There's no prepackaged "do-while", but the general Python way to implement peculiar looping constructs is through generators and other iterators, e.g.:
import itertools
def dowhile(predicate):
it = itertools.repeat(None)
for _ in it:
yield
if not predicate(): break
so, for example:
i=7; j=3
for _ in dowhile(lambda: i<j):
print i, j
i+=1; j-=1
executes one leg, as desired, even though the predicate's already false at the start.
It's normally better to encapsulate more of the looping logic into your generator (or other iterator) -- for example, if you often have cases where one variable increases, one decreases, and you need a do/while loop comparing them, you could code:
def incandec(i, j, delta=1):
while True:
yield i, j
if j <= i: break
i+=delta; j-=delta
which you can use like:
for i, j in incandec(i=7, j=3):
print i, j
It's up to you how much loop-related logic you want to put inside your generator (or other iterator) and how much you want to have outside of it (just like for any other use of a function, class, or other mechanism you can use to refactor code out of your main stream of execution), but, generally speaking, I like to see the generator used in a for loop that has little (ideally none) "loop control logic" (code related to updating state variables for the next loop leg and/or making tests about whether you should be looping again or not).