docs: use "length" over "len" in tutorial3 python (#425)

* docs: use "length" over "len" in tutorial3  python

docs/_tutorials/tutorial_3_parse_ble_tlv_responses/tutorial.md

@@ -264,7 +264,7 @@ The snippets of code included in this section are taken from the `notification h
 
 ```python
 # Parse first 3 bytes
-len = data[0]
+length = data[0]
 command_id = data[1]
 status = data[2]
 ```
@@ -273,7 +273,7 @@ status = data[2]
 # Parse remaining four bytes
 index = 3
 params = []
-while index <= len:
+while index <= length:
     param_len = data[index]
     index += 1
     params.append(data[index : index + param_len])
@@ -1020,4 +1020,4 @@ There is additional logic required for a complete solution such as checking the
 on and storing a dict of response per UUID. At the current time, this endeavor is left for the reader. For a
 complete example of this, see the [Open GoPro Python SDK](https://gopro.github.io/OpenGoPro/python_sdk/).
 
-To learn more about queries, go to the next tutorial.
+To learn more about queries, go to the next tutorial.