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import random
# Write an evaluator for a small language:
# - operators: '+', '*'
# - operands: Integers
#
# E.g. evaluate("2+14*90+5*16")
def tokenize(xs):
result = []
i = 0
while i < len(xs):
current = xs[i]
if current in {'*', '+'}:
result.append(current)
i += 1
continue
elif current == ' ':
i += 1
continue
else:
i += 1
while i < len(xs) and xs[i] in {str(x) for x in range(10)}:
current += xs[i]
i += 1
result.append(int(current))
return result
def ast(tokens):
result = []
series = []
for token in tokens:
if token == '+':
result.append(series)
series = []
elif token == '*':
continue
else:
series.append(token)
if series:
result.append(series)
return result
def product(xs):
result = 1
for x in xs:
result *= x
return result
def evaluate(x):
tokens = tokenize(x)
tree = ast(tokens)
return sum([product(xs) for xs in tree])
n = 7
operands = [random.randint(0, 100) for _ in range(n)]
operators = [random.choice(['+','*']) for _ in range(n - 1)]
expr = []
for i in range(n - 1):
expr.append(operands[i])
expr.append(operators[i])
expr.append(operands[-1])
expr = ' '.join([str(x) for x in expr])
print("Expression: {}".format(expr))
print("Tokens: {}".format(tokenize(expr)))
print("AST: {}".format(ast(tokenize(expr))))
print("Answer: {}".format(evaluate(expr)))
assert evaluate(expr) == eval(expr)
print("Success!")
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