I am not sure what you are trying to do. You can implement a do-while loop like this:
while True:
stuff()
if fail_condition:
break
Or:
stuff()
while not fail_condition:
stuff()
What are you doing trying to use a do while loop to print the stuff in the list? Why not just use:
for i in l:
print i
print "done"
Update:
So do you have a list of lines? And you want to keep iterating through it? How about:
for s in l:
while True:
stuff()
# use a "break" instead of s = i.next()
Does that seem like something close to what you would want? With your code example, it would be:
for s in some_list:
while True:
if state is STATE_CODE:
if "//" in s:
tokens.add( TOKEN_COMMENT, s.split( "//" )[1] )
state = STATE_COMMENT
else :
tokens.add( TOKEN_CODE, s )
if state is STATE_COMMENT:
if "//" in s:
tokens.append( TOKEN_COMMENT, s.split( "//" )[1] )
break # get next s
else:
state = STATE_CODE
# re-evaluate same line
# continues automatically
Top answer 1 of 16
1331
I am not sure what you are trying to do. You can implement a do-while loop like this:
while True:
stuff()
if fail_condition:
break
Or:
stuff()
while not fail_condition:
stuff()
What are you doing trying to use a do while loop to print the stuff in the list? Why not just use:
for i in l:
print i
print "done"
Update:
So do you have a list of lines? And you want to keep iterating through it? How about:
for s in l:
while True:
stuff()
# use a "break" instead of s = i.next()
Does that seem like something close to what you would want? With your code example, it would be:
for s in some_list:
while True:
if state is STATE_CODE:
if "//" in s:
tokens.add( TOKEN_COMMENT, s.split( "//" )[1] )
state = STATE_COMMENT
else :
tokens.add( TOKEN_CODE, s )
if state is STATE_COMMENT:
if "//" in s:
tokens.append( TOKEN_COMMENT, s.split( "//" )[1] )
break # get next s
else:
state = STATE_CODE
# re-evaluate same line
# continues automatically
2 of 16
413
Here's a very simple way to emulate a do-while loop:
condition = True
while condition:
# loop body here
condition = test_loop_condition()
# end of loop
The key features of a do-while loop are that the loop body always executes at least once, and that the condition is evaluated at the bottom of the loop body. The control structure show here accomplishes both of these with no need for exceptions or break statements. It does introduce one extra Boolean variable.
GeeksforGeeks
geeksforgeeks.org › python › python-do-while
Python Do While Loops - GeeksforGeeks
July 23, 2025 - In Python, we can simulate the behavior of a do-while loop using a while loop with a condition that is initially True and then break out of the loop when the desired condition is met.
Why not add do-while loops to Python?
I think the assignment expressions of PEP 572 are being implemented partly because of this. It’s even one of the examples: https://www.python.org/dev/peps/pep-0572/#id22 More on reddit.com
22
3
August 30, 2019As a beginner how do I understand while loops?
