Taxi-v3 docs fix (openai#2360)

* Changed the docstring of Taxi env * Changed the docs of Taxi env
Denkiyohou · Aug 26, 2021 · 4e38147 · 4e38147
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diff --git a/docs/toy_text/taxi.md b/docs/toy_text/taxi.md
@@ -41,6 +41,10 @@ Observations:
 
 There are 500 discrete states since there are 25 taxi positions, 5 possible locations of the passenger (including the case when the passenger is in the taxi), and 4 destination locations.
 
+Note that there are 400 states that can actually be reached during an episode. The missing states correspond to situations in which the passenger is at the same location as their destination, as this typically signals the end of an episode.
+Four additional states can be observed right after a successful episodes, when both the passenger and the taxi are at the destination.
+This gives a total of 404 reachable discrete states.
+
 Passenger locations:
 - 0: R(ed)
 - 1: G(reen)

diff --git a/gym/envs/toy_text/taxi.py b/gym/envs/toy_text/taxi.py
@@ -27,6 +27,9 @@ class TaxiEnv(discrete.DiscreteEnv):
 
     Observations:
     There are 500 discrete states since there are 25 taxi positions, 5 possible locations of the passenger (including the case when the passenger is in the taxi), and 4 destination locations.
+    Note that there are 400 states that can actually be reached during an episode. The missing states correspond to situations in which the passenger is at the same location as their destination, as this typically signals the end of an episode.
+    Four additional states can be observed right after a successful episodes, when both the passenger and the taxi are at the destination.
+    This gives a total of 404 reachable discrete states.
 
     Passenger locations:
     - 0: R(ed)