Compute "% off" calculations

take_n_percent_off_there

import sys

import ply.lex as lex
import ply.yacc as yacc

tokens = ['NUMBER', 'MINUS', 'PERCENT']
t_ignore = ' \t'
t_MINUS = r'-'
t_PERCENT = r'%'

def t_NUMBER(t):
    r'\d+(\.\d*)?'
    t.value = float(t.value)
    return t

def t_error(t):
    print(f'Illegal character {t.value[0]!r}')
    t.lexer.skip(1)

lex.lex()

def p_expr(p):
    'expr : NUMBER MINUS NUMBER PERCENT'
    p[0] = p[1] - (p[1] * p[3] / 100)

def p_error(p):
    print(f'Syntax error at {p.value!r}')

yacc.yacc()

if len(sys.argv) < 2:
    print('expr required')
    sys.exit(1)

expr = ' '.join(sys.argv[1:])
result = yacc.parse(expr)
print(f'{result:.2f}')