The following are totally acceptable in python:

• passing a string representation of an integer into int
• passing a string representation of a float into float
• passing a string representation of an integer into float
• passing a float into int
• passing an integer into float

But you get a ValueError if you pass a string representation of a float

int("5")
5
float("5.0")
5.0
float("5")
5.0
int(5.0)
5
float(5)
5.0
int("5.0")
Traceback (most recent call last):
  File "<input>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '5.0'