


print "And finally, we close it."

openfilenameto.close()
target.close()

现在，当我在Powershell中运行时，会出现这种情况：

We're going to erase 'test.txt'.
If you don't want that, hit CTRL-C (^C).
If you do want that, hit RETURN.
?
Opening the file...
Truncating the file. Goodbye!
Now I'm going to ask you for three lines.
line 1: h
line 2: h
line 3: h
I'm going to write these to the file.
Now we are going to copy 'test.txt' to 'test4.txt'!
And finally, we close it.

然而 - 一旦我跑：

cat test4.txt

在Windows Powershell中，这是它输出的内容 - 在以下行之后没有任何内容，尽管该空白空间在以下行后面的Powershell页面34行中显示：

PS C:\python27> cat test4.txt

我尝试更改＆＃39; r +＆＃39;之间的文件模式模块。并且＆＃39; w +＆＃39;整个Python代码，但这不起作用。

另外 - 我知道这是烦人且重复的代码，但我对此很陌生，并且仍在提高我缩短代码的技能。为此道歉，我感谢任何可能回复的人的耐心。

感谢。

Answer 1

问题是，您没有将read和write分开。

将缓冲区写入文件后，文件指针位于文件末尾。如果再次使用read()，则告诉文件描述符从该点读取，即从文件末尾读取。当然没有什么可读的......所以你什么都没得到; - ）

尝试将您的写入/读取分开或将文件描述符再次放到开头（使用seek），然后就完成了。

还可以使用with语句来简化代码并将相关的行放在一起。

这是更新的脚本，有一个更好的解决方案：

from sys import argv
from os.path import exists

script, filenamefrom, filenameto = argv

print "We're going to erase %r." % filenamefrom
print "If you don't want that, hit CTRL-C (^C)."
print "If you do want that, hit RETURN."

raw_input("?")

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 "Opening the file..."
with open(filenamefrom, 'w+') as target_file:
    print "Truncating the file. Goodbye!"
    target_file.truncate()
    print "I'm going to write these to the file."
    target_file.write('%r\n%r\n%r\n' % (line1, line2, line3))

print "Now we are going to copy %r to %r!" % (filenamefrom, filenameto)

with open(filenamefrom, 'r') as target_file:
    readdata = target_file.read()
    with open(filenameto, 'w+') as to_file:
        to_file.write(readdata)

但是，有更好的方法可以复制文件，例如：

from shutil import copyfile
copyfile(filenamefrom, filenameto)

Python - 尝试截断，写入然后将写入文件复制到另一个文件

1 个答案: