lazy-load boto3 to save ~400ms startup time (#12914)

* lazy-load boto3 to save ~400ms startup time

Co-authored-by: Ken Odegard <kodegard@anaconda.com>

---------

Co-authored-by: Ken Odegard <kodegard@anaconda.com>

conda/gateways/connection/adapters/s3.py

@@ -5,18 +5,23 @@
 from logging import LoggerAdapter, getLogger
 from tempfile import SpooledTemporaryFile
 
-have_boto3 = have_boto = False
-try:
-    import boto3
+boto3 = boto = None
 
-    have_boto3 = True
-except ImportError:
-    try:
-        import boto
 
-        have_boto = True
+def _load_boto3():
+    """
+    Import boto3 on demand only to save startup time.
+    """
+    global boto3, boto
+
+    try:
+        import boto3
     except ImportError:
-        pass
+        try:
+            import boto
+        except ImportError:
+            pass
+
 
 from ....common.compat import ensure_binary
 from ....common.url import url_to_s3_info
@@ -36,9 +41,13 @@ def send(
         resp = Response()
         resp.status_code = 200
         resp.url = request.url
-        if have_boto3:
+
+        if not (boto3 or boto):
+            _load_boto3()
+
+        if boto3:
             return self._send_boto3(boto3, resp, request)
-        elif have_boto:
+        elif boto:
             return self._send_boto(boto, resp, request)
         else:
             stderrlog.info(

news/lazy-load-boto3

@@ -0,0 +1,19 @@
+### Enhancements
+
+* Import boto3 only when s3 channels are used, saving startup time. (#12914)
+
+### Bug fixes
+
+* <news item>
+
+### Deprecations
+
+* <news item>
+
+### Docs
+
+* <news item>
+
+### Other
+
+* <news item>