open_file

open_file(path_arg, mode='r')

Decorator to ensure clean opening and closing of files.

Parameters

path_argstring or int

Name or index of the argument that is a path.

modestr

String for opening mode.

Returns

_open_filefunction

Function which cleanly executes the io.

Notes

Note that this decorator solves the problem when a path argument is specified as a string, but it does not handle the situation when the function wants to accept a default of None (and then handle it).

Here is an example of how to handle this case:

@open_file("path")
def some_function(arg1, arg2, path=None):
   if path is None:
       fobj = tempfile.NamedTemporaryFile(delete=False)
   else:
       # `path` could have been a string or file object or something
       # similar. In any event, the decorator has given us a file object
       # and it will close it for us, if it should.
       fobj = path

   try:
       fobj.write("blah")
   finally:
       if path is None:
           fobj.close()

Normally, we’d want to use “with” to ensure that fobj gets closed. However, the decorator will make path a file object for us, and using “with” would undesirably close that file object. Instead, we use a try block, as shown above. When we exit the function, fobj will be closed, if it should be, by the decorator.

Examples

Decorate functions like this:

@open_file(0,"r")
def read_function(pathname):
    pass

@open_file(1,"w")
def write_function(G, pathname):
    pass

@open_file(1,"w")
def write_function(G, pathname="graph.dot"):
    pass

@open_file("pathname","w")
def write_function(G, pathname="graph.dot"):
    pass

@open_file("path", "w+")
def another_function(arg, **kwargs):
    path = kwargs["path"]
    pass