Programming Languages Transcript – Lecture of 13th October at 13:15

(* Is the value 2 intentionally equal to 2? *)
>>> 2 is 2

(* Does this also work for strings? *)
>>> “Hello” == “Hello”
>>> “Hello” is “Hello”

(* Does it also work for empty lists? *)
>>> [] == []
>>> [] is []

(* A different method of variable instantiation, does b point to an empty list and then a to the same empty list? *)
>>> a = b = []
>>> a is b

(* Usage of the reverse method on lists *)
>>> a = [1,2,3]
>>> type(a)
>>> a.reverse
>>> a.reverse()
>>> a
>>> a.reverse()
>>> a
>>> reversed(a)
>>> b = reversed(a)
>>> b

(* Creating an iterator over the list a, going backwards *)
>>> b = reversed(a)

(* The iterator is consumable, it only returns this result once *)
>>> list(b)
>>> list(b)

(* Normally, lists aren’t consumable *)
>>> b = [1,2,3]
>>> list(b)
>>> list(b)

(* Showing the type difference between lists and iterators *)
>>> b = [1,2,3]
>>> type(b)
>>> b = reversed([1,2,3])
>>> type(b)

(* Returning an item from a list iterator one by one *)
>>> b = reversed([1,2,3])
>>> next(b)
>>> next(b)
>>> next(b)

(* Iterating over a list normally *)
>>> b = iter([1,2,3])
>>> next(b)

(* You can change the list that an iterator is pointing to *)
>>> a = [1,2,3]
>>> b = reversed(a)

(* Does using append work? *)
>>> a.append(42)
>>> list(b)

(* Does using a direct assignment on the index work? *)
>>> a[0] = 42
>>> list(b)

(* Lists can hold multiple types at once, including a list within a list. What is the length of this list? *)
>>> a = [99, "bottles of beer", ["on","the","wall"]]
>>> len(a)

(* Using the join method, we can add more characters to the end of a string. What will this return? *)
>>> " "
>>> " ".join([a[1]]+a[2])
>>> "@".join([a[1]]+a[2])

(* Casting to the string type. What will these method calls return? *)
>>> str(9)
>>> str(0b11111111)
>>> str(“2”)
>>> str([“2”,”3”])

(* Casting to the integer type. What will these method calls return? *)
>>> int(“400”)
>>> int(None)
>>> int([“3”])
>>> int(4.0)
>>> int(4.7)
>>> int(-4.7)

(* Example of instantiating a range, and its type *)
>>> range(10)
>>> type(range(10))

(* You can create a range of any size, it does not actually calculate the value until it’s called. May crash your system. *)
>>> type(range(2**100000000))
>>> list(range(2**100000000))

(* Instantiating a list to a range 0-9 *)
>>> list(range(10))
[0,1,2,3,4,5,6,7,8,9]