There is no do...while loop because there is no nice way to define one that fits in the statement: indented block pattern used by every other Python compound statement. As such proposals to add such syntax have never reached agreement.
Nor is there really any need to have such a construct, not when you can just do:
while True:
# statement(s)
if not condition:
break
and have the exact same effect as a C do { .. } while condition loop.
See PEP 315 — Enhanced While Loop:
Rejected […] because no syntax emerged that could compete with the following form:
while True:
<setup code>
if not <condition>:
break
<loop body>
A syntax alternative to the one proposed in the PEP was found for a basic do-while loop but it gained little support because the condition was at the top:
do ... while <cond>:
<loop body>
or, as Guido van Rossum put it:
Please reject the PEP. More variations along these lines won’t make the language more elegant or easier to learn. They’d just save a few hasty folks some typing while making others who have to read/maintain their code wonder what it means.