how do i solve python allocation problem with cnt =+1

I'm new to python and trying to sort scores in descendant order and see if who got the same score. Here's the code

Score = [90, 80, 92, 88, 75, 88, 80, 80, 90, 90, 90, 75]
Score.sort(reverse=True)
sorted_unique_score = []

#sorting in desc order
for score in Score:
  if score not in sorted_unique_score:
    sorted_unique_score.append(score) 

#find the same scores
for unique_score in sorted_unique_score:
  cnt = 0
  for score in Score:
    if unique_score == score:
      cnt = cnt + 1 # somehow this one doesn't work -->  cnt =+ cnt 1
    else:
      continue

  if cnt == 1:
    print(f"for {unique_score}: is a unique score")  
  else:
    print(f"for {unique_score} : {cnt} students got the same score")

this works perfectly but I'm wondering why this one below doesn't work.

Score = [90, 80, 92, 88, 75, 88, 80, 80, 90, 90, 90, 75]
Score.sort(reverse=True)
sorted_unique_score = []

#sorting in desc order
for score in Score:
  if score not in sorted_unique_score:
    sorted_unique_score.append(score) 

#find the same scores
for unique_score in sorted_unique_score:
  cnt = 0
  for score in Score:
    if unique_score == score:
      cnt =+ cnt 1 
    else:
      continue

  if cnt == 1:
    print(f"for {unique_score}: is a unique score")  
  else:
    print(f"for {unique_score} : {cnt} students got the same score")

the only difference is cnt =+ cnt +1 part

You should write like this: cnt += cnt 1 and not like : cnt =+ cnt 1