A confusion related to index of for loop.

indexquestion.py

'''The code is meant to skip adding the character "a" and any other character that comes after "a". For this, I check if string's [i th] index = a, and add 1 to index, so that new index will be able to skip the character coming after "a". But this does not seem to be happening. Why is it so ?'''

str1 = "abcde"
str2 = ""
for i in range(len(str1)):
  if str1[i] == "a":
    i +=1
    continue
  else:
    str2 += str1[i]
print (str2)

#Output is bcde. But why ?