[Tutor] RegEx query
Hi all,
Using Beautiful Soup and regexes.. I've noticed that all the examples
used regexes like so - anchors = parseTree.fetch("a",
{"href":re.compile("pattern")} ) instead of precompiling the pattern.
Myself, I have the following code -
>>> z = []
>>> x = q.findNext("a", {"href":re.compile(".*?thread/[0-9]*?/.*",
re.IGNORECASE)})
>>> while x:
... num = x.findNext("td", "tableColA")
... h = (x.contents[0],x.attrMap["href"],num.contents[0])
... z.append(h)
... x = x.findNext("a",{"href":re.compile(".*?thread/[0-9]*?/.*",
re.IGNORECASE)})
...
This gives me a correct set of results. However, using the following -
>>> z = []
>>> pattern = re.compile(".*?thread/[0-9]*?/.*", re.IGNORECASE)
>>> x = q.findNext("a", {"href":pattern)})
>>> while x:
... num = x.findNext("td", "tableColA")
... h = (x.contents[0],x.attrMap["href"],num.contents[0])
... z.append(h)
... x = x.findNext("a",{"href":pattern} )
will only return the first found tag.
Is the regex only evaluated once or similar?
(Also any pointers on how to get negative lookahead matching working
would be great.
the regex (/thread/[0-9]*)(?!\/) still matches "/thread/28606/" and
I'd assumed it wouldn't.
Regards,
Liam Clarke
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Re: [Tutor] RegEx query
Liam Clarke wrote:
> Hi all,
>
> Using Beautiful Soup and regexes.. I've noticed that all the examples
> used regexes like so - anchors = parseTree.fetch("a",
> {"href":re.compile("pattern")} ) instead of precompiling the pattern.
>
> Myself, I have the following code -
>
z = []
x = q.findNext("a", {"href":re.compile(".*?thread/[0-9]*?/.*",
>
> re.IGNORECASE)})
>
>
while x:
>
> ... num = x.findNext("td", "tableColA")
> ... h = (x.contents[0],x.attrMap["href"],num.contents[0])
> ... z.append(h)
> ... x = x.findNext("a",{"href":re.compile(".*?thread/[0-9]*?/.*",
> re.IGNORECASE)})
> ...
>
> This gives me a correct set of results. However, using the following -
>
>
z = []
pattern = re.compile(".*?thread/[0-9]*?/.*", re.IGNORECASE)
x = q.findNext("a", {"href":pattern)})
>
>
while x:
>
> ... num = x.findNext("td", "tableColA")
> ... h = (x.contents[0],x.attrMap["href"],num.contents[0])
> ... z.append(h)
> ... x = x.findNext("a",{"href":pattern} )
>
> will only return the first found tag.
>
> Is the regex only evaluated once or similar?
I don't know why there should be any difference unless BS modifies the compiled
regex
object and for some reason needs a fresh one each time. That would be odd and I
don't see
it in the source code.
The code above has a syntax error (extra paren in the first findNext() call) -
can you
post the exact non-working code?
>
> (Also any pointers on how to get negative lookahead matching working
> would be great.
> the regex (/thread/[0-9]*)(?!\/) still matches "/thread/28606/" and
> I'd assumed it wouldn't.
Putting these expressions into Regex Demo is enlightening - the regex matches
against
"/thread/2860" - in other words the "not /" is matching against the 6.
You don't give an example of what you do want to match so it's hard to know
what a better
solution is. Some possibilities
- match anything except a digit or a slash - [^0-9/]
- match the end of the string - $
- both of the above - ([^0-9/]|$)
Kent
>
> Regards,
>
> Liam Clarke
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> Tutor maillist - Tutor@python.org
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>
>
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[Tutor] How do I fix this Invalid Mode?
Here is the latest
error:
The Currency Exchange
ProgramBy Nathan Pinno
Traceback (most recent
call last): File "D:\Python24\exchange.py", line 27, in
-toplevel- store = open('exch.txt', 'b')#loadIOError:
invalid mode: b
and the latest
code:
import picklerates
= {'can_us' : 0.80276,
'us_can' : 1.245702,
'can_euro' : 1.488707,
'euro_can' : 0.671724}
def
menu(): print "1. Change Canadian currency into
American." print "2. Change American currency into
Canadian." print "3. Change Canadian currency into
Euros." print "4. Change Euros into Canadian
currency." print "5. Update exchange
rates." print "9. Save and Exit"
def
exchange_update(): print "1. Update Canadian to US
rate." print "2. Update US to Canadian
rate." print "3. Update Canadian to Euro
rate." print "4. Update Euro to Canadian
update." print "5. Main menu"
def
menu_choice(): return int(raw_input("Which option?
