Fix: add utility to check whether a string is a filepath

src/awkward/_util.py

@@ -5,6 +5,7 @@
 import re
 import sys
 import os
+import os.path
 import warnings
 import itertools
 import numbers
@@ -41,6 +42,13 @@
 kMaxLevels = 48
 
 
+def is_file_path(x):
+    try:
+        return os.path.isfile(x)
+    except ValueError:
+        return False
+
+
 def isint(x):
     """
     Returns True if and only if ``x`` is an integer (including NumPy, not

src/awkward/operations/convert.py

@@ -1075,7 +1075,7 @@ def from_json(
 
     is_path, source = ak._util.regularize_path(source)
 
-    if os.path.isfile(source):
+    if ak._util.is_file_path(source):
         layout = ak._ext.fromjsonfile(
             source,
             nan_string=nan_string,

tests/test_1084-from-json-win-path.py

@@ -0,0 +1,23 @@
+# BSD 3-Clause License; see https://github.com/scikit-hep/awkward-1.0/blob/main/LICENSE
+from __future__ import absolute_import
+
+import pytest  # noqa: F401
+import numpy as np  # noqa: F401
+import awkward as ak  # noqa: F401
+
+
+@pytest.mark.skipif(not ak._util.win, reason="need Windows to test this case")
+def test():
+    if not ak._util.py27:
+        # Python 2.7 has differently named urllib libraries
+        import urllib.request
+        import urllib.error
+
+        url = "https://raw.githubusercontent.com/Chicago/osd-bike-routes/5f556dc/data/Bikeroutes.geojson"
+        try:
+            bikeroutes_json = urllib.request.urlopen(url).read()
+        except urllib.error.URLError:
+            pytest.skip(msg="couldn't download sample dataset")
+
+        # This shouldn't fail (see #1084)
+        ak.from_json(bikeroutes_json)