diff --git a/source/Data_Types.rst b/source/Data_Types.rst
index e36ec6bbd1b5ed003a0a16c4726ad95b35be5215..cae429a2bc93aa7f579dd909a4b1dc82d548acfd 100644
--- a/source/Data_Types.rst
+++ b/source/Data_Types.rst
@@ -330,39 +330,6 @@ Exercise
 .. #. Using the shorter string  ``s = 'gaattc'`` draw what happens in memory when you reverse ``s``.
 
 
-Exercise
---------
-
-| The ``il2_human`` sequence contains 4 cysteins (C) in positions 9, 78, 125, 145.
-| We want to generate the sequence of a mutant where the cysteins 78 and 125 are replaced by serins (S)
-| Write the pseudocode, before proposing an implementation:
-
-
-We have to take care of the difference between Python string numbering and usual position numbering:
-
-| C in seq -> in string
-|     9 -> 8
-|    78 -> 77
-|   125 -> 124
-|   145 -> 144
-
-| *generate 3 slices from the il2_human*
-| *head <- from the begining and cut between the first cystein and the second*
-| *body <- include  the 2nd and 3rd cystein*
-| *tail <- cut after the 3rd cystein until the end*
-| *replace body cystein by serin*
-| *make new sequence with head body_mutate tail*
-
-
-::
-
-    il2_human = 'MYRMQLLSCIALSLALVTNSAPTSSSTKKTQLQLEHLLLDLQMILNGINNYKNPKLTRMLTFKFYMPKKATELKHLQCLEEELKPLEEVLNLAQSKNFHLRPRDLISNINVIVLELKGSETTFMCEYADETATIVEFLNRWITFCQSIISTLT'
-    head = il2_human[:77]
-    body = il2_human[77:125]
-    tail = il2_human[126:]
-    body_mutate = body.replace('C', 'S')
-    il2_mutate = head + body_mutate + tail
-
 Exercise
 --------
 
@@ -388,7 +355,8 @@ Use the sv40 sequence to test your function.
    >>>
    >>> sequence = fasta_to_one_line(sv40)
    >>> gc_pc = gc_percent(sequence)
-   >>> report = "The sv40 is {0} bp length and has {1:.2%} gc".format(len(sequence), gc_pc)
+   >>> # report = "The sv40 is {0} bp length and has {1:.2%} gc".format(len(sequence), gc_pc)
+   >>> report = f"The sv40 is {len(sequence)} bp length and has {gc_pc:.2%} gc"
    >>> print report
    'The sv40 is 5243 bp length and has 40.80% gc'