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
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.
DataCamp
datacamp.com › tutorial › do-while-loop-python
Emulating a Do-While Loop in Python: A Comprehensive Guide for Beginners | DataCamp
January 31, 2024 - Python does not have a built-in "do-while" loop, but you can emulate its behavior.
How can I emulate a do-while loop in Python? - Python - Data Science Dojo Discussions
In other languages like C, I could use a do-while loop to accomplish this, but it seems that Python does not have a built-in equivalent. I’ve tried using a while loop with a flag variable, but I’m not sure if this is the most Pythonic way to do it. Can someone suggest a more elegant solution? More on discuss.datasciencedojo.com
1
1
March 5, 2023python - How to emulate a do-while loop? - Stack Overflow
I need to emulate a do-while loop in a Python program. Unfortunately, the following straightforward code does not work: list_of_ints = [ 1, 2, 3 ] iterator = list_of_ints.__iter__() element = None More on stackoverflow.com
Need help understanding this while loop
I’m new to while loops, and I don’t quite get what’s going on in this code from my book: current_number = 1 while current_number More on discuss.python.org
0
February 13, 2024How 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
Python While Loops & For Loops | Python tutorial for Beginners
02:54
Python Emulating a Do While Loop - YouTube
While loops in Python are easy! ♾️
05:40
While Loops in Python | Python for Beginners - YouTube
24:46
Loops in Python | For, While, Do While Loops | Python Course | ...
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 - A do-while loop is a loop that executes a block of code at least once, then checks a boolean condition which results in a true or false to decide whether to repeat the block of code or not.
Data Science Dojo
discuss.datasciencedojo.com › python
How can I emulate a do-while loop in Python? - Python - Data Science Dojo Discussions
March 5, 2023 - I’m trying to write a program in Python that requires a loop to execute at least once before checking a condition to see if the loop should continue. In other languages like C, I could use a do-while loop to accomplish this, but it seems that Python does not have a built-in equivalent.
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 ...
W3Schools
w3schools.com › python › python_while_loops.asp
Python While Loops
With the break statement we can stop the loop even if the while condition is true: ... Note: The else block will NOT be executed if the loop is stopped by a break statement. ... If you want to use W3Schools services as an educational institution, team or enterprise, send us an e-mail: sales@w3schools.com · If you want to report an error, or if you want to make a suggestion, send us an e-mail: help@w3schools.com · HTML Tutorial CSS Tutorial JavaScript Tutorial How To Tutorial SQL Tutorial Python Tutorial W3.CSS Tutorial Bootstrap Tutorial PHP Tutorial Java Tutorial C++ Tutorial jQuery Tutorial
freeCodeCamp
freecodecamp.org › news › python-do-while-loop-example
Python Do While – Loop Example
August 31, 2021 - If the number the user submits is negative, the loop will keep on running. If it is positive, it will stop. Python does not have built-in functionality to explicitly create a do while loop like other languages.
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.
Real Python
realpython.com › python-while-loop
Python while Loops: Repeating Tasks Conditionally – Real Python
March 3, 2025 - However, translating the for loop ... ... A do-while loop is a control flow statement that executes its code block at least once, regardless of whether the loop condition is true or false....
Coursera
coursera.org › tutorials › python-while-loop
How to Write and Use Python While Loops | Coursera
A do while loop is a variant of the while loop that checks the condition at the end of the loop rather than the beginning. Even if the condition is never true, the statements inside the loop body will be executed at least once. do while loops ...
Texas Instruments
education.ti.com › en › resources › computer-science-foundations › do-while-loops
Python coding: Do While Loops | Texas Instruments
Explore Do While loops in Python on the TI-Nspire™ CX II graphing calculator. Do While loops are a form of post-test loop that always run at least one time.
Python.org
discuss.python.org › python help
Need help understanding this while loop - Python Help - Discussions on Python.org
February 13, 2024 - I’m new to while loops, and I don’t quite get what’s going on in this code from my book: current_number = 1 while current_number <= 5: print(current_number) current_number += 1 After just watching a video on Yo…
Reddit
reddit.com › r/learnpython › how do while not loops work
r/learnpython on Reddit: How do while not loops work
September 11, 2024 -
I was reading through this code and I'm just not getting how while loops work when not operator is also used.
https://pastebin.com/5mfBhQSb
I thought the not operator just inversed whatever the value was but I just can't see this code working if that's the case.
For example , the while not sequenceCorrect should turn the original value of False to True, so the loop should run while it's True. But why not just state while True then? And why declare sequenceCorrect = True again? Doesn't it just means while True, make it True? And so on.
The only way it makes sense to me is of the while not loop always means False (just like the while always means as long as it's True) even if the value is supposed be False and should be inverted to True.
So, is that the case? Can anyone explain why it works like that?
Top answer 1 of 8
7
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.
2 of 8
2
The difference here is that by using not sequenceCorrect you are avoiding the use of the break keyword. It's cleaner and makes the loop terminate itself, rather than relying on a specific keyword and force terminate it. You could use while True, but that way is not descriptive enough and can potentially create and endless loop if you don't take care of the edge cases. Think about it: while not sequenceCorrect is telling you, without a single comment line, that the loop should run while sequenceCorrect is False, vs while True which the only thing that's telling you is that this loop will run endlessly for unknown reasons.
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
Quora
quora.com › How-do-I-use-for-and-while-loops-in-Python
How do I use for and while loops in Python?
Answer (1 of 10): > [[ Warning: this answer is for beginners and learners. . . . Proficient programmers need not read. ]] —— It’s day ten on planet Uiton. Jan and two colleagues set out in their spaceships, early in the morning, but by noon, something had hit Jan’s ship, causing it to crash-...
Python.org
discuss.python.org › python help
Help Understanding While loops - Python Help - Discussions on Python.org
November 3, 2023 - Hello, I have been learning python using Solo learn. It has been a good source for me. I have made it to this point once and I restarted the course again. I am stuck at loops again. This seems to be an important part. If anyone could help me understand what is happening in this line of code I would appreciate it. counter = 0 while counter
Alma Better
almabetter.com › bytes › tutorials › python › while-loop-in-python
While Loop in Python
October 2, 2024 - The Python While Loop 🔁 repeatedly executes a block of statements until a specified condition :thinking: becomes false. Once the condition becomes false, the first line after the Loop executes.
Quora
quora.com › When-how-do-you-use-a-for-loop-and-a-while-loop-in-Python
When/how do you use a for loop and a while loop in Python? - Quora
In Python, a for loop iterates (i.e. runs the code) over a collection (an iterable), while a while loop iterates while a condition is met. What is a collection? It’s just a group of things.
Python documentation
docs.python.org › 3 › tutorial › controlflow.html
4. More Control Flow Tools — Python 3.14.3 documentation
In a for loop, the else clause is executed after the loop finishes its final iteration, that is, if no break occurred. In a while loop, it’s executed after the loop’s condition becomes false.
Hackr
hackr.io › home › articles › programming › python
Python Do While | Docs With Examples
February 12, 2025 - Python does not have a built-in do-while loop like some other languages (e.g., C, Java).