Some typo corrections.

ipynb/pres07_data_struct.ipynb

@@ -6,11 +6,11 @@
 
 Pierre Augier (LEGI), Cyrille Bonamy (LEGI), Eric Maldonado (Irstea), Franck Thollard (ISTerre), Christophe Picard (LJK), Loïc Huder (ISTerre)
 
 # [Data structures](https://docs.python.org/3/tutorial/datastructures.html)
 
-4 built-in containers: list, tuple, set and dict...
+4 built-in containers: list, tuple, set and dict.
 
 For more containers: see [collections](https://docs.python.org/3/library/collections.html)...
 
 %% Cell type:markdown id: tags:
 
@@ -39,11 +39,11 @@
 
 %% Cell type:markdown id: tags:
 
 ### list: mutable sequence
 
-The builtin function `dir` returns a list of name of the attributes. For a list, these attributes are python system attributes (with double-underscores) and 11 public methods:
+The built-in function `dir` returns a list of name of the attributes. For a list, these attributes are python system attributes (with double-underscores) and 11 public methods:
 
 
 %% Cell type:code id: tags:
 
 ``` python
@@ -169,12 +169,12 @@
 t0 = ()
 t1 = tuple()
 assert t0 == t1
 
 # not empty tuple
-t2 = (1, 2, 'a')  # with the parenthesis
-t2 = 1, 2, 'a'    # it also works without parenthesis
+t2 = (1, 2, 'a')  # with the parentheses
+t2 = 1, 2, 'a'    # it also works without parentheses
 t3 = tuple(l3)  # from a list
 ```
 
 %% Cell type:code id: tags:
 
@@ -314,17 +314,17 @@
 
     12
 
 %% Cell type:markdown id: tags:
 
-## Complity :
+## Complexity :
 
   - line 1: n insertions --> O(n)
-  - line 2 : n insertions --> O(n)
+  - line 2: n insertions --> O(n)
   - line 3: one traversal O(n), with one lookup at each time (O(1) -> O(n) 
   
-  -> Complixity of the whole algorithm : O(n)
+  -> Complexity of the whole algorithm : O(n)
   
 # Complexity of the "sum" solution : 
    - One traversal for the computation of the sum O(n) with sum at each step O(1) -> O(n) 
 
 %% Cell type:markdown id: tags:
@@ -393,11 +393,13 @@
 
     'value1'
 
 %% Cell type:markdown id: tags:
 
-But warning, `dict` are not ordered (since they are based on a hashtable)!
+**Warning:** In general, `dict` are not ordered (since they are based on a hashtable)! 
+
+However, since Python 3.6, the implementation changed so that `dict` now keep the order of insertion of keys.
 
 %% Cell type:markdown id: tags:
 
 ### `dict`: public methods
 
@@ -429,12 +431,11 @@
 %% Cell type:code id: tags:
 
 ``` python
 # loop with items
 for key, value in d.items():
-    if isinstance(key, str): 
-        print(key, value)
+    print(key, value)
 ```
 
 %% Cell type:code id: tags:
 
 ``` python