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Subject: Re: Strange behaviour with a for loop.
From: Sean Murphy <mhysnm1964@gmail.com>
In-Reply-To: <la86n0$sdk$1@ger.gmane.org>
Date: Sat, 4 Jan 2014 16:54:42 +1100
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References: <4DC5A4FC-CCAF-446B-B41C-23E52C2389B6@icloud.com> <la86n0$sdk$1@ger.gmane.org>
To: Mark Lawrence <breamoreboy@yahoo.co.uk>
Cc: python-list@python.org
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Xref: csiph.com comp.lang.python:63116

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 =3D "test.txt"
print a[3]

result is:

't


print a[3:1]

Nothing is printed.=20

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=20


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=20



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.
>>=20
>> This is a newly question. But I wish to understand why the below code =
is providing different results.
>>=20
>> import os, sys
>>=20
>>=20
>> if len(sys.argv) > 2:
>>   filenames =3D sys.argv[1:]
>> else
>>   print ("no parameters provided\n")
>>   sys.edit()
>>=20
>> for filename in filenames:
>>   print ("filename is: %s\n" %filename)
>>=20
>> The above code will return results like:
>>=20
>> filename is test.txt
>>=20
>> If I modify the above script slightly as shown below, I get a =
completely different result.
>>=20
>> if len(sys.argv) > 2:
>>   filenames =3D sys.argv[1]
>> else
>>   print ("no parameters provided\n")
>>   sys.exit()
>>=20
>> for filename in filenames:
>>   print ("filename is:  %s\n" % filename)
>>=20
>> 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.
>>=20
>> 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).
>>=20
>>=20
>> Sean
>> filename is: t
>> filename
>>=20
>=20
> 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 :)
>=20
> --=20
> My fellow Pythonistas, ask not what our language can do for you, ask =
what you can do for our language.
>=20
> Mark Lawrence
>=20
> --=20
> https://mail.python.org/mailman/listinfo/python-list