From bbf70bf21c4a477a4575d33c337cfe453485f45e Mon Sep 17 00:00:00 2001
From: Mike Liu <mike.liu.dev@gmail.com>
Date: Mon, 11 Jun 2018 12:28:11 -0400
Subject: [PATCH] Fix using mutable default arguments.

According to
http://docs.python-guide.org/en/latest/writing/gotchas/#mutable-default-arguments
using mutable default arguments is not a good practice since it doesn't
perform intuitively. For example lists and dictionaries as default
arguments are initialized ONCE instead of on each invocation of the
function.
---
 moto/ssm/models.py | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/moto/ssm/models.py b/moto/ssm/models.py
index 688cffcd5..f839e2e14 100644
--- a/moto/ssm/models.py
+++ b/moto/ssm/models.py
@@ -64,10 +64,22 @@ MAX_TIMEOUT_SECONDS = 3600
 
 class Command(BaseModel):
     def __init__(self, comment='', document_name='', timeout_seconds=MAX_TIMEOUT_SECONDS,
-            instance_ids=[], max_concurrency='', max_errors='',
-            notification_config={}, output_s3_bucket_name='',
-            output_s3_key_prefix='', output_s3_region='', parameters={},
-            service_role_arn='', targets=[]):
+            instance_ids=None, max_concurrency='', max_errors='',
+            notification_config=None, output_s3_bucket_name='',
+            output_s3_key_prefix='', output_s3_region='', parameters=None,
+            service_role_arn='', targets=None):
+
+        if instance_ids is None:
+            instance_ids = []
+
+        if notification_config is None:
+            notification_config = {}
+
+        if parameters is None:
+            parameters = {}
+
+        if targets is None:
+            targets = []
 
         self.error_count = 0
         self.completed_count = len(instance_ids)