So I have a while true loop -
while True:
getStatus()
print('Ended')
I hope to be able to break out of it if answer is 999. this is what I tried:
def getStatus():
answer = input('What is the box ID? ')
if answer == 999:
return False
elif type(answer) == int:
boxId = answer + 1
print(boxId)
However even when the input is '999' it loops back and asks 'What is the box ID? ' again.
How do I get out of the while true loop?
Your while loop keeps looping because that's exactly what you've told it to do. After the function you call from its body returns, you ignore the return value, unconditionally print "Ended" and then do it all again, since the condition on the loop is obviously still truthy.
If you want the function to control if the loop keeps going, you should use its return value as the condition in the loop, with something like this:
running = True
while running:
running = getStatus()
print("Ended") # move this outside the loop!
This requires that getStatus returns a truthy value when you want to keep looping and a falsey value when you want to stop. Your current implementation of that function doesn't do that. It returns False when 999 is entered, but doesn't explicitly return anything if you give other input (which in Python is equivalent to returning None). Since both False and None are falsey, the code above won't actually work (you could patch it with something like running = getStatus() is None, but that would be horrible). You should change the function to have an explicit return statement in all of its branches (including the case for non-integer inputs, where it doesn't go into either your if or elif blocks).
If the loop and the function's logic are tightly intertwined, it might make sense to move the loop into the function itself, rather than having it be separate and needing to use a return value to signal when to stop. In a single function, you can use break to exit a loop directly:
def getStatus():
while True:
answer = input('What is the box ID? ')
if answer == 999:
break
elif isinstance(answer, int): # isinsance() is better than type(...) == ...
boxId = answer + 1
print(boxId)
else:
print("I'm sorry, I didn't understand that.") # still good to handle this case
you can add if statement before get_status() that will check if it's true and break and in the get_status function you will have to return true to break
def getStatus():
answer = input('What is the box ID? ')
if answer == 999:
return True
elif type(answer) == int:
boxId = answer + 1
print(boxId)
while True:
if getStatus():
print('Ended')
break
def selectedCountry():
while True:
country = input("Enter country of which you want to check pictures HR, RS, RO: ").upper()
if country == str("HR") or country == str("RO") or country == str("RS"):
break
else:
print("Please enter HR or RO or RS: " + "you wrote: " + country)
Why while True is working outside of a function and inside the same problem with asking again
Enter country of which you want to check pictures HR, RS, RO: >? hr
Enter country of which you want to check pictures HR, RS, RO:
You may change it to -
while True:
if(getStatus()==False):
print('Ended')
break
By this you can use returned value to break out of infinite loop.
Related
The question I have is about the flag I have here for the while loop. This works but not like I think it should. I assume I'm not understanding something so if someone is able to explain, that would be great.
From my understanding this should break out of the loop as soon as one of my conditionals is met. So if I input 'q' it should break out and stop the loop. But what happens is it keeps going through the loop and then it breaks out. so it goes through the last prompt and prints the exception.
(Python version is 3.8.5)
# Statement that tells the user what we need.
print("Enter two numbers and I will tell you the sum of the numbers.")
# Lets the user know they can press 'q' to exit the program.
print("Press 'q' at anytime to exit.")
keep_going = True
# Loop to make the program keep going until its told to stop.
while keep_going:
# Prompt for user to input first number and store it in a variable.
first_number = input("First number: ")
# Create a break when entering the first number.
if first_number == 'q':
keep_going = False
# Prompt for user to input second number and store it in a variable.
second_number = input("Second number: ")
# Create a break when entering the second number.
if second_number == 'q':
keep_going = False
# Exception for non integers being input "ValueError"
try:
# Convert input to integers and add them.
# storing the answer in a variable.
answer = int(first_number) + int(second_number)
except ValueError:
# Tell the user what they did wrong.
print("Please enter a number!")
else:
# Print the sum of the numbers
print(f"\nThe answer is: {answer}")
Using this code it breaks out right away like I expect it to.
while True:
first_number = input("First number: ")
if first_number == 'q':
break
second_number = input("Second number: ")
if second_number == 'q':
break
I just would like to understand what the difference is and if thats how it should work. I feel like I'm missing something or misunderstanding something.
The condition of the while loop is only checked between iterations of the loop body, so if you change the condition in the middle of the loop, the current iteration will finish before the loop terminates. If you want to break a loop immediately, you need to either break (which automatically breaks the loop regardless of the condition) or continue (which jumps to the next iteration, and will therefore terminate the loop if the condition is no longer true).
