如何根据参数输入实现STDOUT和文件写入

Question

我的输入文件看起来像 this (infile.txt):

a x
b y
c z

我想实现一个程序，使用户能够根据命令写入 STDOUT 或文件：

python mycode.py infile.txt outfile.txt

将写入文件。

还有这个

python mycode.py infile.txt #2nd case

将写入 STDOUT。

我受困于这段代码：

import sys
import csv

nof_args = len(sys.argv)
infile  = sys.argv[1]

print nof_args
outfile = ''
if nof_args == 3:
    outfile = sys.argv[2]

# for some reason infile is so large
# so we can't save it to data structure (e.g. list) for further processing
with open(infile, 'rU') as tsvfile:
    tabreader = csv.reader(tsvfile, delimiter=' ')

    with open(outfile, 'w') as file:
        for line in tabreader:
            outline = "__".join(line)
            # and more processing
            if nof_args == 3:
                file.write(outline + "\n")
            else:
                print outline
    file.close()

当使用第二种情况时，它会产生

Traceback (most recent call last):
  File "test.py", line 18, in <module>
    with open(outfile, 'w') as file:
IOError: [Errno 2] No such file or directory: ''

实施它的更好方法是什么？

Answer 1

你可以试试这个：

import sys

if write_to_file:
    out = open(file_name, 'w')
else:
    out = sys.stdout

# or a one-liner:
# out = open(file_name, 'w') if write_to_file else sys.stdout

for stuff in data:
    out.write(stuff)

out.flush() # cannot close stdout

# Python deals with open files automatically

你也可以用这个代替 out.flush():

try:
    out.close()
except AttributeError:
    pass

我觉得这有点难看，所以，flush 就好了。

如何根据参数输入实现STDOUT和文件写入

How to implement STDOUT and file write based on parameter input

python

stdout

file