When I try to modify string using += operator, and use id() method to check object's identity, string seems to be mutable. Did someone face with such a weird python behaviour?
a = '123'
print id(a)
# 89806008
a += '1'
print id(a)
# 89245728
a += '1'
print id(a)
# 89245728
print a
# '12311'
Using a = a + '1' doesnt have the same effect, and change the string id.
If you were correct about this string being mutable, then adding
b = a
before your second a += '1' should not have any effect on your output. But it does.
The reason is that because the string a had before the "increment" is no longer used anywhere, the id can be re-used. But by assigning that string to b, it now is used somewhere, and the new string for a can't re-use that id.