有没有一种方法可以自动生成有效的算术表达式? [英] Is there a way to autogenerate valid arithmetic expressions?
问题描述
我目前正在尝试创建一个Python脚本，该脚本将自动生成有效的以空格分隔的算术表达式.但是，我得到的示例输出如下所示:( 32 - 42 / 95 + 24 ( ) ( 53 ) + ) 21
尽管我对空括号完全可以接受，但我无法在计算中使用此自动生成的表达式，因为在24和53之间没有运算符，而末尾21之前的+没有第二个参数.
我想知道的是，有没有一种方法可以使用Pythonic解决方案解决/修复这些错误? (并且在任何人指出之前，我将是第一个承认我在下面发布的代码可能是我推送并遵循的最糟糕的代码……很好，Python的核心宗旨很少.)
import random
parentheses = ['(',')']
ops = ['+','-','*','/'] + parentheses
lines = 0
while lines < 1000:
fname = open('test.txt','a')
expr = []
numExpr = lines
if (numExpr % 2 == 0):
numExpr += 1
isDiv = False # Boolean var, makes sure there's no Div by 0
# isNumber, isParentheses, isOp determine whether next element is a number, parentheses, or operator, respectively
isNumber = random.randint(0,1) == 0 # determines whether to start sequence with number or parentheses
isParentheses = not isNumber
isOp = False
# Counts parentheses to ensure parentheses are matching
numParentheses = 0
while (numExpr > 0 or numParentheses > 0):
if (numExpr < 0 and numParentheses > 0):
isDiv = False
expr.append(')')
numParentheses -= 1
elif (isOp and numParentheses > 0):
rand = random.randint(0,5)
expr.append(ops[rand])
isDiv = (rand == 3) # True if div op was just appended
# Checks to see if ')' was appended
if (rand == 5):
isNumber = False
isOp = True
numParentheses -= 1
# Checks to see if '(' was appended
elif (rand == 4):
isNumber = True
isOp = False
numParentheses += 1
# All other operations go here
else:
isNumber = True
isOp = False
# Didn't add parentheses possibility here in case expression in parentheses somehow reaches 0
elif (isNumber and isDiv):
expr.append(str(random.randint(1,100)))
isDiv = False
isNumber = False
isOp = True
# If a number's up, decides whether to append parentheses or a number
elif (isNumber):
rand = random.randint(0,1)
if (rand == 0):
expr.append(str(random.randint(0,100)))
isNumber = False
isOp = True
elif (rand == 1):
if (numParentheses == 0):
expr.append('(')
numParentheses += 1
else:
rand = random.randint(0,1)
expr.append(parentheses[rand])
if rand == 0:
numParentheses += 1
else:
numParentheses -= 1
isDiv = False
numExpr -= 1
fname.write(' '.join(expr) + '\n')
fname.close()
lines += 1
是的，您可以以Python方式生成随机算术表达式.但是，您需要更改方法.不要试图生成一个字符串并计算paren.而是生成一个随机的表达式树，然后将其输出.
通过表达式树，我的意思是一个名为Expression的类的实例，其子类为Number，PlusExpression, MinusExpression , 'TimesExpression，DivideExpression和ParenthesizedExpression.除Number以外，每个其他项都具有类型为Expression的字段.给每个适当的__str__方法.生成一些随机表达式对象，然后仅打印根".
您可以从这里拿走它吗，还是要我把它编码起来?
附录:一些示例入门代码.不会生成随机表达式(还可以吗?)，但是可以添加....
# This is just the very beginning of a script that can be used to process
# arithmetic expressions. At the moment it just defines a few classes
# and prints a couple example expressions.
# Possible additions include methods to evaluate expressions and generate
# some random expressions.
class Expression:
pass
class Number(Expression):
def __init__(self, num):
self.num = num
def __str__(self):
return str(self.num)
class BinaryExpression(Expression):
def __init__(self, left, op, right):
self.left = left
self.op = op
self.right = right
def __str__(self):
return str(self.left) + " " + self.op + " " + str(self.right)
class ParenthesizedExpression(Expression):
def __init__(self, exp):
self.exp = exp
def __str__(self):
return "(" + str(self.exp) + ")"
e1 = Number(5)
print e1
e2 = BinaryExpression(Number(8), "+", ParenthesizedExpression(BinaryExpression(Number(7), "*", e1)))
print e2
**附录2 **
重新使用Python真的很有趣.我无法抗拒实现随机表达式生成器.它基于上面的代码.不好意思！
from random import random, randint, choice
def randomExpression(prob):
p = random()
if p > prob:
return Number(randint(1, 100))
elif randint(0, 1) == 0:
return ParenthesizedExpression(randomExpression(prob / 1.2))
else:
left = randomExpression(prob / 1.2)
op = choice(["+", "-", "*", "/"])
right = randomExpression(prob / 1.2)
return BinaryExpression(left, op, right)
for i in range(10):
print(randomExpression(1))
这是我得到的输出:
(23)
86 + 84 + 87 / (96 - 46) / 59
((((49)))) + ((46))
76 + 18 + 4 - (98) - 7 / 15
(((73)))
(55) - (54) * 55 + 92 - 13 - ((36))
(78) - (7 / 56 * 33)
(81) - 18 * (((8)) * 59 - 14)
(((89)))
(59)
太漂亮了.我认为它淘汰了太多父母.也许更改在括号表达式和二进制表达式之间进行选择的可能性可能会很好....
