class Calculator:

def $\_\_$init$\_\_($self$)$:

self.$\_\_$expr $=$ None

@property

def getExpr$($self$)$:

return self.$\_\_$expr

def setExpr$($self$,$ new$\_$expr$)$:

if isinstance$($new$\_$expr, str$)$:

self.$\_\_$expr$=$new$\_$expr

else:

print$(\text{'}$setExpr error: Invalid expression'$)$

return None

def $\_$isNumber$($self$,$ txt$)$:

# YOUR CODE STARTS HERE

try:

float$($txt$)$

return True

except ValueError:

return False

pass

def $\_$getPostfix$($self$,$ txt$)$:

# YOUR CODE STARTS HERE

postfixStack $=$ Stack$()$ # method must use postfixStack to compute the postfix expression

precedence $=\{\text{'}+\text{'}$: $1,\text{'}-\text{'}$: $1,\text{'}*\text{'}$: $2,\text{'}/\text{'}$: $2,\text{'}^\text{'}$: $3\}$

output $=\text{'}\text{'}$

for char in txt$.$split$()$:

if self.$\_$isNumber$($char$)$:

output $+=$ char $+\text{'}\text{'}$

elif char in precedence.keys$()$:

while not postfixStack.isEmpty$()$ and precedence.get$($postfixStack$.$peek$(),0)>=$ precedence.get$($char$,0)$:

output $+=$ postfixStack.pop$()+\text{'}\text{'}$

postfixStack.push$($char$)$

elif char $==\text{'}(\text{'}$:

postfixStack.push$($char$)$

elif char $==\text{'})\text{'}$:

while not postfixStack.isEmpty$()$ and postfixStack.peek$()!=\text{'}(\text{'}$:

output $+=$ postfixStack.pop$()+\text{'}\text{'}$

postfixStack.pop$()$ # Discard $\text{'}(\text{'}$

else:

print$("$Invalid character in expression:", char$)$

return None

while not postfixStack.isEmpty$()$:

output $+=$ postfixStack.pop$()+\text{'}\text{'}$

return output.strip$()$

@property

def calculate$($self$)$:

if not isinstance$($self$.\_\_$expr,str$)$ or len$($self$.\_\_$expr$)<=0$:

print$("$Argument error in calculate"$)$

return None

calcStack $=$ Stack$()$ # method must use calcStack to compute the expression

# YOUR CODE STARTS HERE

postfix$\_$expr $=$ self.$\_$getPostfix$($self$.\_\_$expr$)$

if postfix$\_$expr is None:

print$("$Invalid expression"$)$

return None

for token in postfix$\_$expr.split$()$:

if self.$\_$isNumber$($token$)$:

calcStack.push$($float$($token$))$

else:

if calcStack.isEmpty$()$ or calcStack.size$()<2$: # Check for missing operands

print$("$Invalid expression: missing operands"$)$

return None

operand$2=$ calcStack.pop$()$

operand$1=$ calcStack.pop$()$

if token $==\text{'}+\text{'}$:

calcStack.push$($operand$1+$ operand$2)$

elif token $==\text{'}-\text{'}$:

calcStack.push$($operand$1-$ operand$2)$

elif token $==\text{'}*\text{'}$:

calcStack.push$($operand$1*$ operand$2)$

elif token $==\text{'}/\text{'}$:

if operand$2==0$:

print$("$Division by zero error"$)$

return None

calcStack.push$($operand$1/$ operand$2)$

elif token $==\text{'}^\text{'}$:

calcStack.push$($operand$1**$ operand$2)$

else:

print$("$Invalid operator:", token$)$

return None

if calcStack.isEmpty$()$ or calcStack.size$()!=1$: # Check for missing operators

print$("$Invalid expression: missing operators"$)$

return None

return calcStack.pop$()$

pass

$4\mathrm{.}0)$ Testing postfix doctest cases $(0/0)$ Testing code....

$>>>$ x$=$Calculator$()$

$>>>$ x$.\_$getPostfix$(\text{'}2^4\text{'})\text{'}2\mathrm{.}04\mathrm{.}0^\text{'}$

$>>>$ x$.\_$getPostfix$(\text{'}2\mathrm{.}1*5+3^2+1+4\mathrm{.}45\text{'})\text{'}2\mathrm{.}15\mathrm{.}0*3\mathrm{.}02\mathrm{.}0^+1\mathrm{.}0+4\mathrm{.}45+\text{'}$

$>>>$ x$.\_$getPostfix $(\text{'}2\mathrm{.}1*5+3^2+1+4\mathrm{.}45\text{'},\text{'}2\mathrm{.}6786(\{5+3\}^2+[1+4])\text{'})\text{'}2\mathrm{.}67865\mathrm{.}03\mathrm{.}0+2\mathrm{.}0^1\mathrm{.}04\mathrm{.}0++*\text{'}$

Expected output: $2\mathrm{.}04\mathrm{.}0^$

Your code returned: $24^$

$>>>$ Incorrect answer Expected output: $2\mathrm{.}15\mathrm{.}0*3\mathrm{.}02\mathrm{.}0^+1\mathrm{.}0+4\mathrm{.}45+$

Your code returned: $2\mathrm{.}15*32^+1+4\mathrm{.}45+$

$>>>$ Incorrect answer Expected output: $2\mathrm{.}67865\mathrm{.}03\mathrm{.}0+2\mathrm{.}0^1\mathrm{.}04\mathrm{.}0++*$ Invalid character in expression: $\{$ Your code returned: None NOTE: Method is not returning a string Test Failed: True $!=$ False

$5\mathrm{.}0)$ Testing calculate doctest cases $(0/0)$ Testing code....

$>>>$ x$=$Calculator$()>>>$ x$.$setExpr$(\text{'}2-3*4\text{'})$

$>>>$ x$.$calculate $-10\mathrm{.}0$

$>>>$ x$.$setExpr$(\text{'}2\mathrm{.}5+3*[2+(3\mathrm{.}0)(5^2-2*3^(2))*(4)]*(2/8+2\{3-1/3\})-2/3^2\text{'})$

$>>>$ x$.$calculate $1442\mathrm{.}7777777777778$ Expected output: $-10\mathrm{.}0$ Test Failed: 'Stack' object has no attribute 'size'

Debug the code pls