Question

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)  

# we could do these two on one line too, how?

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

print "The input file is %d bytes long" % len(indata)

print "Does the output file exist? %r" % exists(to_file)
print "Ready, hit RETURN to continue, CTRL-C to abort."
raw_input()

output = open(to_file, 'w')
output.write(indata)

print "Alright, all done."

output.close()
input.close()

Answer 1

Python的with语句在这里很方便。当你处理文件时，它习惯于使用它，因为它会处理掉对象并捕获异常。

您可以在documentation。

中阅读相关内容

以下是您在计划中使用with的方法：

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)

with open(from_file) as input, open(to_file, 'w') as output:

    print "The input file is %d bytes long" % len(input.read())
    print "Does the output file exist? %r" % exists(to_file)
    raw_input("Ready, hit RETURN to continue, CTRL-C to abort.")

    output.write(input.read())
    print "Alright, all done."

单线 -

with open(from_file) as in, open(to_file, 'w') as o: o.write(in.read())

提示：将所有这些代码写在一行中会降低其可读性。但是，python支持;作为行终止符。

所以你可以这样做：

print foo(); print bar(); print baz();

但请记住python的冒号:运算符的优先级高于;。因此，如果我们写 -

if True: print foo(); print bar();

这里要么所有的print语句都会执行，要么都不执行。

Answer 2

我不知道为什么你会关心你的代码中的物理行数，但这里有一些非常简洁的东西（随意编辑任何空白行）

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)  

with open(from_file) as infile: indata = infile.read()


print "The input file is %d bytes long" % len(indata)

print "Does the output file exist? %s" % 'no yes'.split()[int(exists(to_file))]
raw_input("Ready, hit RETURN to continue, CTRL-C to abort.")

with open(to_file, 'w') as outfile: output.write(indata)

print "Alright, all done."

或者，这是另一个版本：

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)

with open(from_file) as infile, open(to_file, 'w') as outfile:
    indata = infile.read()
    print "The input file is %d bytes long" % len(indata)
    print "Does the output file exist? %s" % 'no yes'.split()[int(exists(to_file))]
    raw_input("Ready, hit RETURN to continue, CTRL-C to abort.")
    output.write(indata)

print "Alright, all done."

如何在python中的一行中写这个

2 个答案: