import string
# Strength of operations:
# -> [] (brackets)
# 6 -> ~ (negative)
# 5 -> @, $, & (average, maximum, minimum)
# 4 -> %, ! (modulo, factorial)
# 3 -> ^ (power)
# 2 -> *, / (multiplication, division)
# 1 -> +, - (addition, subtraction)
def BinaryOperation(exp, idx):
""" Gets an expression and an index of an operator and returns a tuple with (first_value, operator, second_value). """
first_value = 0
second_value = 0
#Get first value
idx2 = idx -1
if idx2 == 0:
first_value = exp[idx2:idx]
else:
while (idx2 > 0) and (exp[idx2] in string.digits):
idx2 -=1
if (exp[idx2] in ("-")) or (exp[idx2] in string.digits):#-5*3
first_value = exp[idx2:idx]
else:#%5*3
first_value = exp[idx2+1:idx]
#Get second value
idx2 = idx +1
if exp[idx+1] not in string.digits: #If there is something like 1*+5, second_sign will be +.
idx2 += 1 #idx2 will begin from the char after the sign.
while (idx2 < len(exp)) and (exp[idx2] in string.digits):
idx2 += 1
second_value = exp[idx+1:idx2]
return (first_value, exp[idx], second_value)
def UnaryOperation(exp, idx):
""" Gets an expression and an index of an operator and returns a tuple with (operator, value). """
#Get value
idx2 = idx+1
if exp[idx+1] not in string.digits: #If there is something like ~-5, second_sign will be -.
idx2 += 1 #idx2 will begin from the char after the sign.
while (idx2 < len(exp)) and (exp[idx2] in string.digits):
idx2 +=1
return (exp[idx], exp[idx+1:idx2])
def Brackets(exp):
idx = 0
while idx < len(exp):
if exp[idx] == "[":
#Brackets
close_bracket = exp.find("]")
if close_bracket == -1:
raise Exception("Missing closing bracket.")
exp_brackets = exp[idx+1:close_bracket]
value = str(solve(exp_brackets))
exp = exp.replace("[" + exp_brackets + "]", value)
idx = 0 #The len has been changed, scan again.
idx += 1
return Level6(exp)
def Level6(exp):
idx = 0
while idx < len(exp):
if exp[idx] in ("~"):
#Negative
sub_exp = UnaryOperation(exp, idx)
value = ~int(sub_exp[1])
value = str(value)
exp = exp.replace(''.join(sub_exp), value)
idx = 0 #The len has been changed, scan again.
idx += 1
return Level5(exp)
def Level5(exp):
idx = 0
while idx < len(exp):
if exp[idx] in ("@", "$", "&"):
#Average, Maximum and Minimum
sub_exp = BinaryOperation(exp, idx)
first_value = int(sub_exp[0])
second_value = int(sub_exp[2])
if sub_exp[1] == "@":
value = (first_value + second_value)/2
if sub_exp[1] == "$":
value = first_value if first_value > second_value else second_value
if sub_exp[1] == "&":
value = first_value if first_value < second_value else second_value
value = str(value)
exp = exp.replace(''.join(sub_exp), value)
idx = 0 #The len has been changed, scan again.
idx += 1
return Level4(exp)
def Level4(exp):
idx = 0
while idx < len(exp):
if exp[idx] in ("%","!"):
#Modulo and Factorial
if exp[idx] == "%":
sub_exp = BinaryOperation(exp, idx)
value = int(sub_exp[0]) % int(sub_exp[2])
if exp[idx] == "!":
sub_exp = UnaryOperation(exp, idx)
value = reduce(lambda x,y:x*y, range(1, int(sub_exp[1])+1))
value = str(value)
exp = exp.replace(''.join(sub_exp), value)
idx = 0 #The len has been changed, scan again.
idx += 1
return Level3(exp)
def Level3(exp):
idx = 0
while idx < len(exp):
if exp[idx] in ("^"):
#Power
sub_exp = BinaryOperation(exp, idx)
value = int(sub_exp[0]) ** int(sub_exp[2])
value = str(value)
exp = exp.replace(''.join(sub_exp), value)
idx = 0 #The len has been changed, scan again.
