Lists and Text

The last two standard categories. Text is mostly one block you will use constantly and a dozen you probably never will; Lists is how a program holds more than one number under a single name.

Text

print

print ⟨value⟩ writes a line into the black terminal along the bottom of the screen. It is the most useful block in the category by a wide margin, because it is how you find out what a program is actually doing.

Generated by Blocks

drone.takeoff()
print(drone.get_battery())
drone.land()

Put a print between two flight blocks and the terminal tells you the program got that far. Put one inside a loop and it tells you how many passes happened. Nothing in the editor debugs a program faster.

The rest of the category

Block	What it does	What it writes
” ”	A piece of text. Click it and type.	`'hello'`
create text with	Joins pieces together.	`''.join([a, b])`
to x append text ⟨a⟩	Adds to the end of a text variable.	`x = str(x) + str(a)`
length of ⟨a⟩	How many characters.	`len(a)`
is empty ⟨a⟩	True when there are none.	`not len(a)`
in text ⟨a⟩ find first occurrence of ⟨b⟩	Where a piece appears. Counting from 1.	`a.find(b) + 1`
in text ⟨a⟩ get letter # ⟨n⟩	One character. Also first, last, random.	`a[0]`
in text ⟨a⟩ get substring from … to …	A run of characters.	`a[1:3]`
to UPPER CASE ⟨a⟩	Also lower case and Title Case.	`a.upper()`
trim spaces from both sides of ⟨a⟩	Also one side only.	`a.strip()`
count ⟨a⟩ in ⟨b⟩	How many times a piece appears.	`b.count(a)`
replace ⟨a⟩ with ⟨b⟩ in ⟨c⟩	Substitution.	`c.replace(a, b)`
reverse ⟨a⟩	Backwards.	`a[::-1]`

create text with has a gear on it: click it to add more pieces than the two it starts with. Joining a label to a number is the usual reason — “battery: ” and the reading, so the terminal says something you can read rather than a bare number.

Lists

A list is several values under one name, in order.

Block	What it does	What it writes
create list with	A list of values. Gear to add more.	`[a, b, c]`
create list with item ⟨a⟩ repeated n times	The same thing, n times.	`[a] * n`
length of ⟨list⟩	How many items.	`len(x)`
is empty ⟨list⟩	True when there are none.	`not len(x)`
in list ⟨list⟩ find first occurrence of ⟨a⟩	Which position, counting from 1.	`first_index(x, a)`, plus a helper the editor writes
in list ⟨list⟩ get # ⟨n⟩	One item. Also first, last, random, and get-and-remove.	`x[0]`
in list ⟨list⟩ set # ⟨n⟩ to ⟨a⟩	Replaces an item. Also insert and append.	`x[0] = a`
in list ⟨list⟩ get sub-list from … to …	A run of items.	`x[1:3]`
make list from text ⟨a⟩ with delimiter ⟨b⟩	And back the other way.	`a.split(',')`
sort ⟨list⟩	Numeric, alphabetic or ignoring case; ascending or descending.	a sorted copy
reverse ⟨list⟩	Backwards.	`list(reversed(x))`

A flight from a list

The for each item loop in the Loops category takes a list and hands you one item per pass. Put a list of durations in it and each side of a flight has its own length.

Make a variable — route — and set it to a create list with block holding 1, 2, 1 and 2. Then walk it:

A for each item t in list route loop containing fly, wait t seconds, stop, rotate, wait, stop — `t` is the item this pass is on. Dropped into the `wait`, it is how long this side lasts.

Generated by Blocks

route = None
t = None


route = [1, 2, 1, 2]
for t in route:
  drone.fly('forward', 1)
  time.sleep(t)
  drone.fly_stop()
  drone.rotate('right', 1)
  time.sleep(1)
  drone.rotate_stop()

Four sides of 1, 2, 1 and 2 seconds — a short side, a long one, and the same again, described by its shape rather than by four repetitions of the same six blocks. Change the list and the shape changes; nothing else has to move.