Re: converting a sed / grep / awk / . . . bash pipe line into python
- From: Peter Otten <__peter__@xxxxxx>
- Date: Wed, 03 Sep 2008 09:15:17 +0200
hofer wrote:
Something I have to do very often is filtering / transforming line
based file contents and storing the result in an array or a
dictionary.
Very often the functionallity exists already in form of a shell script
with sed / awk / grep , . . .
and I would like to have the same implementation in my script
What's a compact, efficient (no intermediate arrays generated /
regexps compiled only once) way in python
for such kind of 'pipe line'
Example 1 (in bash): (annotated with comment (thus not working) if
copied / pasted
cat file \ ### read from file
| sed 's/\.\..*//' \ ### remove '//' comments
| sed 's/#.*//' \ ### remove '#' comments
| grep -v '^\s*$' \ ### get rid of empty lines
| awk '{ print $1 + $2 " " $2 }' \ ### knowing, that all remaining
lines contain always at least
\ ### two integers calculate
sum and 'keep' second number
| grep '^42 ' ### keep lines for which sum is 42
| awk '{ print $2 }' ### print number
thanks in advance for any suggestions of how to code this (keeping the
comments)
for line in open("file"): # read from file
try:
a, b = map(int, line.split(None, 2)[:2]) # remove extra columns,
# convert to integer
except ValueError:
pass # remove comments, get rid of empty lines,
# skip lines with less than two integers
else:
# line did start with two integers
if a + b == 42: # keep lines for which the sum is 42
print b # print number
The hard part was keeping the comments ;)
Without them it looks better:
import sys
for line in sys.stdin:
try:
a, b = map(int, line.split(None, 2)[:2])
except ValueError:
pass
else:
if a + b == 42:
print b
Peter
.
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