While Loop continues even if the condition has been met (using Python)

Question

This is my code:

while True: 
 chosenUser = raw_input("Enter a username: ")
 with open("userDetails.txt", "r") as userDetailsFile: 
 for line in userDetailsFile:
 if chosenUser in line:
 print "\n"
 print chosenUser, "has taken previous tests. "
 break
 else:
 print "That username is not registered."

Even after entering a username and it outputting results, the loop continues and asks me to input the username again.

I have recently asked a similar question but got it working myself. This one is not working no matter what I try.

Any ideas how to fix it?

Note: userDetailsFile is a text file that is in the program earlier.

The problem might be obvious but I'm quite new to Python so I'm sorry if I'm wasting anyone's time.

• roganjosh: break applies to the for loop and terminates it early. It does not affect the while True loop.

Answer 1

As others have noted, the primary problem is that the break only breaks from the inner for loop, not from the outer while loop, which can be fixed using e.g. a boolean variable or return.

But unless you want the "not registered" line to be printed for every line that does not contain the user's name, you should use for/else instead of if/else. However, instead of using a for loop, you could also just use next with a generator expression to get the right line (if any).

while True: 
 chosenUser = raw_input("Enter a username: ")
 with open("userDetails.txt", "r") as userDetailsFile:
 lineWithUser = next((line for line in userDetailsFile if chosenUser in line), None)
 if lineWithUser is not None:
 print "\n"
 print chosenUser, "has taken previous tests. "
 break # will break from while now
 else:
 print "That username is not registered."

Or if you do not actually need the lineWithUser, just use any:

while True: 
 chosenUser = raw_input("Enter a username: ")
 with open("userDetails.txt", "r") as userDetailsFile:
 if any(chosenUser in line for line in userDetailsFile):
 print "\n"
 print chosenUser, "has taken previous tests. "
 break # will break from while now
 else:
 print "That username is not registered."

This way, the code is also much more compact and easier to read/understand what it's doing.

• Programmer12: That seems quite complex and I'm unfamiliar with this. I'm getting a syntax error in: lineWithUser = next((line in userDetailsFile if chosenUser in line), None) The syntax error is the line) brcaket.
• tobias_k: @Programmer12 There was a mistake in the next generator; however, on closer inspection you don't even need it, any is enough, making it much simpler.

Answer 2

The easiest way to work around this is to make the outer while alterable by using a boolean variable, and toggling it:

loop = True
while loop:
 for x in y:
 if exit_condition:
 loop = False
 break

That way you can stop the outer loop from within an inner one.

Answer 3

The break breaks out the the inner for loop only. Better put everything in a function and stop your while loop with a return:

def main():
 while True: 
 chosenUser = raw_input("Enter a username: ")
 with open("userDetails.txt", "r") as userDetailsFile: 
 for line in userDetailsFile:
 if chosenUser in line:
 print "\n"
 print chosenUser, "has taken previous tests. "
 return # stops the while loop
 print "That username is not registered."
main()
print 'keep going here'

• Programmer12: That seems to completely end my whole program though even if I have functions after it?
• tobias_k: This will not work properly, if else should actually be after the for (to execute if the for finished normally) but that won't work with return.
• Mike Müller: @Programmer12 Why should it exit your program? You can write code after main(). You can also use different name than main if you prefer.
• Programmer12: No, sorry. It's still completely ending my program. (I'm using Python 2.7 if that has anything to do with it?)
• Programmer12: I have this after my code: ` print "\n", "You can now exit the quiz or choose another report." while True: userDecision = raw_input("Choose 'report' or 'exit'").lower() if userDecision == 'report': chooseReport() break elif userDecision == "quit": sys.exit()`