[Python] Turning infix notation to prefix notation has problems in formatting (Python)

I'm trying to create a program that turns infix notation to prefix notation, regardless of what kind of number the user inputs(it could be a variable like A B or an integer like 3 34 23):

def isDigit(To_check: str):
ignore = ['-', '+', '*', '/', '^', '(', ')', '%']
if not To_check in ignore: return True
else: return False
def to_prefix(infix_expression: str):
temp = list(infix_expression)
output = []
operator = []
elements = []
priority = {'(':0, ')':0, '+':1, '-':1, '/':2, '*':2, '^':3}
temp2 = ""
for i in range(len(temp)):
reachedOp = False
for op, val in priority.items():
if temp != op: continue
else:
reachedOp = True
break
if not reachedOp: temp2 += temp
else:
if temp2 == '': continue
elements.append(temp2)
temp2 = ""
if temp2 != '':
elements.append(temp2)
del temp, temp2
for c in infix_expression[::-1]:
if c == ')': operator.append(c)
elif c == '(':
while operator[-1] != ')': output.append(operator.pop())
operator.pop()
elif c == '^' or c == '/' or c == '*' or c == '+' or c == '-':
if len(operator)>0:
while priority[operator[-1]] > priority[c]:
output.append(operator.pop())
if len(operator) == 0: break
operator.append(c)
else: output.append(c)
if len(operator) > 0:
while len(operator) != 0: output.append(operator.pop())
result = ""
temp = ""
temp2 = []
reachedPrefix = False
for e in output[::-1]:
if e == ' ': continue
temp+=e
for w in temp:
if not reachedPrefix and isDigit(w):
temp2.append(' ')
reachedPrefix = True
temp2.append(w)
temp3 = ""
i = 0
while i != len(temp2):
temp3 += temp2
if temp2 == ' ' or temp2 == '' or not isDigit(temp2): temp3 = ""
if temp3 in elements:
temp2.insert(i+1, ' ')
temp3 = ""
i+=1
del temp, temp3
reachedPrefix = False
j = 0
while j != len(temp2):
if not reachedPrefix and isDigit(temp2[j]):
reachedPrefix = True
j+=1
continue
result+=temp2[j]
j+=1
del temp2
return result
def add_spaces(string: str):
space = ' '
temp = string.split(" ")
string = ""
for e in temp:
if e != '': string+=e
del temp
Lstring = list(string)
for i in range(len(Lstring)*2):
if i%2==0: Lstring.insert(i, space)
string = ""
for e in Lstring: string+=e
return string[1:]

print(to_prefix(input()))


Our teacher is tough and gave us an example and says it should output like so:

#Input: 1-2-33
#output: --1 2 33


I finally managed to do it but the problem is if my teacher thinks to try other numbers and maybe even variables, in some cases its formatting won't look like how he wants. This is what I put in and what I get:

#input: (9-81)*(2+21)
#output: *-9 81 +2 2 1
--> expected: *-9 81 + 2 21


#input: (A-8)*(34+21)
#output: *-A 8 +34 21
--> expected: *-A 8 + 34 21


What changes should be made in the code to get these exact results?

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