[Tutor] Re: print out lines that start with a word

[Wolfram Kraus]

Liam Clarke wrote:
>>>>x= ["Dude", 'How is it going man', '     ']
>>>>print x
> 
> ['Dude', 'How is it going man', '     ']
> 
> 
>>>>j=[]
>>>>for item in x:
> 
> ... 	if re.search('\S+',item):
> ... 		j.append(item)
> 
> 
>>>>print j
> 
> ['Dude', 'How is it going man']
What about:
x= ["Dude", 'How is it going man', '     ']
print [a for a in x if a.strip()]


> Now, I first did that in a Perl script, but it easily comes across to
> Python. \S+ will usually mean 'one or more non-whitespace characters'.
> Brilliant for when your first Perl script accidentally appended \n to
> everything, even \n and \t. *embarassed*
> 
> Whereas, while I'm sure there is a string method that can do that, I'm
> not sure what it is.
Well the documentation on that is not sooo big ;-)

> Also - say you have a list of words - 
> j = " bag apple tomato cheese *marmite*  sausages *scones*"
> 
> and you wanted to pick up each word that was asterisked. 
> I did this as a string method then a regex.
> 
> 
> 
>>>>try:
> 
> ... 	indexes=[]
> ... 	lastIndex = 0
> ... 	while 1:
> ... 		x = j.index("*", lastIndex + 1)
> ... 		indexes.append(x)
> ... 		lastIndex = x
> ... except ValueError:
> ... 	pass
> ... 
> 
>>>>print indexes
> 
> [4,  10]
> 
>>>>myString = j[5:10]
> 
That gives me  [25, 33, 45, 52], propably a C&P bug?

> Now the regular expression - 
> 
> 
>>>>x = re.finditer("\*(?P<myString>.*?)\*", j)
>>>>a = x.next()
>>>>print a.group('myString')
> 
> apple
Same error as above? And you said you want _all_ asteriksed words!
How about this cute lil list comprehension:
print [w for w in j.split() if words[0] == '*' and words[-1] == '*']

> Now, while the regEx syntax is a big harsh to begin with, once you get
> the hang of it, it's OK, and the string method version I used felt too
> 'hacky' for me. Of course, both only work with pairs of asterisks, so
> I guess that makes them both hacky. : )
> 
> That's my 2c, I use string methods for stuff like that .startswith, .endswith, 
> if 'foo' in x stuff is good as well. But sometimes, a regex is the
> right tool for the job.

I didn't say that they are useless (and don't wanna troll or start a 
flameware), but IMHO they are a PITA when it comes to debugging. Ever 
touched a regexp after one year ;-)?

> Regards, 
> 
> 
> Liam Clarke

Greetings,
Wolfram