pseudocode

This is a script to convert pseudocode (as taught at Birkbeck College London) into a python script, which you can then run to see your pseudocode in action.

(You need to have Python installed on your computer -- do an internet search on how to install this, if you need to. Or copy-and-paste the python files into an online Python interpreter like this one: https://replit.com/ )

There are example pseudocode scripts (ex1.txt - ex15.txt) in the examples folder, and the resulting python scripts (ex1.py - ex15.py) in the converted folder.

The converter will not work for all examples, but it should work for "simple" pseudocode. There is a limited set of pseudocode commands it can recognise. These are described below in the section "Supported Pseudocode". If you don't type these as specified, it may fail.

If there are errors in the pseudocode, the conversion can catch some of them (e.g. an IF without an ENDIF) but it will not catch others (e.g. an ELSEIF after an ELSE, within the same IF statement), otherwise the script would have to do more complicated checks... and I have other things to do :-)

Most likely, if there is a problem in the pseudocode, the conversion will fail with some Python errors. The displayed error might give you a clue about the problem, but you might have to look back at the pseudocode to find it. If the following notes (or the script itself) don't help you to understand the issue, try to contact me.

How to use

You can download the files from this repo as a ZIP file. (If you are viewing this in GitHub, click on the "Code" button above-right, and then click "Download as ZIP".) You should be able to open the ZIP file on your computer and/or extract it to a convenient location. (Or if you have git installed on your computer, from the command prompt / shell, run: git clone https://github.com/firosuke/pseudocode/)

If all else fails, just click on pseudo.py file and copy-paste the code, save it onto your computer. The only essential file is the Python script, pseudo.py. (There are some example pseudocode files and example data in the examples folder.)

Convenient way

I find the most convenient way to use it is this. From your terminal (Linux/Mac) or command prompt (Windows), navigate to the folder where you have placed pseudo.py, and run:

python pseudo.py (pseudocode file name)

for example:

python pseudo.py examples/ex12.txt

By defaul It will display some information about what it is doing while it runs. If successful, it will put the generated python code in a file. By default, it goes into output.py in the current folder. You can then run the generated python script. For example:

python output.py

If the conversion went well, you will see your pseudocode in action.

Note that if there are something wrong, Python will get confused and you will see Python errors. As mentioned above, this may happen if you don't type the pseudocode in a particular way that this script recognises: see "Supported Pseudocode" below. If you think you've done it correctly, there may be a problem or unmentioned limitation of this script -- let me know.

Custom output location

If you want to specify the output file yourself, you can run the script like this:

python pseudo.py (path to your source file) (destination file)

For example: python pseudo.py examples/ex12.txt simple-interest.py

If you leave out the destination file, it will write the generated python code into "output.py" as described above.

In the above example, you would then run:

python simple-interest.py

(Lastly, if you don't specify the source pseudocode, it defaults to "input.txt" in the current folder.)

Supported Pseudocode

DECLARE (CONSTANT/CONST) (type) (variable) (can be followed by: , (variable), (variable), ...)
DISPLAY "this string" + some expression + "that string", etc. (See below)
IF condition, ELSE IF, ELSE, ENDIF
WHILE condition, ENDWHILE
SET variable = expression
GET variable
OPEN "your-file-path" (see note below)
READ variable
WRITE variable
CLOSE "your-file-path"
Boolean operators AND, OR, NOT; and values True or False
ROUND(number, decimalPlaces)
CONCAT(string1, string2, ...)
RANDOM(upper, lower)
CHARAT(string, index)
SUBSTRING(string, start, end) (including the end index)
Type conversions: (String), (Integer), (Double), (Boolean), followed by an expression which must be in brackets. E.g.: (Integer)(stockPrice)

Notes (please read!):

General syntax

Keywords like GET and READ are expected to be in capitals as shown above.

Variable names are allowed to contain upper- and lower-case letters, and numbers, and underscore. Nothing else -- in particular, no spaces. Strings are expected to appear in double quotes "" (or the fancier quotes “”). You might get away with single quotes.

Types

The datatypes mentioned in the course are: Boolean, String, Double (i.e. "float" or decimal), Integer, Character. (Aside: These are translated into python as: bool, str, float, int, str.)

Types like Boolean, String, Character, and Boolean values True, False, are expected to have this capitalisation (first letter upper-case, others lower-case).

For simplicity, line numbers, end-of-line semicolons, spacing, and CONSTANT declarations are ignored or removed. That doesn't mean you should leave them out of your pseudocode :-)

Arrays

Variables can be arrays. You can declare them as in this example:

DECLARE Double totalWeight, weights[], averageWeight

Here, totalWeight and averageWeight are Doubles, and weights is an array of Doubles. You can access the value at position i in the array like this: weights[i].

You can put values into an array simply by assigning them directly: e.g. SET names[25] = "Adam". (Aside: Most programming languages don't let you do this. You have to initialise the array. But we can get around this detail by secretly using Python dictionaries to represent arrays, because if a dictionary doesn't yet have a key (e.g. 25 above), when we do the assignment, it will simply create the new key.)

Input and Output

If you GET user input into a variable, or READ a file into a variable, that variable should have a declared type. The generated script will try to get one line of input from a file (READ) or the user (GET), and convert it to that type. If no type is declared, the script will display a warning that we are assuming it is a string (which may not be what you want).

You can GET or READ into one cell of an array. For example: "GET scores[0]". Or, "READ name[i]".

After you OPEN a file, you can either READ or WRITE, but not both. When you no longer need it, you should CLOSE the file. (You can OPEN it again if you need to either READ or WRITE again.) For simplicity, you can only open one file at a time, and each OPEN should be followed by a matching CLOSE, simply the next one in the file. (Aside: In Python you have to decide when you open a file, whether you want to read or write from it. But in pseudocode, we ignore this detail. So the conversion has to do some extra work to allow it.)

DISPLAY commands

DISPLAY commands are essentially reduced to "print" statements in python. In a DISPLAY command, you can join any kind of data together with +:

DISPLAY "Hello " + 4 + " my " + False

Note that Strings are joined (and also concatenated) without spaces, so if you want them, you have to add them yourself:

DISPLAY "a" + "b" + "c!" -----> displays "abc!"

DISPLAY "a " + " b " + " c!" -----> displays "a b c!"

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