'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.
|

[Wojtek Walczak]

Re: 'While' question

On Thu, 21 Aug 2008 18:01:25 -0400, Ben Keshet wrote:

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)

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

HTH.

--
Regards,
Wojtek Walczak,

http://tosh.pl/gminick/

[Ben Keshet]

Re: 'While' question

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


Wojtek Walczak wrote:

On Thu, 21 Aug 2008 18:01:25 -0400, Ben Keshet wrote:
>

>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)
>>

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

[Larry Bates]

Re: 'While' question

Ben Keshet wrote:

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
>
>
Wojtek Walczak wrote:

>On Thu, 21 Aug 2008 18:01:25 -0400, Ben Keshet wrote:
>>

>>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
>>ActivePytho n)
>>>

>>
>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]

Re: 'While' question

On Aug 22, 9:01 am, Ben Keshet <kesh...@umbc.e duwrote:

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]

Re: 'While' question

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

[Ben Finney]

Re: 'While' question

Bruno Desthuilliers <bruno.42.desth uilliers@websit eburo.invalidwr ites:

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

Merely a special case of the truism that "Your code is probably wrong
(regardless of any other properties it may show)".

That doesn't make John's quote any less worthy of QOTW, though :-)

--
\ “The problem with television is that the people must sit and |
`\ keep their eyes glued on a screen: the average American family |
_o__) hasn't time for it.” —_The New York Times_, 1939 |
Ben Finney