Self-contained checkpoint --resume (#8839)

* Single checkpoint resume

* Update train.py

* Add hyp

* Add hyp

* Add hyp

* FIX

* avoid resume on url data

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* avoid resume on url data

* avoid resume on url data

* Update

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

utils/downloads.py

@@ -16,12 +16,14 @@ import requests
 import torch
 
 
-def is_url(url):
+def is_url(url, check_online=True):
     # Check if online file exists
     try:
-        r = urllib.request.urlopen(url)  # response
-        return r.getcode() == 200
-    except urllib.request.HTTPError:
+        url = str(url)
+        result = urllib.parse.urlparse(url)
+        assert all([result.scheme, result.netloc, result.path])  # check if is url
+        return (urllib.request.urlopen(url).getcode() == 200) if check_online else True  # check if exists online
+    except (AssertionError, urllib.request.HTTPError):
         return False