TypeError:'str' object is not callable error in Python entry

I started to learn some practical functions of python today, and reported TypeError:'str' object is not callable error when using the str() method

Below is my code

>>> x=1.235
>>> int(x)
1
>>> str="fsgavfdbafdbntsbgbt"
>>> len(str)
19
>>>
>>> x=987456123
>>> str(x)

Then it reported an error

I checked the information and found that it was because I had defined the str variable above. After the definition, the str() method below became uncallable.