adds scope

learning_python3.md

@@ -584,6 +584,73 @@ bake_cake("banana")
 
 ## Variable scope
 
+Variable scope might sounds complicated but with some examples you'll understand it in no time.
+Remember variables are like unique *post-its*?
+Well, variable scope is like having multiple colors for your post-its.
+A yellow post-it with `name` on it is not the same as a red one with `name` on it so they can both reference **different** objects.
+Scope is **where** the colors change, and this is done automatically for you in python.
+It's an inherent feature of the language but the concept of scope is not unique to python, you'll find it in most modern languages.
+Now, some examples.
+
+```python3
+total = 9000
+
+def function_scope(argument_one, argument_two):
+    print("inside the function", argument_one, argument_two)
+    total = argument_one + argument_two
+    print("inside the function", total)
+
+
+function_scope(300, 400)
+print("outside the function", total)
+```
+
+Here `total` outside of the function references a different object from the `total` inside of the function.
+Python is very *nice* and will try to fix some common mistakes or oversights by itself.
+For example.
+
+```python3
+name = "Wouter"
+
+def function_scope():
+    print("inside the function", name)
+
+
+function_scope()
+print("outside the function", name)
+```
+
+But we can not **modify** the referenced object from **inside** the function.
+This will give an `UnboundLocalError: local variable 'name' referenced before assignment` error
+
+```python3
+name = "Wouter"
+
+def function_scope():
+    print("inside the function", name)
+	name = "Alice"
+
+
+function_scope()
+print("outside the function", name)
+```
+
+There is however a handy **keyword** we can use to explicitly reference variables from the outermost scope.
+This is done as follows with the `global` keyword.
+
+```python3
+name = "Wouter"
+
+def function_scope():
+	global name
+    print("inside the function", name)
+	name = "Alice"
+
+
+function_scope()
+print("outside the function", name)
+```
+
 ## Functions that *return* something
 
 TODO basic math functions