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Re: Strange behaviour with a for loop.

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Hi everyone.

Worked out what I was doing wrong with the string splicing. The offset number was lower then the index number, so it was failing. E.G:




On 04/01/2014, at 4:54 PM, Sean Murphy <mhysnm1964@gmail.com> wrote:

> Thanks everyone.
> 
> Mark thanks for the correction on the ':'. Since I didn't cut and copy, rather typed it out. Errors crept in. :-)
> 
> another question in relation to slicing strings. If you want to get a single character, just using the index position will get it. If I use the following, shouldn't it also work? when I use Python 3.3, it didn't provide anything.
> 
> a = "test.txt"
> print a[3]
> 
print a[4:1] <--- index is 4 and offset is one. This is invalid.

So I suspect the offset number still starts at the beginning of the string and counts forward or another way to look at it you are slicing from element x to element y. If element y is less then element x, return nothing. Does this make sense?

I should have used:

print a[4:6])

to get:

t.t 

The 2nd part of my original question still stands. I will expand upon this a bit more to give more context. I want to print from the beginning of the paragraph to the end. Each paragraph ends with "\n\n\n". 

If I use "\n\n\n" in lines this does return true for the string. But I don't have a starting position and ending position. The list method which I mention before can be sliced by going back one element.

Any suggestion on this would be welcomed. I want to achieve this using standard core python objects/methods.

Sean 
> result is:
> 
> 't
> 
> 
> print a[3:1]
> 
> Nothing is printed. 
> 
> print a[3:2]
> 
> 
> Nothing is printed.
> 
> print a[3:-1]
> 
> t.tx is printed.
> 
> 
> Why doesn't the positive number of characters to be splice return anything while the negative value does?
> 
> sorry about these basic questions. I do like the splice feature within Python. Also what is the best method of testing for a blank string?
> 
> end of paragraph line 1 
> 
> 
> new paragraph of line 1.
> 
> 
> The above example text is what I want to test for. I am planning to either load the whole file in as a single chunk of memory using fp.read() or store it into an array by using fp.readlines(). The first option I see being useful because you can create a regular expression to test for multiple '\n'. While in an array (list) I would have to test for a blank line which I assume would be "".
> 
> Any suggestions on this would be welcomed.
> 
> Sean 
> 
> 
> 
> print a[
> 
> On 04/01/2014, at 4:38 PM, Mark Lawrence <breamoreboy@yahoo.co.uk> wrote:
> 
>> On 04/01/2014 04:03, Sean Murphy wrote:
>>> Hello all.
>>> 
>>> This is a newly question. But I wish to understand why the below code is providing different results.
>>> 
>>> import os, sys
>>> 
>>> 
>>> if len(sys.argv) > 2:
>>>  filenames = sys.argv[1:]
>>> else
>>>  print ("no parameters provided\n")
>>>  sys.edit()
>>> 
>>> for filename in filenames:
>>>  print ("filename is: %s\n" %filename)
>>> 
>>> The above code will return results like:
>>> 
>>> filename is test.txt
>>> 
>>> If I modify the above script slightly as shown below, I get a completely different result.
>>> 
>>> if len(sys.argv) > 2:
>>>  filenames = sys.argv[1]
>>> else
>>>  print ("no parameters provided\n")
>>>  sys.exit()
>>> 
>>> for filename in filenames:
>>>  print ("filename is:  %s\n" % filename)
>>> 
>>> The result is the filename is spelled out a character at a time. The bit I am missing is something to do with splicing or referencing in Python.
>>> 
>>> Why am I getting different results? In other languages I would have got the whole content of the element when using the index of the array (list).
>>> 
>>> 
>>> Sean
>>> filename is: t
>>> filename
>>> 
>> 
>> As you've already had answers I'd like to point out that your test for len(sys.argv) is wrong, else is missing a colon and sys.edit() is very unlikely to work :)
>> 
>> -- 
>> My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language.
>> 
>> Mark Lawrence
>> 
>> -- 
>> https://mail.python.org/mailman/listinfo/python-list
> 

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Re: Strange behaviour with a for loop. Sean Murphy <mhysnm1964@gmail.com> - 2014-01-04 17:32 +1100
  Re: Strange behaviour with a for loop. Larry Hudson <orgnut@yahoo.com> - 2014-01-04 14:20 -0800

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