allow for configuring default_dir (#3277)

* allow for configuring default_dir

* allow for using DGLDEFAULTDIR environment variable

* Update env_var.rst
Co-authored-by: Quan (Andy) Gan <coin2028@hotmail.com>
Co-authored-by: Jinjing Zhou <VoVAllen@users.noreply.github.com>

docs/source/env_var.rst

 Environment Variables
 =====================
 
+Global Configurations
+---------------------
+* ``DGLDEFAULTDIR``:
+    * Values: String (default=``"${HOME}/.dgl"``)
+    * The directory to save the DGL configuration files.
+
 Backend Options
 ---------------
 * ``DGLBACKEND``:
@@ -20,7 +26,7 @@ Data Repository
         * 'https://data.dgl.ai/': DGL repo for Global Region.
         * 'https://dgl-data.s3.cn-north-1.amazonaws.com.cn/': DGL repo for Mainland China
 * ``DGL_DOWNLOAD_DIR``:
-    * Values: String (default="${HOME}/.dgl")
+    * Values: String (default=``"${HOME}/.dgl"``)
     * The local directory to cache the downloaded data.
 
 Intel CPU Performance Options

python/dgl/backend/__init__.py

@@ -74,7 +74,12 @@ def load_backend(mod_name):
                 setattr(thismod, api, _gen_missing_api(api, mod_name))
 
 def get_preferred_backend():
-    config_path = os.path.join(os.path.expanduser('~'), '.dgl', 'config.json')
+    default_dir = None
+    if "DGLDEFAULTDIR" in os.environ:
+        default_dir = os.getenv('DGLDEFAULTDIR')
+    else:
+        default_dir = os.path.join(os.path.expanduser('~'), '.dgl')
+    config_path = os.path.join(default_dir, 'config.json')
     backend_name = None
     if "DGLBACKEND" in os.environ:
         backend_name = os.getenv('DGLBACKEND')
@@ -88,7 +93,7 @@ def get_preferred_backend():
     else:
         print("DGL backend not selected or invalid.  "
               "Assuming PyTorch for now.", file=sys.stderr)
-        set_default_backend('pytorch')
+        set_default_backend(default_dir, 'pytorch')
         return 'pytorch'
 
 

python/dgl/backend/set_default_backend.py

@@ -2,8 +2,7 @@ import argparse
 import os
 import json
 
-def set_default_backend(backend_name):
-    default_dir = os.path.join(os.path.expanduser('~'), '.dgl')
+def set_default_backend(default_dir, backend_name):
     if not os.path.exists(default_dir):
         os.makedirs(default_dir)
     config_path = os.path.join(default_dir, 'config.json')
@@ -16,7 +15,8 @@ def set_default_backend(backend_name):
 
 if __name__ == "__main__":
     parser = argparse.ArgumentParser()
+    parser.add_argument("default_dir", type=str, default=os.path.join(os.path.expanduser('~'), '.dgl'))
     parser.add_argument("backend", nargs=1, type=str, choices=[
                         'pytorch', 'tensorflow', 'mxnet'], help="Set default backend")
     args = parser.parse_args()
-    set_default_backend(args.backend[0])
+    set_default_backend(args.default_dir, args.backend[0])