Jon Redgrave wrote:
> It seems unreasonably hard to write simple one-line unix command line
> filters in python:
>
> eg: ls | python -c "<something> print x.upper()"
>
> to get at sys.stdin or similar needs an import, which makes a
> subsequent for-loop illegal.
> python -c "import sys; for x in sys.stdin(): print x" <<- SyntaxError
>
> Am I missing something obvious?
>
> The best I've come up with is to use sitecustomize.py to add to
> __builtin__
> def stdin():
> import sys
> for x in sys.stdin():
> if not x: return
> yield x.strip()
> import __builtin__
> __builtin__.stdin = stdin
>
> This allows
> ls | python -c "for x in stdin(): print x.upper()"
>
> Is there a better solution - if not is this worth a PEP?
$ touch alpha beta gamma omega
$ ls | python -c 'import sys; sys.stdout.writelines(s.upper() for s in
sys.stdin if s.startswith(("a", "o")))'
ALPHA
OMEGA
If you are doing this a lot, why don't you write a helper script and invoke
that?
$ ls | pyfilter.py -f '"m" in line' -s 'lines = (line + line[::-1] for line
in map(str.strip, lines))' -s'import re' -p 're.compile(r"(([a-
z])\2)").sub(lambda m: m.group(1).upper(), line)'
alphAAhpla
betAAteb
gaMMAAMMag
omegAAgemo
This relies on the convention that a single line of input is accessible as
"line" and the complete input is called "lines". Of course the same can be
done with python -c ..., -- and it is even more readable:
$ ls | python -c 'import re, sys
for line in sys.stdin:
> line = line.strip()
> line = line + line[::-1]
> print re.compile(r"(([a-z])\2)").sub(lambda m: m.group(1).upper(),
line)
> '
alphAAhpla
betAAteb
gaMMAAMMag
omegAAgemo
> Is there a better solution - if not is this worth a PEP?
The python interpreter could accept multiple -c arguments, but to see how
this will be received a post on python-ideas should be sufficient.
For the sake of completeness here's the script I used to produce the example
above:
$ cat pyfilter.py
#!/usr/bin/env python
import sys
def main():
import argparse
parser = argparse.ArgumentParser()
parser.add_argument(
"-s", "--setup",
action="append", default=[],
dest="setups", metavar="SETUP")
parser.add_argument(
"-f", "--filter",
action="append", default=[],
dest="filters", metavar="FILTER")
parser.add_argument("-p", "--print", dest="format")
args = parser.parse_args()
lines = sys.stdin
for setup in args.setups:
exec setup
for line in lines:
line = line.rstrip("\n")
for filter in args.filters:
if not eval(filter):
continue
if args.format:
line = eval(args.format)
try:
print line
except IOError as e:
if e.errno == 32: # broken pipe
break
raise
if __name__ == "__main__":
main()
--
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