ibdp-classes 0.5.0

An interpreter for pseudocode similar to that used in IBDP Computer Science courses.

IBDP Computer Science Pseudocode Classes

The IB Computer Science documents, Approved notation for developing pseudocode and Pseudocode in Examinations, describe pseudocode and a set of limited-functionality array, collection, stack and queue data structure classes that may come up and be used in exams.

This is a simple Python implementation of an IB pseudocode interpreter and the above restrictive classes, which can be used in programming activities to help familiarize students with the pseudocode and classes.

Under the hood, the classes are simple wrappers over a Python list and the interpreter simply runs some perfunctory tests, translates pseudocode into (really ugly) Python and then does its best to execute the translation and generate helpful error messages.

You can submit issues and requests here.

Install

python -m pip install ibdp-classes

Interpreting IB pseudocode

We can use the library to interpret pseudocode. For example:

example.pseudocode

output "Collection..."
ITEMS = new Collection(1, 2, 3)
ITEMS.resetNext()
loop while ITEMS.hasNext()
    X = ITEMS.getNext()
    output "X =", X
end loop

To interpret:

python -m ibdp_classes example.pseudocode

Output:

Collection...
X = 1
X = 2
X = 3

We can also interpret IB pseudocode from within a Python script by creating and calling a Pseudocode instance. For example:

import ibdp_classes as ib

code = """
output "Array..."
XS = new Array(1, 2, 3, 4, 5)
N = 5
loop I from 0 to N - 1
    output "xs[", I, "] = ", XS[I]
end loop
"""

script = ib.Pseudocode(code)
output = script()
print(output)

Output:

Array...
xs[ 0 ] =  1
xs[ 1 ] =  2
xs[ 2 ] =  3
xs[ 3 ] =  4
xs[ 4 ] =  5

Importing functionality

If we would like to give the pseudocode access to variables or functions defined in Python, we can pass the definitions as a dictionary when calling the Pseudocode instance:

from random import random
from math import floor
import ibdp_classes as ib

code = """
loop I from 1 to 10
    output I, ":", FLOOR(10 * RANDOM())
end loop
"""

script = ib.Pseudocode(code)
output = script({"FLOOR": floor, "RANDOM": random})
print(output)

Example output:

1 : 5
2 : 1
3 : 9
4 : 9
5 : 7
6 : 0
7 : 4
8 : 1
9 : 7
10 : 0

Alternatively, we can have the pseudocode in its own file and the definitions we want available in a separate Python file, and then set -defs to the name of the Python file when we interpret the pseudocode from the command line. For example:

defs.py

from random import random
from math import floor

RANDOM = random
FLOOR = floor

example.pseudo

loop I from 1 to 10
    output I, ":", FLOOR(10 * RANDOM())
end loop

From the command line:

python -m ibdp_classes -defs defs.py example.pseudo

Example output:

1 : 5
2 : 8
3 : 4
4 : 3
5 : 1
6 : 5
7 : 3
8 : 2
9 : 3
10 : 5

Additions to IB pseudocode

function and procedure

In exams, IB pseudocode typically uses output to display results, and either doesn't explicitly define functions or procedures, or else does so informally and inconsistently. I have thus added function and procedure structures to the pseudocode definitions.

For example:

function CONTAINS(NEEDLE, HAYSTACK, N)
    // Where NEEDLE is a string, HAYSTACK is an Array
    // of strings, and N is the length of HAYSTACK.
    FOUND = false
    loop K from 0 to N-1
        if HAYSTACK[K] = NEEDLE then
            FOUND = true
        end if
    end loop
    return FOUND
end function

HAYSTACK = new Array(20, -3, 5, 7, 2, 13, 12, 19)
output "HAYSTACK:", HAYSTACK

output "5 is in HAYSTACK?"
output CONTAINS(5, HAYSTACK, 8)

output "4 is in HAYSTACK?"
output CONTAINS(4, HAYSTACK, 8)

Output:

HAYSTACK: Array { 20, -3, 5, 7, 2, 13, 12, 19 }
5 is in HAYSTACK?
True
4 is in HAYSTACK?
False

Input types using as

In IBDP pseudocode, the keyword input is used to generically collect input from the user, and context is used to determine whether the input should be interpreted as a string, integer or floating point number. I have added as int and as float as appendages to the input statement for when we want to be explicit.

For example:

output "Input an integer."
input COUNT as int

if COUNT mod 2 = 0 then
    output COUNT, "is even..."
else
    output COUNT, "is odd..."
end if

Using the classes within Python scripts

The classed defined by IB can be used directly in Python scripts. While there is not much of a use case for this, it might be helpful as an intermediate step in actually implementing pseudocode.

For example:

from ibdp_classes import Array

def contains(needle: int, haystack: Array[int], n: int) -> bool:
    found = False
    for k in range(n):
        if haystack[k] == needle:
            print("Found!")
            found = True
    return found

haystack = Array(20, -3, 5, 7, 2, 13, 12, 19)
print("haystack:", haystack)

print("5 is in haystack?")
print(contains(5, haystack, 8))

print("4 is in haystack?")
print(contains(4, haystack, 8))