Using while True: with a break when you want to stop the loop is generally much more straightforward than trying to control the loop by setting and unsetting a flag.
FWIW, rather than copying and pasting the code to input the two numbers, and have two different ways to break out of the loop, I might put that all into a function and break the loop with an Exception, like this:
print("Enter two numbers and I will tell you the sum of the numbers.")
print("Press 'q' at anytime to exit.")
def input_number(prompt: str) -> int:
"""Ask the user to input a number, re-prompting on invalid input.
Exception: raise EOFError if the user enters 'q'."""
while True:
try:
number = input(f"{prompt} number: ")
if number == 'q':
raise EOFError
return int(number)
except ValueError:
print("Please enter a number!")
while True:
try:
numbers = (input_number(n) for n in ("First", "Second"))
print(f"The answer is: {sum(numbers)}")
except EOFError:
break
This makes it easier to extend the program to handle more than two inputs; try adding a "Third" after where it says "First" and "Second"! :)
Once you run the program and type "q", Yes indeed keep_going will be set to False but it DOES NOT MEAN it will break the loop already, it will just make the keep_going be equal to False thus on the NEXT ITERATION will stop the loop. Why is that? because it would be like this while keep_going: -> while False: so since it is not True thus not executing the program anymore.
Now based on your goal as you mentioned. You can do it this way where you can add the break.
if first_number == 'q':
keep_going = False
break
# Prompt for user to input second number and store it in a variable.
second_number = input("Second number: ")
# Create a break when entering the second number.
if second_number == 'q':
keep_going = False
break
I'd also like to suggest have it this way, it's just more specific in terms of what is to happen on the code, but of course it is up to you.
first_number = input("First number: ")
# Create a break when entering the first number.
if first_number == 'q':
keep_going = False
break
# Prompt for user to input second number and store it in a variable.
# Create a break when entering the second number.
else:
second_number = input("Second number: ")
if second_number =='q':
keep_going = False
break
While loops execute until their given condition is false. A loop will only check its condition when required (program execution is moved to the top of the loop). In almost every case, this occurs when the full body of the loop has run. See here:
keep_going = True
while keep_going:
keep_going = False
# keep_going is False, but this will still print once
# because the loop has not checked its condition again.
print("Will execute once")
"Will execute once" prints a single time even after keep_going is set to False. This happens because the while loop does not re-check its condition until its entire body has run.
However, break statements are different. A break statement will cause a loop to exit immediately no matter what.
keep_going = True
while keep_going:
break # Exits the while loop immediately. The condition is not checked.
print("Will never print")
Here, nothing is printed even though keep_going is True the whole time. break made the loop exit regardless of the condition.
A continue statement will move program execution back to the start of the loop, and cause your condition to be checked again.
In this example, continue sends program execution back to the start of the loop. Since keep_going was set to False, nothing will print because the while loop will exit after realizing its condition evaluates to false.
keep_going = True
while keep_going:
keep_going = False
continue
print("Will never print")
First off, hope you have a great time learning Python!
Both ways will work and stop the loop, but there is a difference:
In the first method, you are changing the keep_going variable to false, therefore, the loop will stop when the the while loops finds out that keep_going had become False. However, the checking only happens at the end of the loop (In your case, it is after you have done your except or else part), the loop will not stop right away even when you entered q for your variable first_number.
In the second solution, you are using the break keyword in Python, to break away from the loop right away after you entered q for first_number.
Technically speaking, you will want to break if you want to break off from the loop right away when q is detected, otherwise, setting keep_going to False if you want the whole loop to be completed, but not run again for the next round.
In scenario 1 the result, even when you entered q,
Please enter a number!
Will always show, but not for scenario 2.
this is a little different approach to your script:
def main():
print("Enter two numbers and I will tell you the sum of the numbers.")
print("Press 'q' at anytime to exit.")
val = []
while True:
check_value = lambda x: 'quit' if x.lower() == 'q' or x.lower() == 'quit' else int(x)
if not val:
value = input("First number: ")
elif len(val) == 2:
answer = sum(val)
print(f"\nThe answer is: {answer}")
print('==='*15 + ' < ' + f'PROGRAM RESTARTING' + ' > ' + '==='*15)
val[:] = []
continue
else:
value = input("Second number: ")
try:
check_ = check_value(value)
val.append(check_)
except ValueError:
print("Please enter a number!")
continue
finally:
if check_ == 'quit':
print('Program is stopping....')
break
else:
pass
if __name__ == '__main__':
main()
It check at anytime the user's input, whether is a 'q' 'Q' or ('quit' or 'QUIT') or any combination or capital letter because run the check x.lower()
I suggest you to have a look at realpython.com especially the paragraph "he Python break and continue Statements."