idx += 1
return Level2(exp)
def Level2(exp):
idx = 0
while idx < len(exp):
if exp[idx] in ("*", "/"):
#Multiplication and Division
sub_exp = BinaryOperation(exp, idx)
if sub_exp[1] == "*":
value = int(sub_exp[0]) * int(sub_exp[2])
if sub_exp[1] == "/":
value = int(sub_exp[0]) / int(sub_exp[2])
value = str(value)
exp = exp.replace(''.join(sub_exp), value)
idx = 0 #The len has been changed, scan again.
idx += 1
return Level1(exp)
def Level1(exp):
idx = 0
while idx < len(exp):
if (exp[idx] in ("+", "-")) and (idx != 0):
#Addition and Subtraction
sub_exp = BinaryOperation(exp, idx)
if sub_exp[1] == "+":
value = int(sub_exp[0]) + int(sub_exp[2])
if sub_exp[1] == "-":
value = int(sub_exp[0]) - int(sub_exp[2])
value = str(value)
exp = exp.replace(''.join(sub_exp), value)
idx = 0 #The len has been changed, scan again.
idx += 1
return exp
def solve(exp):
exp = Brackets(exp)
return float(exp) if "." in exp else int(exp)
def remove_whitespace(exp):
""" Gets a string and removes all whitespaces and tabs """
exp = exp.replace(" ", "")
exp = exp.replace("\t", "")
return exp
while True:
exp = raw_input("")
exp = remove_whitespace(exp)
print solve(exp)
经过大量的努力，我已经编写了这个程序，我想知道该解决方案的效率以及它是否整洁。
所以我的问题是，这个程序有多简单，有没有更好的方法来重写它？
答案 0 :(得分：1)
只是为了这一点。
>>> eval(raw_input("input calculation: "))
input calculation: 1+1
2
>>> eval(raw_input("input calculation: "))
input calculation: (6*4^2)
26
>>> eval(raw_input("input calculation: "))
input calculation: (3/2.3)*4
5.2173913043478262
对于无辜程序，您可以使用eval
但你真的不应该使用它。它唯一真正的用途是让人感到困惑，如果你自己编写程序并决定要一个计算器，这是一个有趣的新奇事物。
有很多方法可以编写计算器功能。
尝试其他一些答案：
答案 1 :(得分：1)
如果您想在Python中查看一些基于类的自定义评估引擎，这些可能会对您有所帮助：
答案 2 :(得分：0)
again = True
answer = ""
while again is True:
try:
expression = raw_input("Enter your expression: ")
found = False
oper = -1
operator1 = 0
operator2 = 0
while found==False:
if (expression.find("+")>0 and expression.find("+")<len(expression)-1):
found = True
oper = expression.find("+")
operator1 = float(expression[:oper])
operator2 = float(expression[oper+1:])
print "{} + {} = {}".format(operator1,operator2,operator1+operator2)
elif(expression.find("-")>0 and expression.find("-")<len(expression)-1):
found = True
oper = expression.find("-")
operator1 = float(expression[:oper])
operator2 = float(expression[oper+1:])
print "{} - {} = {}".format(operator1,operator2,operator1-operator2)
elif(expression.find("*")>0 and expression.find("*")<len(expression)-1):
found = True
oper = expression.find("*")
operator1 = float(expression[:oper])
operator2 = float(expression[oper+1:])
print "{} * {} = {}".format(operator1,operator2,operator1*operator2)
elif(expression.find("/")>0 and expression.find("/")<len(expression)-1):
found = True
oper = expression.find("/")
operator1 = float(expression[:oper])
operator2 = float(expression[oper+1:])
print "{} / {} = {}".format(operator1,operator2,operator1/operator2)
else:
oper = -1
found = False
print "Incorrect expression, please try again"
break
again = False
answer = raw_input("Try again?: ")
if(answer == "y" or answer=="yes" or answer =="Y" or answer == "YES"):
again = True
else:
again = False
print "Thank you for playing! See you next time."
break
except:
print "Failed, check your expression and try again"