I'm currently trying to create a Python script that will autogenerate space-delimited arithmetic expressions which are valid. However, I get sample output that looks like this: ( 32 - 42 / 95 + 24 ( ) ( 53 ) + ) 21
While the empty parentheses are perfectly OK by me, I can't use this autogenerated expression in calculations since there's no operator between the 24 and the 53, and the + before the 21 at the end has no second argument.
What I want to know is, is there a way to account for/fix these errors using a Pythonic solution? (And before anyone points it out, I'll be the first to acknowledge that the code I posted below is probably the worst code I've pushed and conforms to...well, very few of Python's core tenets.)
import random
parentheses = ['(',')']
ops = ['+','-','*','/'] + parentheses
lines = 0
while lines < 1000:
fname = open('test.txt','a')
expr = []
numExpr = lines
if (numExpr % 2 == 0):
numExpr += 1
isDiv = False # Boolean var, makes sure there's no Div by 0
# isNumber, isParentheses, isOp determine whether next element is a number, parentheses, or operator, respectively
isNumber = random.randint(0,1) == 0 # determines whether to start sequence with number or parentheses
isParentheses = not isNumber
isOp = False
# Counts parentheses to ensure parentheses are matching
numParentheses = 0
while (numExpr > 0 or numParentheses > 0):
if (numExpr < 0 and numParentheses > 0):
isDiv = False
expr.append(')')
numParentheses -= 1
elif (isOp and numParentheses > 0):
rand = random.randint(0,5)
expr.append(ops[rand])
isDiv = (rand == 3) # True if div op was just appended
# Checks to see if ')' was appended
if (rand == 5):
isNumber = False
isOp = True
numParentheses -= 1
# Checks to see if '(' was appended
elif (rand == 4):
isNumber = True
isOp = False
numParentheses += 1
# All other operations go here
else:
isNumber = True
isOp = False
# Didn't add parentheses possibility here in case expression in parentheses somehow reaches 0
elif (isNumber and isDiv):
expr.append(str(random.randint(1,100)))
isDiv = False
isNumber = False
isOp = True
# If a number's up, decides whether to append parentheses or a number
elif (isNumber):
rand = random.randint(0,1)
if (rand == 0):
expr.append(str(random.randint(0,100)))
isNumber = False
isOp = True
elif (rand == 1):
if (numParentheses == 0):
expr.append('(')
numParentheses += 1
else:
rand = random.randint(0,1)
expr.append(parentheses[rand])
if rand == 0:
numParentheses += 1
else:
numParentheses -= 1
isDiv = False
numExpr -= 1
fname.write(' '.join(expr) + '\n')
fname.close()
lines += 1
Yes, you can generate random arithmetic expressions in a Pythonic way. You need to change your approach, though. Don't try to generate a string and count parens. Instead generate a random expression tree, then output that.
By an expression tree, I mean an instance of a class called, say, Expression with subclasses Number, PlusExpression,MinusExpression, 'TimesExpression, DivideExpression, and ParenthesizedExpression. Each of these, except Number will have fields of type Expression. Give each a suitable __str__ method. Generate some random expression objects and just print the "root."
Can you take it from here or would you like me to code it up?
ADDENDUM: Some sample starter code. Doesn't generate random expressions (yet?) but this can be added....
# This is just the very beginning of a script that can be used to process
# arithmetic expressions. At the moment it just defines a few classes
# and prints a couple example expressions.
# Possible additions include methods to evaluate expressions and generate
# some random expressions.
class Expression:
pass
class Number(Expression):
def __init__(self, num):
self.num = num
def __str__(self):
return str(self.num)
class BinaryExpression(Expression):
def __init__(self, left, op, right):
self.left = left
self.op = op
self.right = right
def __str__(self):
return str(self.left) + " " + self.op + " " + str(self.right)
class ParenthesizedExpression(Expression):
def __init__(self, exp):
self.exp = exp
def __str__(self):
return "(" + str(self.exp) + ")"
e1 = Number(5)
print e1
e2 = BinaryExpression(Number(8), "+", ParenthesizedExpression(BinaryExpression(Number(7), "*", e1)))
print e2
** ADDENDUM 2 **
Getting back into Python is really fun. I couldn't resist implementing the random expression generator. It is built on the code above. SORRY ABOUT THE HARDCODING!!
from random import random, randint, choice
def randomExpression(prob):
p = random()
if p > prob:
return Number(randint(1, 100))
elif randint(0, 1) == 0:
return ParenthesizedExpression(randomExpression(prob / 1.2))
else:
left = randomExpression(prob / 1.2)
op = choice(["+", "-", "*", "/"])
right = randomExpression(prob / 1.2)
return BinaryExpression(left, op, right)
for i in range(10):
print(randomExpression(1))
Here is the output I got:
(23)
86 + 84 + 87 / (96 - 46) / 59
((((49)))) + ((46))
76 + 18 + 4 - (98) - 7 / 15
(((73)))
(55) - (54) * 55 + 92 - 13 - ((36))
(78) - (7 / 56 * 33)
(81) - 18 * (((8)) * 59 - 14)
(((89)))
(59)
Ain't tooooo pretty. I think it puts out too many parents. Maybe change the probability of choosing between parenthesized expressions and binary expressions might work well....
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