help with class

[Arnaud Delobelle]

tekion <tekion at gmail.com> writes:

> Hello,
> I am playing with class.  Below is the code snippet:
> #!/usr/bin/python
>       2
>       3 class test_class:
>       4    #import gzip
>       5    def __init__(self,file):
>       6       self.file = file
>       7    def open_file(self):
>       8       try:
>       9          print "file: %s" % self.file
>      10          self.xml_file = gzip.GzipFile(self.file,'r')
>      11       except:
>      12          print "an exception has occured"
>      13       for line in self.xml_file:
>      14          print "line: %s" % line
>      15       self.xml_file.close()
>      16
>      17
>      18 if __name__ == '__main__':
>      19    import gzip
>      20    import sys
>      21    t = test_class( sys.argv[1] )
>      22    t.open_file()
>
> My question are:
> 1.  Why do I need to use "import gzip" on main section to get it the
> script to work?  I would assume you need the import of gzip in the
> class section.

This is how Python works.  Here is the relevant extract from the
Reference Manual:

    A scope defines the visibility of a name within a block. If a local
    variable is defined in a block, its scope includes that block. If
    the definition occurs in a function block, the scope extends to any
    blocks contained within the defining one, unless a contained block
    introduces a different binding for the name. The scope of names
    defined in a class block is limited to the class block; it does not
    extend to the code blocks of methods – this includes generator
    expressions since they are implemented using a function scope.

(Quoted from http://docs.python.org/reference/executionmodel.html)

> 2.  What is the proper way of using module in a class you are creating?

import it into the global namespace of the module in which you are
defining your class.

-- 
Arnaud