You can use the getattr built-in:
>>> import random
>>> variable = 'randint'
>>> getattr(random, variable)(1, 3)
3
>>>
From the docs:
getattr(object, name[, default])
Return the value of the named attribute of object. name must be a string. If the
string is the name of one of the object’s attributes,
the result is the value of that attribute. For example, getattr(x,
'foobar') is equivalent to x.foobar. If the named attribute does not
exist, default is returned if provided, otherwise AttributeError is
raised.