An interpreter for pseudocode similar to that used in IBDP Computer Science courses.
Project description
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
At the command line:
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
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
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
Extensions
In addition to being able to add bespoke functionality using -defs
, a few wrappers are available as extensions that are not defined by IB but that can be helpful in certain lesson scenarios. We can access these extensions using -ext
and passing a string of extensions we would like to expose the pseudocode to.
Extensions available:
strings
The strings
extension exposes the following functions, which can helpful in activities involving string searches and manipulation.
-
SUBSTRING(STRING, START, END)
The substring of
STRING
starting at indexSTART
(inclusive) and ending at indexEND
(exclusive). -
CHARACTER(STRING, INDEX)
The character in
STRING
at indexINDEX
. -
UPPERCASE(STRING)
andLOWERCASE(STRING)
The uppercase and lowercase respectively of
STRING
. -
REPLACE(STRING, OLD, NEW)
A copy of
STRING
withOLD
replaced withNEW
. -
CONTAINS(STRING, SUBSTRING)
Whether
SUBSTRING
occurs inSTRING
. -
STRING_LENGTH(STRING)
The length of
STRING
. -
REPEAT(STRING, N)
A string consisting of
STRING
repeatedN
times.
math
The math
extension exposes the following constants and functions, which can be helpful in activities involving math problems.
-
PI
An approximation of π.
-
TO_DEGREES(X)
Converts
X
radians to degrees. -
TO_RADIANS(X)
Converts
X
degrees to radians. -
SIN(X)
,COS(X)
&TAN(X)
The sine, cosine and tangent respectively of
X
. -
ARCSIN(X)
,ARCCOS(X)
&ARCTAN(X)
The arcsine, arccosine and arctangent respectively of
X
. -
E
An approximation of e.
-
LOG(X)
The base 10 logarithm of
X
. -
LN(X)
The base e logarithm of
X
. -
LOG(X, B)
The base
B
logarithm ofX
. -
EXP(X)
The exponential of
X
. -
POWER(X, P)
X
raised to the power ofP
. -
SQUARE(X)
The square of
X
. -
SQUARE_ROOT(X)
The square root of
X
.
Example:
examples/extensions/sine.pseudo
A = 30
N = 20
loop I from 0 to N - 1
SPACES = (A * (SIN(I * 2 * PI / N) + 1))
output REPEAT(" ", SPACES), "*"
end loop
From the command line:
python -m ibdp_classes -ext 'strings math' examples/extensions/sine.pseudo
Output:
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
bits
The bits
extension exposes the following functions, which can be helpful in activities involving bit manipulation.
-
SET_BIT(X, P)
Integer
X
with bit at positionP
set. -
UNSET_BIT(X, P)
Integer
X
with bit at positionP
unset. -
BIT_IS_SET(X, P)
Whether the bit at position
P
of integerX
is set. -
BIT_AND(A, B)
,BIT_OR(A, B)
,BIT_XOR(A, B)
Bitwise conjunction, disjunction and exclusive disjunction respectively of integers
A
andB
. -
BIT_NOT_8(X)
,BIT_NOT_16(X)
andBIT_NOT_32(X)
Bitwise negation of integer
X
assuming 8, 16 or 32 bits respectively in the structure
Example:
examples/extensions/binary.pseudo
TEMPLATE = "[7][6][5][4][3][2][1][0]"
output "Input an integer from 0 to 255."
input VALUE as int
loop I from 0 to 7
BIT_TEMPLATE = REPLACE("[I]", "I", I)
if BIT_IS_SET(VALUE, I) then
TEMPLATE = REPLACE(TEMPLATE, BIT_TEMPLATE, 1)
else
TEMPLATE = REPLACE(TEMPLATE, BIT_TEMPLATE, 0)
end if
end loop
output "In binary,", VALUE, "is:", TEMPLATE
In the command line:
python -m ibdp_classes -ext 'strings bits' examples/extensions/binary.pseudo
Example output:
Input an integer from 0 to 255.
42
In binary, 42 is: 00101010
turtle
The turtle
extension exposes some of the functionality of the Python turtle module, which can be helpful in fun, beginner-friendly (and more advanced) programming activities. See src/extensions/turtle_defs.py
for details.
Example:
examples/extensions/fractal.pseudo
procedure FRACTAL(LENGTH, DEPTH)
DISTANCE = LENGTH / 3
if DEPTH = 0 then
GO_FORWARD(DISTANCE)
TURN_LEFT(60)
GO_FORWARD(DISTANCE)
TURN_RIGHT(120)
GO_FORWARD(DISTANCE)
TURN_LEFT(60)
GO_FORWARD(DISTANCE)
else
FRACTAL(DISTANCE, DEPTH - 1)
TURN_LEFT(60)
FRACTAL(DISTANCE, DEPTH - 1)
TURN_RIGHT(120)
FRACTAL(DISTANCE, DEPTH - 1)
TURN_LEFT(60)
FRACTAL(DISTANCE, DEPTH - 1)
end if
end procedure
WIDTH = 600
Y = -250
loop DEPTH from 1 to 3
PEN_UP()
SET_X(-WIDTH / 2)
SET_Y(Y)
PEN_DOWN()
FRACTAL(WIDTH, DEPTH)
Y = Y + 200
end loop
HIDE_TURTLE()
WAIT()
At the command line:
python -m ibdp_classes -ext turtle examples/extensions/fractal.pseudo
Output:
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))
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