vs at it
Aug 14, 2012, 12:34 PM
Post #1 of 1
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Fwd: Re: Strange behavior
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-------- Original Message --------
Subject: Re: Strange behavior
Date: Tue, 14 Aug 2012 21:32:16 +0200
From: Virgil Stokes <vs [at] it>
To: light1quark [at] gmail
On 2012-08-14 17:38, light1quark [at] gmail wrote:
> Hi, I am migrating from PHP to Python and I am slightly confused.
>
> I am making a function that takes a startingList, finds all the strings in the list that begin with 'x', removes those strings and puts them into a xOnlyList.
>
> However if you run the code you will notice only one of the strings beginning with 'x' is removed from the startingList.
> If I comment out 'startingList.remove(str);' the code runs with both strings beginning with 'x' being put in the xOnlyList.
> Using the print statement I noticed that the second string that begins with 'x' isn't even identified by the function. Why does this happen?
>
> def testFunc(startingList):
> xOnlyList = [];
> for str in startingList:
> if (str[0] == 'x'):
> print str;
> xOnlyList.append(str)
> startingList.remove(str) #this seems to be the problem
> print xOnlyList;
> print startingList
> testFunc(['xasd', 'xjkl', 'sefwr', 'dfsews'])
>
> #Thanks for your help!
You might find the following useful:
def testFunc(startingList):
xOnlyList = []; j = -1
for xl in startingList:
if (xl[0] == 'x'):
xOnlyList.append(xl)
else:
j += 1
startingList[j] = xl
if j == -1:
startingList = []
else:
del startingList[j:-1]
return(xOnlyList)
testList1 = ['xasd', 'xjkl', 'sefwr', 'dfsews']
testList2 = ['xasd', 'xjkl', 'xsefwr', 'xdfsews']
testList3 = ['xasd', 'jkl', 'sefwr', 'dfsews']
testList4 = ['asd', 'jkl', 'sefwr', 'dfsews']
xOnlyList = testFunc(testList1)
print 'xOnlyList = ',xOnlyList
print 'testList = ',testList1
xOnlyList = testFunc(testList2)
print 'xOnlyList = ',xOnlyList
print 'testList = ',testList2
xOnlyList = testFunc(testList3)
print 'xOnlyList = ',xOnlyList
print 'testList = ',testList3
xOnlyList = testFunc(testList4)
print 'xOnlyList = ',xOnlyList
print 'testList = ',testList4
And here is another version using list comprehension that I prefer
testList1 = ['xasd', 'xjkl', 'sefwr', 'dfsews']
testList2 = ['xasd', 'xjkl', 'xsefwr', 'xdfsews']
testList3 = ['xasd', 'jkl', 'sefwr', 'dfsews']
testList4 = ['asd', 'jkl', 'sefwr', 'dfsews']
def testFunc2(startingList):
return([x for x in startingList if x[0] == 'x'], [x for x in
startingList if x[0] != 'x'])
xOnlyList,testList = testFunc2(testList1)
print xOnlyList
print testList
xOnlyList,testList = testFunc2(testList2)
print xOnlyList
print testList
xOnlyList,testList = testFunc2(testList3)
print xOnlyList
print testList
xOnlyList,testList = testFunc2(testList4)
print xOnlyList
print testList
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