Long story short:
Use Break to terminate the loop at any given time.
Use continue to roll back where you left and repeat the loop again (I used it in my code if the value is not a Int)
User pass to keep the loop running with no stop.
I have a problem in a simple code with while loop. My problem is explained in code comments.
CODE
exit = False
while not exit:
choice = input("Test ")
if choice== 1:
print "hello"
exit = False
else:
print "good morning"
#I want to return to the first while with the input Test but I pass to the second while
exit = False
exit1 = False
while not exit1:
choice = input("Test 1")
if choice== 1:
print "bye"
exit1 = False
else:
print "good evening"
#I want to return to the first while with the input Test but I return to the second while
exit = False
Thanks a lot.
I think what are you looking for are the continue and break statements.
The continue will interrupt the current iteration (and a new iteration is started, of course).
The break will interrupt the smallest enclosing loop.
Both statements work for for as well.
Take a look here for some reference.
outer = True
while outer:
do_something
if a:
continue # will get you back to do_something
if b:
break # will end the outer loop
If you set outer to False somewhere, it will end the while loop in the next iteration.
I am new to programming and so i'm practicing a bid. At this point i'm practicing with functions. In the code below break and continue are outside the loop i can not see why. I've tryed out different ways but the only thing i get to work is the last block of code. Why are break and continue outside the loop here?
import random
again = 'y'
while again == "y" :
def main():
print "gues a number between 0 - 10."
nummer = random.randint(1,10)
found = False
while not found:
usergues = input("your gues?")
if usergues == nummer:
print 'Your the man'
found = True
else:
print 'to bad dude try again'
main()
again = raw_input('would you like to play again press y to play again press n yo exit')
if again == 'n':
break #here it says it is outside the loop
elif again != 'y':
print 'oeps i don\'t know what you mean plz enter y to play again or n to exit'
else:
continue #this is outside loop as well
#main()
Because you are new to programming, I will get a few basic tips in my answer too.
INFINITE LOOP
You are trying to start an infinite loop by first settingagain = 'y' and afterwards you are using this variable to evaluate a while loop. Because you are not changing the value of y, it is better to not use a variable to create this infinite loop. Instead, try this:
while True:
(some code)
DEFINE FUNCTION IN LOOP
You're defining the function main() inside of the while loop. As far as I can tell, there is no use for that. Just leave out the first while loop. If you define a function, it is permanent (much like a variable), so no need to redefine it everytime. Using your code, you won't even get to call the function, because you never end the first loop.
CONTINUE/BREAK NOT IN LOOP
The error is quite self-explanaitory, but here we go. If you would ever end the first loop (which in this case, you won't), the next thing you do is call your function main(). This will generate a number and make the user guess it until he got it right. When that happens, you get out of that function (and loop).
Next, you ask if the user would like to play again. This is just an input statement. You store the answer in the variable 'again'. You check, with an if statement (note that this is not a loop!) what the answer is. You want the user to play again if he typed 'y', so instead of using again != 'y', you could use the following:
if again == 'y':
main() # you call the function to play again
If 'n' was typed in, you want to exit the script, which you do not by typing break, because you are not in a loop, just in an if-statement. You can either type nothing, which will just go out of the if-statement. Because there is nothing after the if, you will exit the script. You could also useexit(), which will immediately exit the script.
Lastly, you want to repeat the question if neither of these two things were answered. You can put the if-statement inside of a loop. You can (if you want) use your break and continue when doing this, but you mostly want to avoid those two. Here is an example:
while True:
again = raw_imput('y for again or n to stop')
if again == 'y':
main()
exit() # use this if you don't want to ask to play again after the 2nd game
elif again == 'n':
print('bye!')
exit()
# no need for an 'else' this way
# every exit() can be replaced by a 'break' if you really want to
BASIC BREAK/CONTINUE USAGE
Finally, here is some basic usage of break and continue. People generally tend to avoid them, but it's nice to know what they do.
Using break will exit the most inner loop you are currently in, but you can only use it inside of a loop, obviously (for-loops or while-loops).
Using continue will immediately restart the most inner loop you are currently in, regardless of what code comes next. Also, only usable inside of a loop.
