I decided to write my own programming language, of sorts. Essentially, you write code into a text file and the program will run the code inside the text file. The file is provided through a script argument.

# Basic programming language
from operator import eq, ne, lt, gt, le, ge
from random import random
from sys import exit, argv


# Specify file to be run
code = argv([1])


"""
>> - Specify to the user that something will be outputted.
<< - Specify to the user that something will be inputted.
"""


# Dict storing operators
OPERATORS = {
    "==": eq,
    "!=": ne,
    "<=": le,
    ">=": ge,
    "<": lt,
    ">": gt
}


# Dict storing program data
data = {
    "vars": [0] * 100000,
    "rand": random()
}


# Interpret the code
def interpreter(separator):
    for line in open(code, "r").readlines():

        # Split each line
        s_command = line.split(separator)

        # Basic input and output
        if s_command[0] == "$out" and s_command[1] == ">>":
            if s_command[2] in data:
                print data[s_command[2]]
            if s_command[2] not in data:
                print s_command[2]
        if s_command[0] == "$inp" and s_command[1] == "<<":
            inp = raw_input(s_command[2])

        # Assign integer variables
        if s_command[0] == "$assignint" and s_command[1] == "<<":
            data["vars"][int(s_command[2])] = int(s_command[3])

        # Assign string variables
        if s_command[0] == "$assignstr" and s_command[1] == "<<":
            data["vars"][int(s_command[2])] = s_command[3]

        # Return variable values
        if s_command[0] == "$return" and s_command[1] == ">>":
            print data["vars"][int(s_command[2])]

        # Test integer values
        if s_command[0] == "$testint" and s_command[1] == ">>":
            if s_command[3] in OPERATORS:
                print OPERATORS[s_command[3]](
                    int(s_command[2]),
                    int(s_command[4]))

        # Test string values
        if s_command[0] == "$teststr" and s_command[1] == ">>":
            if s_command[3] in OPERATORS:
                print OPERATORS[s_command[3]](
                    s_command[2],
                    s_command[4])

        # Test variable values
        if s_command[0] == "$testvar" and s_command[1] == ">>":
            if s_command[3] in OPERATORS:
                print OPERATORS[s_command[3]](
                    data["vars"][int(s_command[2])],
                    data["vars"][int(s_command[4])])

        # Terminate the program
        if s_command[0] == "$exit" and s_command[1] == ">>":
            exit(int(s_command[2]))


# Run the interpreter
if __name__ == "__main__":
    while True:
        interpreter(":")

Here's an example of a code file:

$out:>>:Hello world.
$inp:<<:[input]>

$assignint:<<:0:10
$assignint:<<:1:11

$return:>>:0
$return:>>:1

$testvar:>>:0:==:1
$testvar:>>:0:!=:1

$exit:>>:0

All I'm really looking for is a way to turn that ugly if/else chain into something prettier without changing the original syntax.

up vote 6 down vote accepted

It looks like all your tests follow the pattern

if s_command[0] == "$xxxxx" and s_command[1] == "yyyyy":

So what you can do is create a tuple of the first two elements of s_command:

instr = tuple(s_command[:2])

Then, you can do

if instr == ("$xxxxx", "yyyyy"):

Next, you can use a dictionary to collect all your instructions in one place:

Instructions = {
    ("$out", ">>"): do_out,
    ("$inp", "<<"): do_inp,
    ("$assignint", "<<"): do_assignint,
    ...
}

Then you would define a number of functions, one for each instruction, such as

def do_inp(s_command):
    inp = raw_input(s_command[2])

and call your methods with

Instructions[instr](s_command)

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