File: decorators.py

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import sys

from collections import defaultdict
from os.path import splitext

import networkx as nx
from networkx.external.decorator import decorator
from networkx.utils import is_string_like

def not_implemented_for(*graph_types):
    """Decorator to mark algorithms as not implemented

    Parameters
    ----------
    graph_types : container of strings
        Entries must be one of 'directed','undirected', 'multigraph', 'graph'.

    Returns
    -------
    _require : function
        The decorated function.

    Raises
    ------
    NetworkXNotImplemnted
    If any of the packages cannot be imported

    Notes
    -----
    Multiple types are joined logically with "and".
    For "or" use multiple @not_implemented_for() lines.

    Examples
    --------
    Decorate functions like this::

       @not_implemnted_for('directed')
       def sp_function():
           pass

       @not_implemnted_for('directed','multigraph')
       def sp_np_function():
           pass
    """
    @decorator
    def _not_implemented_for(f,*args,**kwargs):
        graph = args[0]
        terms= {'directed':graph.is_directed(),
                'undirected':not graph.is_directed(),
                'multigraph':graph.is_multigraph(),
                'graph':not graph.is_multigraph()}
        match = True
        try:
            for t in graph_types:
                match = match and terms[t]
        except KeyError:
            raise KeyError('use one or more of ',
                           'directed, undirected, multigraph, graph')
        if match:
            raise nx.NetworkXNotImplemented('not implemented for %s type'%
                                            ' '.join(graph_types))
        else:
            return f(*args,**kwargs)
    return _not_implemented_for


def require(*packages):
    """Decorator to check whether specific packages can be imported.

    If a package cannot be imported, then NetworkXError is raised.
    If all packages can be imported, then the original function is called.

    Parameters
    ----------
    packages : container of strings
        Container of module names that will be imported.

    Returns
    -------
    _require : function
        The decorated function.

    Raises
    ------
    NetworkXError
    If any of the packages cannot be imported

    Examples
    --------
    Decorate functions like this::

       @require('scipy')
       def sp_function():
           import scipy
           pass

       @require('numpy','scipy')
       def sp_np_function():
           import numpy
           import scipy
           pass
    """
    @decorator
    def _require(f,*args,**kwargs):
        for package in reversed(packages):
            try:
                __import__(package)
            except:
                msg = "{0} requires {1}"
                raise nx.NetworkXError( msg.format(f.__name__, package) )
        return f(*args,**kwargs)
    return _require


def _open_gz(path, mode):
    import gzip
    return gzip.open(path,mode=mode)

def _open_bz2(path, mode):
    import bz2
    return bz2.BZ2File(path,mode=mode)

# To handle new extensions, define a function accepting a `path` and `mode`.
# Then add the extension to _dispatch_dict.
_dispatch_dict = defaultdict(lambda : open)
_dispatch_dict['.gz'] = _open_gz
_dispatch_dict['.bz2'] = _open_bz2
_dispatch_dict['.gzip'] = _open_gz


def open_file(path_arg, mode='r'):
    """Decorator to ensure clean opening and closing of files.

    Parameters
    ----------
    path_arg : int
        Location of the path argument in args.  Even if the argument is a
        named positional argument (with a default value), you must specify its
        index as a positional argument.
    mode : str
        String for opening mode.

    Returns
    -------
    _open_file : function
        Function which cleanly executes the io.

    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('path', 'w+')
       def another_function(arg, **kwargs):
           path = kwargs['path']
           pass
    """
    # 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:
    #
    # @open_file('path')
    # def some_function(arg1, arg2, path=None):
    #    if path is None:
    #        fobj = tempfile.NamedTemporaryFile(delete=False)
    #        close_fobj = True
    #    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
    #        close_fobj = False
    #
    #    try:
    #        fobj.write('blah')
    #    finally:
    #        if close_fobj:
    #            fobj.close()
    #
    # Normally, we'd want to use "with" to ensure that fobj gets closed.
    # However, recall that the decorator will make `path` a file object for
    # us, and using "with" would undesirably close that file object. Instead,
    # you use a try block, as shown above. When we exit the function, fobj will
    # be closed, if it should be, by the decorator.

    @decorator
    def _open_file(func, *args, **kwargs):

        # Note that since we have used @decorator, *args, and **kwargs have
        # already been resolved to match the function signature of func. This
        # means default values have been propagated. For example,  the function
        # func(x, y, a=1, b=2, **kwargs) if called as func(0,1,b=5,c=10) would
        # have args=(0,1,1,5) and kwargs={'c':10}.

        # First we parse the arguments of the decorator. The path_arg could
        # be an positional argument or a keyword argument.  Even if it is
        try:
            # path_arg is a required positional argument
            # This works precisely because we are using @decorator
            path = args[path_arg]
        except TypeError:
            # path_arg is a keyword argument. It is "required" in the sense
            # that it must exist, according to the decorator specification,
            # It can exist in `kwargs` by a developer specified default value
            # or it could have been explicitly set by the user.
            try:
                path = kwargs[path_arg]
            except KeyError:
                # Could not find the keyword. Thus, no default was specified
                # in the function signature and the user did not provide it.
                msg = 'Missing required keyword argument: {0}'
                raise nx.NetworkXError(msg.format(path_arg))
            else:
                is_kwarg = True
        except IndexError:
            # A "required" argument was missing. This can only happen if
            # the decorator of the function was incorrectly specified.
            # So this probably is not a user error, but a developer error.
            msg = "path_arg of open_file decorator is incorrect"
            raise nx.NetworkXError(msg)
        else:
            is_kwarg = False

        # Now we have the path_arg. There are two types of input to consider:
        #   1) string representing a path that should be opened
        #   2) an already opened file object
        if is_string_like(path):
            ext = splitext(path)[1]
            fobj = _dispatch_dict[ext](path, mode=mode)
            close_fobj = True
        elif hasattr(path, 'read'):
            # path is already a file-like object
            fobj = path
            close_fobj = False
        else:
            # could be None, in which case the algorithm will deal with it
            fobj = path
            close_fobj = False

        # Insert file object into args or kwargs.
        if is_kwarg:
            new_args = args
            kwargs[path_arg] = fobj
        else:
            # args is a tuple, so we must convert to list before modifying it.
            new_args = list(args)
            new_args[path_arg] = fobj

        # Finally, we call the original function, making sure to close the fobj.
        try:
            result = func(*new_args, **kwargs)
        finally:
            if close_fobj:
                fobj.close()

        return result

    return _open_file