How to access a value in a 'Properties' block
To access the value of a certain variable (i.e. YOUNG_MODULUS) included in a Properties block with a certain Id (i.e. 2), do the following:
value = model_part.GetProperties()[YOUNG_MODULUS]
will return all the blocks of Properties in the model part (in Mesh 0 of the model part, to be exact).
specifies the Id of the Properties block you want to visit.
specifies the variable whose variable we want to be returned.