[英]Read from File, or STDIN
I've written a command line utility that uses getopt for parsing arguments given on the command line.我编写了一个命令行实用程序,它使用 getopt 来解析命令行上给出的 arguments。 I would also like to have a filename be an optional argument, such as it is in other utilities like grep, cut etc. So, I would like it to have the following usage我还想让文件名成为可选参数,例如在 grep、cut 等其他实用程序中。所以,我希望它具有以下用法
tool -d character -f integer [filename]
How can I implement the following?我该如何实施以下内容?
The fileinput module may do what you want - assuming the non-option arguments are in args
then: fileinput模块可以做你想做的 - 假设非选项参数在args
那么:
import fileinput
for line in fileinput.input(args):
print line
If args
is empty then fileinput.input()
will read from stdin;如果args
为空,则fileinput.input()
将从标准输入读取; otherwise it reads from each file in turn, in a similar manner to Perl's while(<>)
.否则它会依次从每个文件中读取,类似于 Perl 的while(<>)
。
In the simplest terms:用最简单的话来说:
import sys
# parse command line
if file_name_given:
inf = open(file_name_given)
else:
inf = sys.stdin
At this point you would use inf
to read from the file.此时,您将使用inf
从文件中读取。 Depending on whether a filename was given, this would read from the given file or from stdin.根据是否给定文件名,这将从给定的文件或标准输入读取。
When you need to close the file, you can do this:当您需要关闭文件时,您可以这样做:
if inf is not sys.stdin:
inf.close()
However, in most cases it will be harmless to close sys.stdin
if you're done with it.然而,在大多数情况下,如果你完成了关闭sys.stdin
是无害的。
I like the general idiom of using a context manager, but the (too) trivial solution ends up closing sys.stdin
when you are out of the with
statement, which I want to avoid.我喜欢使用上下文管理器的一般习惯用法,但是当您退出with
语句时,(太)琐碎的解决方案最终会关闭sys.stdin
,我想避免这种情况。
Borrowing from this answer , here is a workaround:借用这个答案,这是一个解决方法:
import sys
import contextlib
@contextlib.contextmanager
def _smart_open(filename, mode='Ur'):
if filename == '-':
if mode is None or mode == '' or 'r' in mode:
fh = sys.stdin
else:
fh = sys.stdout
else:
fh = open(filename, mode)
try:
yield fh
finally:
if filename != '-':
fh.close()
if __name__ == '__main__':
args = sys.argv[1:]
if args == []:
args = ['-']
for filearg in args:
with _smart_open(filearg) as handle:
do_stuff(handle)
I suppose you could achieve something similar with os.dup()
but the code I cooked up to do that turned out to be more complex and more magical, whereas the above is somewhat clunky but very straightforward.我想你可以用os.dup()
实现类似的东西,但我编写的代码变得更加复杂和神奇,而上面的代码有点笨拙但非常简单。
I prefer to use "-" as an indicator that you should read from stdin, it's more explicit:我更喜欢使用“-”作为您应该从标准输入读取的指示符,它更明确:
import sys
with open(sys.argv[1], 'r') if sys.argv[1] is not "-" else sys.stdin as f:
pass # do something here
To make use of python's with
statement, one can use the following code:要使用 python 的with
语句,可以使用以下代码:
import sys
with open(sys.argv[1], 'r') if len(sys.argv) > 1 else sys.stdin as f:
# read data using f
# ......
Not a direct answer but related.不是直接的答案,而是相关的。
Normally when you write a python script you could use the argparse
package.通常,当您编写 python 脚本时,您可以使用argparse
包。 If this is the case you can use:如果是这种情况,您可以使用:
parser = argparse.ArgumentParser()
parser.add_argument('infile', nargs='?', type=argparse.FileType('r'), default=sys.stdin)
'?'. '?'。 One argument will be consumed from the command line if possible, and produced as a single item.如果可能,将从命令行使用一个参数,并作为单个项目生成。 If no command-line argument is present, the value from default will be produced.如果不存在命令行参数,则将生成默认值。
and here we set default to sys.stdin
;在这里我们将默认设置为sys.stdin
;
so If there is a file it will read it , and if not it will take the input from stdin "Note: that we are using positional argument in the example above"所以如果有一个文件,它将读取它,如果没有,它将从标准输入中获取输入“注意:我们在上面的例子中使用了位置参数”
for more visit: https://docs.python.org/2/library/argparse.html#nargs更多访问: https : //docs.python.org/2/library/argparse.html#nargs
Switch to argparse
(it's also part of the standard library) and use an argparse.FileType
with a default value of stdin:切换到argparse
(它也是标准库的一部分)并使用默认值为 stdin 的argparse.FileType
:
import argparse, sys
p = argparse.ArgumentParser()
p.add_argument('input', nargs='?',
type=argparse.FileType(), default=sys.stdin)
args = p.parse_args()
print(args.input.readlines())
This will not let you specify encoding and other parameters for stdin, however;但是,这不会让您为 stdin 指定编码和其他参数; if you want to do that you need to make the argument non-optional and let FileType
do its thing with stdin when -
is given as an argument:如果你想这样做,你需要使参数成为非可选的,并让FileType
在-
作为参数给出时使用 stdin 做它的事情:
p.add_argument('input', type=FileType(encoding='UTF-8'))
Take heed that this latter case will not honour binary mode ( 'b'
) I/O.请注意,后一种情况将不支持二进制模式 ( 'b'
) I/O。 If you need only that, you can use the default argument technique above, but extract the binary I/O object, eg, default=sys.stdout.buffer
for stdout.如果您只需要它,您可以使用上面的默认参数技术,但提取二进制 I/O 对象,例如,对于 stdout, default=sys.stdout.buffer
。 However, this will still break if the user specifies -
anyway.但是,如果用户指定-
无论如何,这仍然会中断。 (With -
stdin/stdout is always wrapped in a TextIOWrapper
.) (使用-
stdin/stdout 始终包装在TextIOWrapper
。)
If you want it to work with -
, or have any other arguments you need to provide when opening the file, you can fix the argument if it got wrapped wrong:如果您希望它与-
,或者在打开文件时需要提供任何其他参数,则可以在包装错误时修复该参数:
p.add_argument('output', type=argparse.FileType('wb'))
args = p.parse_args()
if hasattr(args.output, 'buffer'):
# If the argument was '-', FileType('wb') ignores the 'b' when
# wrapping stdout. Fix that by grabbing the underlying binary writer.
args.output = args.output.buffer
(Hat tip to medhat for mentioning add_argument()
's type
parameter.) (提示medhat提及add_argument()
的type
参数。)
Something like:就像是:
if input_from_file:
f = open(file_name, "rt")
else:
f = sys.stdin
inL = f.readline()
while inL:
print inL.rstrip()
inL = f.readline()
A KISS solution is: KISS 解决方案是:
if file == "-":
content = sys.stdin.read()
else:
with open(file) as f:
content = f.read()
print(content) # Or whatever you want to do with the content of the file.
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