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How to remove empty lines with re?

ted
I'm having trouble using the re module to remove empty lines in a file.

Here's what I thought would work, but it doesn't:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub(r'^\s+$|\n', '', line)
print line

Also, when I try to remove some HTML tags, I get even more empty lines:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub('<.*?>', '', line)
line = re.sub(r'^\s+$|\n', '', line)
print line

I don't know what I'm doing. Any help appreciated.

TIA,
Ted


Jul 18 '05 #1
9 21810
"ted" <te************@yahoo.com> writes:
f = open("old_site/index.html")
for line in f:
line = re.sub(r'^\s+$|\n', '', line) # }
print line # }

If you will set a variable to an empty string and then print it, you will
get an empty line printed ;)

~Tim
--
Product Development Consultant
OpenLink Software
Tel: +44 (0) 20 8681 7701
Web: <http://www.openlinksw.com>
Universal Data Access & Data Integration Technology Providers
Jul 18 '05 #2
ted wrote:
I'm having trouble using the re module to remove empty lines in a file.

Here's what I thought would work, but it doesn't:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub(r'^\s+$|\n', '', line)
print line


Try:

import sys
for line in f:
if line.strip():
sys.stdout.write(line)

Background: lines read from the file keep their trailing "\n", a second
newline is inserted by the print statement.
The strip() method creates a copy of the string with all leading/trailing
whitespace chars removed. All but the empty string evaluate to True in the
if statement.

Peter
Jul 18 '05 #3

"ted" <te************@yahoo.com> wrote in message
news:vo************@corp.supernews.com...
I'm having trouble using the re module to remove empty lines in a file.

Here's what I thought would work, but it doesn't:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub(r'^\s+$|\n', '', line)
print line


nonempty = [x for x in f if not x.strip()]

/BJ
Jul 18 '05 #4
To do this, you need to modify your re to just
this

empty=re.compile('^$')

This of course looks for a pattern where there is beginning just
after end, ie the line is empty :-)

Here is the complete code.

import re

empty=re.compile('^$')
for line in open('test.txt').readlines():
if empty.match(line):
continue
else:
print line,

The comma at the end of the print is to avoid printing another newline,
since the 'readlines()' method gives you the line with a '\n' at the end.

Also dont forget to compile your regexps for efficiency sake.

HTH

-Anand Pillai
"ted" <te************@yahoo.com> wrote in message news:<vo************@corp.supernews.com>...
I'm having trouble using the re module to remove empty lines in a file.

Here's what I thought would work, but it doesn't:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub(r'^\s+$|\n', '', line)
print line

Also, when I try to remove some HTML tags, I get even more empty lines:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub('<.*?>', '', line)
line = re.sub(r'^\s+$|\n', '', line)
print line

I don't know what I'm doing. Any help appreciated.

TIA,
Ted

Jul 18 '05 #5
Errata:

I meant "there is end just after the beginning" of course.

-Anand

"ted" <te************@yahoo.com> wrote in message news:<vo************@corp.supernews.com>...
I'm having trouble using the re module to remove empty lines in a file.

Here's what I thought would work, but it doesn't:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub(r'^\s+$|\n', '', line)
print line

Also, when I try to remove some HTML tags, I get even more empty lines:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub('<.*?>', '', line)
line = re.sub(r'^\s+$|\n', '', line)
print line

I don't know what I'm doing. Any help appreciated.

TIA,
Ted

Jul 18 '05 #6
Anand Pillai wrote:
Here is the complete code.

import re

empty=re.compile('^$')
for line in open('test.txt').readlines():
if empty.match(line):
continue
else:
print line,
The .readlines() method retains any line terminators, and using the
builtin print will suffix an extra line terminator to every line,
thus effectively producing an empty line for every non-empty line.
You'd want to use e.g. sys.stdout.write() instead of print.
// Klaus

--<> unselfish actions pay back better

Jul 18 '05 #7
ted
Thanks Anand, works great.
"Anand Pillai" <py*******@Hotpop.com> wrote in message
news:84**************************@posting.google.c om...
To do this, you need to modify your re to just
this

empty=re.compile('^$')

This of course looks for a pattern where there is beginning just
after end, ie the line is empty :-)

Here is the complete code.

import re

empty=re.compile('^$')
for line in open('test.txt').readlines():
if empty.match(line):
continue
else:
print line,

The comma at the end of the print is to avoid printing another newline,
since the 'readlines()' method gives you the line with a '\n' at the end.

Also dont forget to compile your regexps for efficiency sake.

HTH

-Anand Pillai
"ted" <te************@yahoo.com> wrote in message

news:<vo************@corp.supernews.com>...
I'm having trouble using the re module to remove empty lines in a file.

Here's what I thought would work, but it doesn't:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub(r'^\s+$|\n', '', line)
print line

Also, when I try to remove some HTML tags, I get even more empty lines:

import re
f = open("old_site/index.html")
for line in f:
line = re.sub('<.*?>', '', line)
line = re.sub(r'^\s+$|\n', '', line)
print line

I don't know what I'm doing. Any help appreciated.

TIA,
Ted

Jul 18 '05 #8
You probably did not read my posting completely.

I have added a comma after the print statement and mentioned
a comment specifically on this.

The 'print line,' statement with a comma after it does not print
a newline which you also call as line terminator whereas
the 'print' without a comma at the end does just that.

No wonder python sometimes feels like high-level psuedocode ;-)
It has that ultra intuitive feel for most of its tricks.

In this case, the comma is usually put when you have more than
one item to print, and python puts a newline after all items.
So it very intuitively follows that just putting a comma will not
print a newline! It is better than telling the programmer to use
another print function to avoid newlines, which you find in many
other 'un-pythonic' languages.

-Anand

Klaus Alexander Seistrup <sp**@magnetic-ink.dk> wrote in message news:<3f****************************************** *@news.szn.dk>...
Anand Pillai wrote:
Here is the complete code.

import re

empty=re.compile('^$')
for line in open('test.txt').readlines():
if empty.match(line):
continue
else:
print line,


The .readlines() method retains any line terminators, and using the
builtin print will suffix an extra line terminator to every line,
thus effectively producing an empty line for every non-empty line.
You'd want to use e.g. sys.stdout.write() instead of print.
// Klaus

Jul 18 '05 #9
Anand Pillai wrote:
You probably did not read my posting completely.

I have added a comma after the print statement and mentioned
a comment specifically on this.
You are completely right, I missed an important part of your posting.
I didn't know about the comma feature, so thanks for teaching me!

Cheers,

// Klaus

--<> unselfish actions pay back better

Jul 18 '05 #10

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