EVERYTHING TOGETHER
import random
again = 'y'
def main():
print ("gues a number between 0 - 10.")
nummer = random.randint(1,10)
found = False
while not found:
usergues = input("your gues?")
if usergues == nummer:
print ('Your the man')
found = True
else:
print ('to bad dude try again')
main()
while True:
again = input('would you like to play again press y to play again press n yo exit')
if again == 'n':
print ('bye!')
exit() # you could use break here too
elif again == 'y':
main()
exit() # you can remove this if you want to keep asking after every game
else:
print ('oeps i don\'t know what you mean plz enter y to play again or n to exit')
I hope I helped you!
You loops and def are all muddled, you want something more like:
import random
again = 'y'
while again == "y" :
print "gues a number between 0 - 10."
nummer = random.randint(1,10)
found = False
while not found:
usergues = input("your gues?")
if usergues == nummer:
print 'Your the man'
found = True
else:
print 'to bad dude try again'
while True:
again = raw_input('would you like to play again press y to play again press n to exit')
if again == 'n':
break
elif again != 'y':
print 'oeps i don\'t know what you mean plz enter y to play again or n to exit'
else:
break
You may want to refer to instructional material because you seem to misunderstand the general purpose of functions and the order of your logic.
Your function should be at the outer scope, e.g.:
def main():
again = 'y'
while again == "y" :
Your question for again needs to be indented into the while loop:
while again == "y":
[snip]
again = raw_input('would you like to play again press y to play again press n to exit')
if again == 'n':
break #here it says it is outside the loop
elif again != 'y':
print 'oops i don\'t know what you mean plz enter y to play again or n to exit'
else:
continue #this is outside loop as well
The else: continue is unnecessary because you are at the end of the loop.
However, this only asks the question once, and you probably want this in a while loop. You also don't need to check the again == "y" in the outer while loop, because you are controlling the flow here:
while True:
[snip]
again = raw_input("would you like to play again press y to play again press n to exit")
while again not in ('y', 'n'):
again = raw_input("oops i don't know what you mean plz enter y to play again or n to exit")
if again == 'n':
break
I would recommend against using a bare input() because any code could be executed, receiving a string and casting to an int would be safe (and you probably do some error checking):
usergues = int(raw_input("your guess?"))
Putting it all together it looks like:
def main():
while True:
print "guess a number between 1 - 10."
nummer = random.randint(1,10)
found = False
while not found:
usergues = int(raw_input("your guess?"))
if usergues == nummer:
print 'You're the man'
found = True
else:
print 'Too bad dude try again'
again = raw_input('would you like to play again press y to play again press n to exit')
while again not in ('y', 'n'):
again = raw_input('oops i don\'t know what you mean plz enter y to play again or n to exit')
if again == 'n':
break
main()
I started learning to code this week so I'm playing around with small programs that I'm creating to try to get a better understanding of how it work.
One of the programs I made is a Pig Latin translator that loops until the user exits. The program works but the logic isn't making any sense to me.
pyg = "ay" #Pig Latin words end with ay.
def translate(): #Creating a function.
original = input("Enter a word: ").lower() #Ask for input then convert to lower.
if len(original) > 0 and original.isalpha() : #isalpha() verifies only abc's and more than one letter.
first = original[0] #Assigns the first letter of the string to first.
latin = original[1:] + first + pyg #Adds original starting at 2nd letter with first and pyg.
print(latin)
else:
print("You did not enter a valid word, please try again.")
translate() #If you did not enter valid word, then call function again until you do.
translate() #Don't forget to actually call the function after you define it.
#Set run to False.
#Can be set to True if while (run != True) is set to while (run == True).
run = False
#Defining cont(). Ask for imput and error handling.
def cont():
loop = input("Would you like to convert another word? (y/n): ").lower()
if loop == "y" :
run = True
elif loop == "n" :
run = False
print("Thank you for using this program, have a nice day!")
exit()
else :
print("You did not enter a valid response, please try again.")
cont()
cont()
#Infinite loop as long as run is not equal to True.
while (run != True) :
translate()
cont()
My question is, why does this program work? I set run to False and I set the loop to run as long as run != True. No problem there, however when I defined cont(), I set run to take on the value True if the user inputs "y". True != True should be False (if I understand correctly) and the loop should end, but instead it is working as I wanted it to.
Is this a coding mistake that I've made or am I just thinking about this the wrong way? Thank you in advance.
Edit: Thank you very much to everyone that answered. I hadn't learned about local and global variables yet.
To expand on what others have already stated, run on these lines
if loop == "y" :
run = True
elif loop == "n" :
run = False
are not referring to the same run defined by
#Can be set to True if while (run != True) is set to while (run == True).
run = False
run in the cont function is a local variable to your function, not the globaly defined run.
