a simple 'for' question

Tim Roberts timr at probo.com
Thu Jul 10 09:34:06 CEST 2008

Ethan Furman <ethan at stoneleaf.us> wrote:

>Ben Keshet wrote:
>> it didn't help.  it reads the pathway "as is" (see errors for both 
>> tries).  It looks like it had the write pathway the first time, but 
>> could not find it because it searched in the path/way instead of in the 
>> path\way.  thanks for trying.
>The form of slash ('\' vs '/') is irrelevant to Python.  At least on 
>> folders= ['1','2','3']
>> for x in folders:
>>     print x     # print the current folder
>>     filename='Folder/%s/myfile.txt' %[x]
>                                        ^- brackets not needed

More than that, the brackets are CAUSING this problem.  The "%" formatting
operator expects to find either a single item, or a tuple containing
multiple items.  It does NOT look for a generic iterator.  In this case,
the %s will use the whole list as its parameter.  Python converts the list
to string, and the string representation of that one-item list is ['1'].

>>     f=open(filename,'r')
>> gives: IOError: [Errno 2] No such file or directory: 
>> "Folder/['1']/myfile.txt"

Just like that.

>As far as the Python question of string substitution, "%s" % var is an 
>appropriate way.

Tim Roberts, timr at probo.com
Providenza & Boekelheide, Inc.

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