It’s just a loop which continues running until the condition becomes false. More on reddit.com
76
36
April 10, 2025How do while not loops work
In general, recall the while loop syntax. while : Conceptually, coding aside, consider filling a glass of water. Is there space for more water in the glass? Okay, then pour some. Without going in detail of how this funky glass object is defined, hopefully the following makes sense as a python analog of that process. while glass.has_space(): #we're still filling the glass glass.add_water() #glass is now full of water Without writing out how this glass object works, let's say it has another method for returning a boolean (True/False) for whether or not it is currently full, instead of the previous example of whether or not it had space for more water. We can fill the glass in the same way, but we have to negate that statement using the not operator while not glass.is_full(): #we're still filling the glass glass.add_water() #glass is now full of water Going back to the initial syntax, which is still the same, the only thing we've done is changing the condition statement of the loop. Instead of checking that glass.has_space() evaluates to True, we are now checking that the expression not glass.is_full() evaluates to True. That is the same statement as evaluating that glass.is_full() evaluates to False, because the only thing the not operator does to a boolean is negating it, i.e. True becomes False and vice versa. Now looking at your code linked, the condition for looping is that not sequenceCorrect evaluates to True, which is equivalent to the statement that sequenceCorrect is False. I won't paste the code here, but we see on line 3 that sequenceCorrect starts its life being False, so upon entering the while loop we do indeed step into that block of code because at that time not sequenceCorrect is in fact True. Then the first thing we do on line 5 is reassign it to True. If the remaining lines don't change it back to False, this will stop the while loop from repeating, since in this current state not sequenceCorrect evaluates to False. So you can say that line 5 is defaulting the loop to not going to be repeated. The only way for the loop to be repeated is for lines 6-8 with the nested for loop and if statement to find some character in dna that is not in "actgn", upon which sequenceCorrect will be assigned to False and thus the statement in the while loop not sequenceCorrect would evaluate to True and thus the loop would repeat itself once more. Personally, I think this is just a pretty unclear way to achieve the goal of checking the validity of that input string. I would have defined it another way, but I can't see anything wrong with it really. If the not operation in the while loop statement is bothering you, you could equally have rewritten the code with a variable for instance named sequenceIncorrect and just flipped all assignments i.e. True's become False's and vice versa. More on reddit.com
16
5
September 11, 2024Videos
03:06
Beginner Python Tutorial 69 - do while Loop in Python - YouTube
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02:54
Python Emulating a Do While Loop - YouTube
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While Loops in Python | Python for Beginners - YouTube
While loops in Python are easy! ♾️
10:12
While Loop in Python (Perform a Task 1000000 times With Ease) #8 ...
W3Schools
w3schools.com › python › python_while_loops.asp
Python While Loops
Python Examples Python Compiler ... Bootcamp Python Certificate Python Training ... With the while loop we can execute a set of statements as long as a condition is true....
freeCodeCamp
freecodecamp.org › news › python-do-while-loop-example
Python Do While – Loop Example
August 31, 2021 - The while loop, on the other hand, doesn't run at least once and may in fact never run. It runs when and only when the condition is met. So, let's say we have an example where we want a line of code to run at least once. secret_word = "python" counter = 0 while True: word = input("Enter the secret word: ").lower() counter = counter + 1 if word == secret_word: break if word != secret_word and counter > 7: break
DataCamp
datacamp.com › tutorial › do-while-loop-python
Emulating a Do-While Loop in Python: A Comprehensive Guide for Beginners | DataCamp
January 31, 2024 - To emulate a "do-while" loop in Python, you can use a while loop with a True condition and strategically place a break statement. Here's an example: while True: # Execute your code here if not condition: break · In this structure, the loop executes at least once.
Reddit
reddit.com › r/python › why not add do-while loops to python?
r/Python on Reddit: Why not add do-while loops to Python?
August 30, 2019 -
It continues to puzzle me why we have no do-while loop in Python.
In Python code, it's common to see the following pattern:
# ... some code ....
while condition:
# ... same code copied here ...This is of course prone to problems because of the "minor" code duplication.
Alternatively, you might see this better option:
def some_code():
# ... some code ...
some_code()
while condition:
some_code()This involves creating a function even though IMHO it often serves to bloat the code unnecessarily.
And than there's this variation:
while True:
# ... do something ...
if not condition:
breakIMHO, this approach, especially when the body of the loop is fairly large, fails to communicate the logical intent of the code in a clean manner.
Of course - all of these approaches do work. But IMHO a syntax which could clarify programmer's intent in the most precise and concise way is the following classical do-while:
do:
# ... do something ...
while some_conditionI know that years ago do-while style constructs have been proposed in PEPs and rejected.
But isn't it time we review the idea again? I think there is a considerable amount of code which could benefit from this.
Would love to hear your thoughts :)
Top answer 1 of 10
7
I think the assignment expressions of PEP 572 are being implemented partly because of this. It’s even one of the examples: https://www.python.org/dev/peps/pep-0572/#id22
2 of 10
6
Honestly in my entire programming career I can't really think of a single instance where I've actually used a do-while loop and I never come across them in the wild either. I personally am not a fan of do-while as I think they're just an unnecessary legacy idea. There's nothing (IMO) that a do-while adds. My guess is Python creators feel the same.