There are a couple (at least) ways to fix this. The preferred (imo) way to do it is have cont return a new value to be assigned to run. That would look like
#Defining cont(). Ask for imput and error handling.
def cont(_run):
loop = input("Would you like to convert another word? (y/n): ").lower()
if loop == "y" :
return _run
elif loop == "n" :
return not _run
else :
print("You did not enter a valid response, please try again.")
return cont(_run)
...
#Infinite loop as long as run is not equal to True.
while (run != True) :
translate()
run = cont(run)
The other (less preferred) way would be to use the global run variable inside of your cont function. This is achieved using the global keyword.
That would look like this:
#Defining cont(). Ask for imput and error handling.
def cont():
global run
loop = input("Would you like to convert another word? (y/n): ").lower()
if loop == "y" :
run = True
elif loop == "n" :
run = False
print("Thank you for using this program, have a nice day!")
exit()
else :
print("You did not enter a valid response, please try again.")
cont()
** Couple side notes
In my first example I return _run when the value is y and not _run when the value is n. This allows you to change you initial run value to be True, and change the while condition without having to change the cont function itself.
You don't need to actually change the run value at all if you use the global and the user enters n since you exit before the function returns.
You might be better off changing your if conditional checks to
if loop in ("yes", "y"):
if loop in ("no", "n"):
since lots of people don't read full instructions :)
The run inside the cont function is a local variable. Changing its value has no effect on the global variable that the while loop refers to.
I think this is probably because of the scope of your run variable; because you're not returning run from your cont function. I believe what your != True check sees is always going to be False outside of that function, though obviously you can successfully end the program within the function.
The problem is that the run variable defined in cont() is not the same as the run variable defined in the global scope. (If you aren't sure what I mean by that you might want to look at https://docs.python.org/3.4/tutorial/classes.html#python-scopes-and-namespaces. Perhaps a better approach for your code would be to have cont() return True or False. It is also more intuitive and readable to use True for when you want to continue. Here's how I would rewrite it.
pyg = "ay" #Pig Latin words end with ay.
def translate(): #Creating a function.
original = input("Enter a word: ").lower() #Ask for input then convert to lower.
if len(original) > 0 and original.isalpha() : #isalpha() verifies only abc's and more than one letter.
first = original[0] #Assigns the first letter of the string to first.
latin = original[1:] + first + pyg #Adds original starting at 2nd letter with first and pyg.
print(latin)
else:
print("You did not enter a valid word, please try again.")
translate() #If you did not enter valid word, then call function again until you do.
#Defining cont(). Ask for imput and error handling.
def cont():
while True:
loop = input("Would you like to convert another word? (y/n): ").lower()
if loop == "y":
return True
elif loop == "n":
print("Thank you for using this program, have a nice day!")
return False
else :
print("You did not enter a valid response, please try again.")
translate()
while cont():
translate()
I simply cannot understand what is happening here. The problem is important for my homework (studying programming so I'm a beginner... also my English is not that good, sorry).
I am trying to read a string... it can be either a number or a set number of commands.
I'll just give a very small example of what I'm trying to do and what is going wrong.
def validate():
choice = str(input(">>> "))
if (choice == "exit"):
return 0 # should exit validate
else:
try:
aux = int(choice) # Tries converting to integer
except:
print("Insert integer or exit")
validate() # If it can't convert, prompts me to try again through
# recursivity
else:
return aux
rezult = validate()
print (rezult)
Problem is that this small script returns totally random stuff.
If "exit", returns "None".
If first input is correct, it returns correct number.
If first input is an "error" and second input is correct, it's "None" again and I simply can't understand what is going wrong... Why it doesn't want to work or what should I do (alternatively).
In case you enter the except block, the function validate() uses a recursive call to call itself. When this call returns, it returns to the place where the function was called, i.e. into the except block. The return value of validate() is ignored at this point, and control reaches the end of the outer call without hitting a return statement, so None is implicitly returned.
Don't use recursion here. Use a loop.
Use raw_input instead of input (unless you are on Python 3.x):
choice = raw_input(">>> ")
And you are missing a return here:
except:
print ("Insert integer or exit")
return validate () # <<< here
Also, don't use recursion for this. Use a loop instead.
Ok, decided to listen and changed the recursive part into a loop, thank you for your help. (Works now)
def validateChoice():
condition = False
while (condition == False):
choice = str (input (">>> "))
if (choice == "exit"):
return 0
else:
try:
aux = int (choice)
except:
print ("Insert integer or 'exit'")
else:
condition = True
return aux