all(isinstance(n, int) for n in lst)
Demo:
In [3]: lst = (1,2,3)
In [4]: all(isinstance(n, int) for n in lst)
Out[4]: True
In [5]: lst = (1,2,'3')
In [6]: all(isinstance(n, int) for n in lst)
Out[6]: False
Instead of isinstance(n, int)
you could also use type(n) is int