mod_list+add_trait.py

In [13]: from enthought.traits.api import *

In [14]: class A(HasTraits):
   ....:     pass
   ....: 

In [16]: a = A()

In [17]: a.add_trait('foo',MultiPath(File(exists=True)))

In [18]: a.foo = 'fsl_tutorial.py'

In [19]: a.trait_names()
Out[19]: ['trait_added', 'trait_modified']

In [20]: a.goo = 'fsl_tutorial.py'

In [22]: a.trait_names()
Out[22]: ['trait_added', 'goo', 'trait_modified']

In [24]: a.foo = 'fsl_tutorial.p'
---------------------------------------------------------------------------
TraitError                                Traceback (most recent call last)

TraitError: Each element of the 'foo' trait of an A instance must be a file name, but a value of 'fsl_tutorial.p' <type 'str'> was specified.

mod_list.py

class MultiPath(List):
    """ Implements a user friendly traits that accepts one or more
    paths to files or directories and return a single string whenever 
    possible (when it was set to a single value or a list of length 1). 

    >>> class A(HasTraits):
    ...     foo = MultiPath(File(exists=False))
    >>> a = A()
    
    >>> a.foo = '/software/temp/foo.txt'
    >>> a.foo
    '/software/temp/foo.txt'

    >>> a.foo = ['/software/temp/foo.txt']
    >>> a.foo
    '/software/temp/foo.txt'

    >>> a.foo = ['/software/temp/foo.txt', '/software/temp/goo.txt']
    >>> a.foo
    ['/software/temp/foo.txt', '/software/temp/goo.txt']
    
    """
    
    def validate(self, object, name, value):
        if not isdefined(value) or (isinstance(value, list) and len(value)==0):
            return _Undefined()
        newvalue = value
        if not isinstance(value, list):
            newvalue = [value]
        value = super(MultiPath, self).validate(object, name, newvalue)
        
        if len(value) > 0:
            return value

        self.error( object, name, value )
       
    def get(self, object, name):
        value = self.get_value(object, name)
        if len(value) == 0:
            return Undefined
        elif len(value)==1:
            return value[0]
        else:
            return value

    def set(self, object, name, value):
        self.set_value(object, name, value)