'While' question

[Ben Keshet]

Hi -

I am writing now my second script ever in python and need some help with
'while'. I am reading text from a set of files and manipulating the data
somehow. I use 'while 'word' not in line' to recognize words in the
texts. Sometimes, the files are empty, so while doesn't find 'word' and
runs forever. I have two questions:
1) how do I overcome this, and make the script skip the empty files?
(should I use another command?)
2) how do I interrupt the code without closing Python? (I have ActivePython)

I do know that the strings I am searching for are within the first say
50 lines.

Thanks!

Code:
|while 'PRIMARY' not in line:
line = f.readline()[:-1]
# copy scores
while 'es' not in line:
line = f.readline()[:-1]
out_file.write(line)
out_file.write(' ')
print
out_file.write('\n')
f.close()
out_file.close()

For example, 'PRIMARY' and 'es' do not exist when the file I am reading
(f) is empty.
|

 

[Ben Keshet]

Thanks for the reference. I tried it with a general example and got it
to work - I used an index that counts up to a threshold that is set to
break. It does not work though with my real code. I suspect this is
because I cannot really read any lines from an empty file, so the code
gets stuck even before I get to j=j+1:

line = f.readline()[:-1]
j=0
while 'PRIMARY' not in line:
line = f.readline()[:-1]
j=j+1
if j==30:
break

Any suggestions?

BK

 

[Larry Bates]

Thanks for the reference. I tried it with a general example and got it
to work - I used an index that counts up to a threshold that is set to
break. It does not work though with my real code. I suspect this is
because I cannot really read any lines from an empty file, so the code
gets stuck even before I get to j=j+1:

line = f.readline()[:-1]
j=0
while 'PRIMARY' not in line:
line = f.readline()[:-1]
j=j+1 if j==30:
break
Any suggestions?

BK

Try the docs first. You need to read about 'continue' and
'break' statements: http://docs.python.org/tut/node6.html

HTH.

You might consider turning this around into something like:


for j, line in enumerate(f):
if 'PRIMARY' in line:
continue

if j == 30:
break



IMHO this is MUCH easier to understand.

-Larry

 

[John Machin]

Thanks for the reference. I tried it with a general example and got it
to work - I used an index that counts up to a threshold that is set to
break. It does not work though with my real code. I suspect this is
because I cannot really read any lines from an empty file, so the code
gets stuck even before I get to j=j+1:

line = f.readline()[:-1]
j=0
while 'PRIMARY' not in line:
line = f.readline()[:-1]
j=j+1
if j==30:
break

Any suggestions?

(1) don't top-post
(2) use a 'for' statement
(3) readline is antique
(4) don't throw away the last character in the line without knowing
what it is

for line in f:
line = line.rstrip('\n')
# do something useful here
if 'PRIMARY' in line:
break
# do more useful stuff here

A quick rule of thumb for Python: if your code looks ugly or strained
or awkward, it's probably also wrong.

HTH,
John

 

[Bruno Desthuilliers]

John Machin a écrit :
(snip)

A quick rule of thumb for Python: if your code looks ugly or strained
or awkward, it's probably also wrong.

+1 QOTW