Programiz
programiz.com › python-programming › while-loop
Python while Loop (With Examples)
In Python, we use the while loop to repeat a block of code until a certain condition is met.
Real Python
realpython.com › python-while-loop
Python while Loops: Repeating Tasks Conditionally – Real Python
March 3, 2025 - If you come from languages like C, C++, Java, or JavaScript, then you may be wondering where Python’s do-while loop is. The bad news is that Python doesn’t have one. The good news is that you can emulate it using a while loop with a break statement. Consider the following example, which takes user input in a loop:
Coursera
coursera.org › tutorials › python-while-loop
How to Write and Use Python While Loops | Coursera
February 24, 2023 - There is no do while loop in Python, but you can modify a while loop to achieve the same functionality.
Real Python
realpython.com › python-do-while
How Can You Emulate Do-While Loops in Python? – Real Python
August 2, 2022 - In this tutorial, you'll learn how to emulate do-while loops in Python. The most common technique to do this is to create an infinite while loop with a conditional statement that controls the loop and jumps out of it using a break statement.
Texas Instruments
education.ti.com › en › resources › computer-science-foundations › do-while-loops
Python coding: Do While Loops | Texas Instruments
Note that this loop structure is slightly different than Do While loop structures that appear in other programming languages. Python doesn’t have a built-in Do While loop structure, but the behavior of a Do While loop can be modeled with programs that use While, If and break commands as we’re exploring here.
EDUCBA
educba.com › home › software development › software development tutorials › python tutorial › do while loop in python
Do While Loop in Python | Emulate Do While Loop in Python(Example)
March 17, 2023 - In the python body of the while, the loop is determined through indentation. As there is no proper indentation for specifying do while loop in python, therefore there is no do-while loop in python, but it is done with while loop itself.
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YoungWonks
youngwonks.com › blog › do-while-loop-python
What is a do while loop in Python? How do I create a while loop in Python? What is the difference between a for loop and a while loop in Python?
February 18, 2024 - For instance, if you want to print ... fundamental in any Python tutorial for beginners. There are various types of loops, including the for loop, while loop, and the do-while loop....
Reddit
reddit.com › r/learnpython › as a beginner how do i understand while loops?
r/learnpython on Reddit: As a beginner how do I understand while loops?
April 10, 2025 -
While loops is kinda frustrating I'm 20 days into python and I'm stuck on loops since last 4 days
Javatpoint
javatpoint.com › python-do-while-loop
Python Do While Loop - Javatpoint
Python Do While Loop - The do while loop is used to check condition after executing the statement. It is like while loop but it is executed at least once.
Educative
educative.io › answers › how-to-emulate-a-do-while-loop-in-python
How to emulate a do-while loop in Python
A do-while loop is important because it is a post-test loop, meaning that it checks the condition only after executing the code in the loop block. Even though Python doesn’t explicitly have the do-while loop, we can emulate it. There are two scenarios in which a loop terminates:
Scaler
scaler.com › home › topics › python do while loop
Python Do While Loop - Scaler Topics
December 1, 2023 - Python While Loop is used to execute a block of statements repeatedly until a given condition is satisfied, and when the condition becomes false, the line immediately after the Loop in the program is executed.
Python
wiki.python.org › moin › WhileLoop
While loops - Python Wiki
If a change to this archive is absolutely needed, requests can be made via the infrastructure@python.org mailing list. ... While loops, like the ForLoop, are used for repeating sections of code - but unlike a for loop, the while loop will not run n times, but until a defined condition is no ...
Python Morsels
pythonmorsels.com › while-loops
Python's "while" loop - Python Morsels
June 20, 2025 - But what if you need to perform an operation repeatedly and you don't have an iterable to loop over? In that case, Python has a different kind of loop you could use. Python's while loops are for looping based on a condition.
DaniWeb
daniweb.com › programming › software-development › threads › 39804 › do-while-loop-in-python
do-while loop in python [SOLVED] | DaniWeb
Python does not have a built-in do...while, but you can emulate "run at least once, then decide" cleanly. Use a boolean updated at the end of each iteration (avoid strings like "true"/"false", and prefer logical and over bitwise &): finished ...