[Lint] Pylint (#330)

* fix lint for graph_index.py

* pylint for base.py

* pylint for batched_graph.py

* pylint for frame.py; simplify and fix bugs in frame when index is slice type

* pylint for graph.py

* pylint for immutable_graph_index.py

* pylint for init.py

* pylint for rest files in root package

* pylint for _ffi package

* pylint for function package

* pylint for runtime package

* pylint for runtime.ir package

* add pylint to ci

* fix mx tests

* fix lint errors

* fix ci

* fix as requested

* fix lint

python/dgl/__init__.py

@@ -1,5 +1,4 @@
-# One has to manually import dgl.data; fixes #125
-#from . import data
+"""DGL root package."""
 from . import function
 from . import nn
 from . import contrib
@@ -12,7 +11,6 @@
 from .backend import load_backend
 from .batched_graph import *
 from .graph import DGLGraph
-from .subgraph import DGLSubGraph
 from .traversal import *
 from .propagate import *
 from .udf import NodeBatch, EdgeBatch

python/dgl/_api_internal.py

@@ -0,0 +1 @@
+"""Namespace for internal apis."""

python/dgl/_ffi/base.py

@@ -26,8 +26,7 @@
 
 class DGLError(Exception):
     """Error thrown by DGL function"""
-    pass
-
+    pass  # pylint: disable=unnecessary-pass
 
 def _load_lib():
     """Load libary by searching possible path."""

python/dgl/_ffi/function.py

@@ -51,7 +51,7 @@ class Function(_FunctionBase):
     dgl.register_func: How to register global function.
     dgl.get_global_func: How to get global function.
     """
-    pass
+    pass  # pylint: disable=unnecessary-pass
 
 
 class ModuleBase(object):

python/dgl/_ffi/runtime_ctypes.py

@@ -1,5 +1,5 @@
 """Common runtime ctypes."""
-# pylint: disable=invalid-name
+# pylint: disable=invalid-name, super-init-not-called
 from __future__ import absolute_import
 
 import ctypes

python/dgl/backend/mxnet/immutable_graph_index.py

@@ -349,6 +349,31 @@ def from_coo_matrix(self, out_coo):
         self.__init__(mx.nd.sparse.csr_matrix((edge_ids, (dst, src)), shape=(size, size)).astype(np.int64),
                 mx.nd.sparse.csr_matrix((edge_ids, (src, dst)), shape=(size, size)).astype(np.int64))
 
+    def from_edge_list(self, elist):
+        """Convert from an edge list.
+
+        Paramters
+        ---------
+        elist : list
+            List of (u, v) edge tuple.
+        """
+        src, dst = zip(*elist)
+        src = np.array(src)
+        dst = np.array(dst)
+        num_nodes = max(src.max(), dst.max()) + 1
+        min_nodes = min(src.min(), dst.min())
+        if min_nodes != 0:
+            raise DGLError('Invalid edge list. Nodes must start from 0.')
+        edge_ids = mx.nd.arange(0, len(src), step=1, repeat=1, dtype=np.int32)
+        src = mx.nd.array(src, dtype=np.int64)
+        dst = mx.nd.array(dst, dtype=np.int64)
+        # TODO we can't generate a csr_matrix with np.int64 directly.
+        in_csr = mx.nd.sparse.csr_matrix((edge_ids, (dst, src)),
+                                         shape=(num_nodes, num_nodes)).astype(np.int64)
+        out_csr = mx.nd.sparse.csr_matrix((edge_ids, (src, dst)),
+                                          shape=(num_nodes, num_nodes)).astype(np.int64)
+        self.__init__(in_csr, out_csr)
+
 def create_immutable_graph_index(in_csr=None, out_csr=None):
     """ Create an empty backend-specific immutable graph index.
 

python/dgl/base.py

@@ -3,12 +3,15 @@
 
 import warnings
 
-from ._ffi.base import DGLError
+from ._ffi.base import DGLError  # pylint: disable=unused-import
 
-# A special argument for selecting all nodes/edges.
+# A special symbol for selecting all nodes or edges.
 ALL = "__ALL__"
 
 def is_all(arg):
+    """Return true if the argument is a special symbol for all nodes or edges."""
     return isinstance(arg, str) and arg == ALL
 
-dgl_warning = warnings.warn
+def dgl_warning(msg):
+    """Print out warning messages."""
+    warnings.warn(msg)