"))
print "The Currency
Exchange Program"print "By Nathan Pinno"store = open('exch.txt',
'b')#loadexch = pickle.load(store)store.close()while
1: menu() menu_option =
menu_choice() if menu_option ==
1: can = float(raw_input("Canadian
$")) print "US
$",can*rates['can_us'] elif menu_option ==
2: us = float(raw_input("US
$")) print "CAN
$",us*rates['us_can'] elif menu_option ==
3: can = float(raw_input("CAN
$")) print
"Euros",can*rates['can_euro'] elif menu_option ==
4: euro =
float(raw_input("Euros")) print
"CAN $",euro*rates['euro_can'] elif menu_option ==
5: while
1:
exchange_update()
sub =
menu_choice()
if sub ==
1:
new_can = float(raw_input("New CAN-US Exchange rate:
"))
rates['can_us'] =
new_can
print "Exchange rate successfully
updated!"
elif sub ==
2:
new_us = float(raw_input("New US-CAN Exchange rate:
"))
rates['us_can'] =
new_us
print "Exchange rate successfully
updated!"
elif sub ==
3:
new_cxr = float(raw_input("New CAN-Euro Exchange rate:
"))
rates['can_euro'] =
new_cxr
print "Exchange rate successfully
updated!"
elif sub ==
4:
new_euro = float(raw_input("New Euro-CAN Exchange rate:
"))
rates['euro_can'] =
new_euro
print "Exchange rate successfully
updated!"
elif sub ==
5:
break elif menu_option ==
9: store = open("exch.txt", 'wb')
#save pickle.dump(exch,
store)
store.close() breakprint
"Goodbye."
How do I fix it this
time?
Thanks,
Nathan Pinno,
MSN Messenger: [EMAIL PROTECTED]
Yahoo! Messenger: spam_swatter31
AIM: f3mighty
ICQ: 199020705
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Re: [Tutor] How do I fix this Invalid Mode?
On Dec 17, 2005, at 2:00 PM, Nathan Pinno wrote: Here is the latest error: The Currency Exchange ProgramBy Nathan Pinno Traceback (most recent call last): File "D:\Python24\exchange.py", line 27, in -toplevel- store = open('exch.txt', 'b')#loadIOError: invalid mode: b[snip...] store = open('exch.txt', 'b')#loadexch = pickle.load(store)store.close()It looks like what you are trying to do is read exch.txt as a binary file. The problem is that 'b' by itself is not a valid mode; it's a modifier to one of the other modes (r, w or a).So to read a file in binary mode, what you want to do is: store = open('exch.txt', 'rb')Using your own code as an example, see how you implemented the save feature (option 9). That open() correctly uses the 'wb' flag to write the file in binary mode. elif menu_option == 9: store = open("exch.txt", 'wb') #save pickle.dump(exch, store) store.close() break -dan-- Black holes are where God divided by zero. -Steven Wright ___
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[Tutor] mysterious object
I'm working on Exercise 4 from Part 4 from Learning Python. I'm trying to write a function using **args. I want to create a function that adds its arguments together. Here is what I have written: def adder(**args): for x in args.keys(): print x print adder() print "---" print adder(a=5) print "---" print adder(a=5,b=6) print "---" print adder(a=5,b=6,c=7) print "---" print adder(ugly=7, good=6, bad=5) print "---" Here is my output: None --- a None --- a b None --- a c b None --- ugly bad good None --- Where do the None objects come from? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] mysterious object
Christopher Spears said unto the world upon 2005-12-17 17:42: > I'm working on Exercise 4 from Part 4 from Learning > Python. I'm trying to write a function using **args. > I want to create a function that adds its arguments > together. Here is what I have written: > > def adder(**args): > for x in args.keys(): > print x > > print adder() > print "---" > print adder(a=5) > print "---" > > > Here is my output: > > None > --- > a > None > --- Hi Christopher, all functions that terminate return a value, even if they don't have an explicit return statement. If they either have a bare "return" or no return at all, then they return None. You've put prints both in the functions and at the function calls. So, each time you've written print adder(), you've asked Python to print the return value of adder -- which is None. >>> def Noner(): return >>> print Noner() None >>> Does that clear it up? Best, Brian vdB ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] mysterious object
> def adder(**args): >for x in args.keys(): >print x A function which doesn't return a value returns None by default. > print adder() You are asking Python to print the return value of the function, which is None. As a general rule its better to do the printing outside of the function and just do the calculation bit inside, this makes the function much easier to reuse in future. HTH Alan G Author of the learn to program web tutor http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] design advice for function
I got my function to work! It takes arguments and adds them: def adder(**args): argsList = args.values() sum = argsList[0] for x in argsList[1:]: sum = sum + x return sum print adder() print "---" print adder(a=5) print "---" print adder(a=5,b=6) print "---" print adder(a=5,b=6,c=7) print "---" print adder(ugly=7, good=6, bad=5) print "---" However, if I run the above code. I get an error: Traceback (most recent call last): File "C:\Documents and Settings\Christopher Spears\My Documents\programming\PythonScripts\Part4\Ex04\adder.py", line 8, in -toplevel- print adder() File "C:\Documents and Settings\Christopher Spears\My Documents\programming\PythonScripts\Part4\Ex04\adder.py", line 3, in adder sum = argsList[0] IndexError: list index out of range This is caused by the line: print adder(). Obviously if adder() doesn't receive any arguments, it can't build the lists resulting in an IndexError. What is the best way to solve this? Should I write some syntax into the function to check for arguments? Should I just write a seperate function to check for arguments? ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
