Q:

Is my python generator function really lazy? 

Simple generator function I made:
def myfunc(text):
    for i in text[::-1]:
        yield(i)

for i in myfunc("anytext"):
    print(i)

will text[::-1] inside generator function will be evaluated first or it will be evaluated lazily (expected from generator function) ?  

A:

The text will be reversed before it is iterated over.  It can't be any other way; the for loop needs the reversed text in order to iterate over it. 
To make it truly lazy you'll need to use an index. 
def myfunc(text):
    for i in range(len(text) - 1, -1, -1):
        yield text[i]

In Python 2, use xrange in place of range. 
Of course, you have basically re-implemented the built-in function reversed().