On 22/08/12 08:06, Peter Otten wrote:
You can even have multiple if clauses in one list-comp (but that is rarely
used):
with open(filename) as lines:
wanted = [line.strip("\n") for line
if "vn" not in line
if "vt" not in x
if line != "\n"]
While your problem is simple enough to combine all filters into one list-
comp some problems are not. You can then prevent the intermediate lists from
materializing by using generator expressions. The result minimizes memory
consumption, too, and should be (almost) as fast. For example:
with open(filename) as lines:
# use gen-exps to remove empty and whitespace-only lines
stripped = (line.strip() for line in lines)
nonempty = (line for line in stripped if line)
wanted = [line for line in nonempty
if "vt" not in line and "vn" not in line]
Another option using generators is to roll your own. This would be my
recomendation for really complex filtering:
def myFilterGenerator(aFile):
for line in aFile:
if 'vn' not in line: # demo "complexity" not efficiency!
if 'vt' not in line:
if '\n' != line:
yield line.strip()
with open filename as myFile:
result = [line for line in myFilterGenerator(myFile)]
But in this specific case the filter is simple enough that the
list comp from Peter is probably the best solution.
HTH
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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