diff --git a/demo_code.py b/demo_code.py
index 275fda452..76ac5d837 100644
--- a/demo_code.py
+++ b/demo_code.py
@@ -1,10 +1,10 @@
-import random
-import sys as sys
+import collections
 import os
-import subprocess
-import ssl
 import pprint
-import collections
+import random
+import ssl
+import subprocess
+import sys as sys
 
 import this
 
@@ -40,8 +40,10 @@ def limits(self):
         a = 2
         return self.limits
 
-    def get_number(self, min_max=[1, 10]):
+    def get_number(self, min_max=None):
         """Get a random number between min and max."""
+        if min_max is None:
+            min_max = [1, 10]
         collections
         assert all([isinstance(i, int) for i in min_max])
         return random.randint(*min_max)
@@ -58,7 +60,9 @@ def __getattr__(self, key):
         return key
 
 
-def main(options: dict = {}) -> str:
+def main(options: dict = None) -> str:
+    if options is None:
+        options = {}
     if "run" in options:
         value = options["run"]
     else:
@@ -75,7 +79,9 @@ def main(options: dict = {}) -> str:
     f.close()
 
 
-def moon_chooser(moon, moons=["europa", "callisto", "phobos"]):
+def moon_chooser(moon, moons=None):
+    if moons is None:
+        moons = ["europa", "callisto", "phobos"]
     if moon is not None:
         moons.append(moon)
 
diff --git a/foo.py b/foo.py
index 40df53dbf..6df8a99b7 100644
--- a/foo.py
+++ b/foo.py
@@ -1,6 +1,7 @@
-import os
 import logging
-nums = [ i for i in range(10)]
+import os
+
+nums = [i for i in range(10)]
 
 a = 1
 b = 2
@@ -9,35 +10,50 @@
 breakpoint()
 print(b, nums)
 
-def baz(a=[]):
-  return 0
 
-def aaa(a=[]):
-  return 1
+def baz(a=None):
+    if a is None:
+        a = []
+    return 0
+
 
+def aaa(a=None):
+    if a is None:
+        a = []
+    return 1
+
+
+def foo(b=None):
+    if b is None:
+        b = []
+    return 1
 
-def foo(b=[]):
-  return 1
 
 def bar(a):
-  return 1
+    return 1
+
 
 import os
+
 filename = os.tmpnam()
-with open(filename,  'w') as f:
-  pass
+with open(filename, "w") as f:
+    pass
+
+
+def boom(a=None):
+    if a is None:
+        a = []
+    breakpoint()
+    filename = os.tmpnam()
+    breakpoint()
+    return filename
 
-def boom(a=[]):
-  breakpoint()
-  filename =  os.tmpnam()
-  breakpoint()
-  return filename
 
 def another_test_method():
-  f = open("/tmp/.deepsource.toml",  "r")
-  f.write("config file.")
-  f.close()
-  print('abc')
-  
-filename = os.tmpnam()
+    f = open("/tmp/.deepsource.toml", "r")
+    f.write("config file.")
+    f.close()
+    print("abc")
+
 
+filename = os.tmpnam()