python: rest api with custom query parameters

Question

I want to create an api which is responsible to get the data from the Database.

My Requirment:

GET /products?query=EQUAL(product_id,"56789")

GET /products?query=AND(EQUAL(product_id,"56789"),EQUAL(product_id,"2236"))

GET /products?query=OR(EQUAL(product_id,"56789"),EQUAL(product_id,"369"))

my api query parameters contains operators like EQUAL,OR,AND etc. I dont know how to parse these custom operators.

Can any one suggest a solution to parse these operators?

Answer 1

Frankly, I would use normal SQL query instead of own operators.

But for own operators I would use parser SLY or PLY

Both created by David Beazley . PLY is older, SLY is never and use classes

---

It is hard to describe all code.

Lexer recognizes tokens in string EQUAL , AND , OR , ( , ) , , , variables , strings (values).

Parser checks grammary - it checks if tokens are in correct order. It also converts to SQL query.

from sly import Lexer, Parser

class CalcLexer(Lexer):
    tokens = {EQUAL, AND, OR, VARIABLE, STRING} #, NUMBER}

    EQUAL    = r'EQUAL'  # has to be before VARIABLE
    AND      = r'AND'    # has to be before VARIABLE
    OR       = r'OR'     # has to be before VARIABLE
    VARIABLE = r'[a-zA-Z][a-zA-Z0-9_]*'
    STRING   = r'"[^"]*"'
    #NUMBER  = r'\d+'

    #VARIABLE['EQUAL'] = EQUAL  # if there is no EQUAL before VARIABLE
    #VARIABLE['AND']   = AND    # if there is no AND before VARIABLE
    #VARIABLE['OR']    = OR     # if there is no OR before VARIABLE

    literals = { '(', ')', ',' } 
    ignore = ' \t'

    def error(self, t):
        print(f"Illegal character '{t.STRING[0]}'")
        #self.index += 1

class CalcParser(Parser):
    tokens = CalcLexer.tokens

    #def __init__(self):
        #self.variables = {}

    @_('EQUAL "(" VARIABLE "," STRING ")"')
    def statement(self, p):
        print('[PARSER]', p.VARIABLE, '=', p.STRING)
        #self.variables[p.VARIABLE] = p.STRING
        return f'{p.VARIABLE} = {p.STRING}'

    #@_('EQUAL "(" VARIABLE "," NUMBER ")"')
    #def statement(self, p):
    #    print('[PARSER]', p.VARIABLE, '=', p.NUMBER)
    #    #self.variables[p.VARIABLE] = p.NUMBER
    #    return f'{p.VARIABLE} = {p.NUMBER}'

    #@_('EQUAL "(" VARIABLE "," VARIABLE ")"')
    #def statement(self, p):
    #    print('[PARSER]', p.VARIABLE0, '=', p.VARIABLE1)
    #    #self.variables[p.VARIABLE0] = p.VARIABLE1
    #    return f'{p.VARIABLE0} = {p.VARIABLE1}'

    @_('AND "(" statement "," statement ")"')
    def statement(self, p):
        print('[PARSER]', p.statement0, 'AND', p.statement1)
        return f'({p.statement0}) AND ({p.statement1})'

    @_('OR "(" statement "," statement ")"')
    def statement(self, p):
        print('[PARSER]', p.statement0, 'OR', p.statement1)
        return f'({p.statement0}) OR ({p.statement1})'

#--------------------------------------------------------------------

examples = [
    'EQUAL(product_id,"56789")',
    'AND(EQUAL(product_id,"56789"),EQUAL(product_id,"2236"))',
    'OR(EQUAL(product_id,"56789"),EQUAL(product_id,"369"))',

    # nested
    'OR(EQUAL(product_id,"2236"),AND(EQUAL(product_id,"56789"),EQUAL(product_id,"2236")))',
    'OR(AND(EQUAL(product_id,"56789"),EQUAL(product_id,"2236")),EQUAL(product_id,"2236"))',
    'OR(AND(EQUAL(product_id,"56789"),EQUAL(product_id,"2236")),AND(EQUAL(product_id,"56789"),EQUAL(product_id,"2236")))',

    # with spaces
    'EQUAL  (  product_id ,  "56789" )  ',
    
    #'EQUAL(product_id,"56789")',  # VARIABLE,STRING
    #'EQUAL(product_id,56789)',    # VARIABLE,NUMBER
    #'EQUAL(product_id,other_id)', # VARIABLE,VARIABLE
]

if __name__ == '__main__':
    lexer  = CalcLexer()
    parser = CalcParser()
    for text in examples:
        print('---')
        print('text:', text)
        
        for tok in lexer.tokenize(text):
             print(f'[LEXER] type={tok.type!r}, value={tok.value!r}')
             
        print('result:', parser.parse(lexer.tokenize(text)))