while True:
n = int (input ("What's n? "))
if n > 0:
break
for _ in range(n):
print("meow")
I can enter the input, but I could receive the output and I didn't have any error in my terminal window, please help where I went wrong.
Your for loop is inside your while loop and after the if statement. When your if statement evaluates to True (i.e. n > 0) then the break instruction will cause the program to exit the while loop. Thus, your for loop will never be executed.
You can learn more about the break statement from this tutorial.
The break statement in Python terminates the current loop and resumes
execution at the next statement
You can fix your code by moving the for loop outside of the while loop as follows:
while True:
n = int(input("What's n? "))
if n > 0:
break
for _ in range(n):
print('meow')
Related
I am a beginner in Python and from what I understand, the continue statement in Python returns the control to the beginning of the while loop.
guesses = [0]
while True:
# we can copy the code from above to take an input
guess = int(input("I'm thinking of a number between 1 and 100.\n What is your guess? "))
if guess < 1 or guess > 100:
print('OUT OF BOUNDS! Please try again: ')
continue
# here we compare the player's guess to our number
if guess == num:
print(f'CONGRATULATIONS, YOU GUESSED IT IN ONLY {len(guesses)} GUESSES!!')
break
# if guess is incorrect, add guess to the list
guesses.append(guess)
# when testing the first guess, guesses[-2]==0, which evaluates to False
# and brings us down to the second section
if guesses[-2]:
if abs(num-guess) < abs(num-guesses[-2]):
print('WARMER!')
else:
print('COLDER!')
else:
if abs(num-guess) <= 10:
print('WARM!')
else:
print('COLD!')
Above is the code for the game called 'guess the number from 1 - 100'.
The first if statement where guess < 1 or guess > 100, it will print "Out of bounds!" and then continue which loops to the top of the code and asks for the user's input again.
But for the 3rd if statement where if guesses[-2]:, it does not require continue for neither if nor else.
Sorry if you do not understand what I am asking. But essentially, I want to know why 'continue' statement is not required after print('WARMER!), print('COLDER!'), print('WARM!') and print('COLD!').
guesses = [0]
while True:
# we can copy the code from above to take an input
guess = int(input("I'm thinking of a number between 1 and 100.\n What is your guess? "))
if guess < 1 or guess > 100:
print('OUT OF BOUNDS! Please try again: ')
continue
# here we compare the player's guess to our number
if guess == num:
print(f'CONGRATULATIONS, YOU GUESSED IT IN ONLY {len(guesses)} GUESSES!!')
break
# if guess is incorrect, add guess to the list
guesses.append(guess)
# when testing the first guess, guesses[-2]==0, which evaluates to False
# and brings us down to the second section
if guesses[-2]:
if abs(num-guess) < abs(num-guesses[-2]):
print('WARMER!')
**continue**
else:
print('COLDER!')
**continue**
else:
if abs(num-guess) <= 10:
print('WARM!')
**continue**
else:
print('COLD!')
**continue**
Note that all four of these print statements are the last of their execution branch.
Meaning, if guesses[-2] evaluates as true, than the else part won't be executed at all. Then, if abs(num-guess) < abs(num-guesses[-2]) evaluates to true, again - its else won't be executed. It means that for this execution branch the print('WARMER!') is the last statement of the loop and hence continue is not needed.
Same logic applies to all other 3 print statements.
In the case "guess < 1 or guess > 100" you want to skip the rest of the loop since you dont want to append the guess to the guesses list. Therefore you use continue.
The 'continue' statement is not required after print('WARMER!) etc because you dont need to skip any code afterwards. In this case because there wont be any lines executed after the print statement anyway.
First of all, if/else doesn't require continue. It's optional.
From what I understand you want to know why you used continue in the first if/else and not in the last if/else.
In the first one, after executing if statement it will transfer the control to while True: but for the last if/else statement it is not needed as the control will automatically go to while True: as it is the end of the loop and even if you had used continue it wouldn't have made a difference.
For further references
If you want to know why the continue is not always in if or else, this is due to the fact that when the operation arrives (true), the loop is exited and the code continues to run.
I am relatively new to python, and have been working on a problem to find the prime numbers between two inputs. I have a solution that works (helped somewhat by online searching too), but am unsure on why the else statement shown below should not be at the same tab setting as the if statement. If it is, though, it doesn't work correctly. Can anyone clarify this for me?
My code is here:
n1 = int(input("Enter the lower number: "))
n2 = int(input("Enter the higher number: "))
for num in range(n1, n2 + 1):
if num > 1:
for i in range(2, num):
if num % i == 0:
break
else:
print(num)
You're seeing Python's (rather unique) for:else: pattern, to execute something when a break is not encountered within the for suite:
When the items are exhausted, the suite in the else clause, if present, is executed, and the loop terminates.
A break statement executed in the first suite terminates the loop without executing the else clause’s suite. [...]
this is code to print the lowest positive integer present in a list.
break statement is not working and the loop is running infinitely.
list = []
n=1
print("enter array")
for i in range (5) :
a=(int(input()))
list.append(a)
while n<4 :
for i in range (5) :
if(list[i]== n):
n=n+1
continue
else:
print("the number should be" , n)
break
the break statement refers to the inner most loop level
the code below is an infinite loop:
while True:
for i in range(10):
if i == 5:
break # breaks the for, start a new iteration of the while loop
To break the while loop, you may consider using some kind of flag like this
while True:
broken = False
for i in xrange(10):
if i == 5:
broken = True
# break the for loop
break
if broken:
# break the while loop
break
the for-else statement may also be helpful here:
while True:
for ...:
if ...:
# break the for loop
break # refers to the for statement
else:
# the breaking condition was never met during the for loop
continue # refers to the while statement
# this part only execute if the for loop was broken
break # refers to the while statement
I have previously studied Visual Basic for Applications and am slowly getting up to speed with python this week. As I am a new programmer, please bear with me. I understand most of the concepts so far that I've encountered but currently am at a brick wall.
I've written a few functions to help me code a number guessing game. The user enters a 4 digit number. If it matches the programs generated one (I've coded this already) a Y is appended to the output list. If not, an N.
EG. I enter 4567, number is 4568. Output printed from the list is YYYN.
import random
def A():
digit = random.randint(0, 9)
return digit
def B():
numList = list()
for counter in range(0,4):
numList.append(A())
return numList
def X():
output = []
number = input("Please enter the first 4 digit number: ")
number2= B()
for i in range(0, len(number)):
if number[i] == number2[i]:
results.append("Y")
else:
results.append("N")
print(output)
X()
I've coded all this however theres a few things it lacks:
A loop. I don't know how I can loop it so I can get it to ask again. I only want the person to be able to guess 5 times. I'm imagining some sort of for loop with a counter like "From counter 1-5, when I reach 5 I end" but uncertain how to program this.
I've coded a standalone validation code snippet but don't know how I could integrate this in the loop, so for instance if someone entered 444a it should say that this is not a valid entry and let them try again. I made an attempt at this below.
while myNumber.isnumeric() == True and len(myNumber) == 4:
for i in range(0, 4)):
if myNumber[i] == progsNumber[i]:
outputList.append("Y")
else:
outputList.append("N")
Made some good attempts at trying to work this out but struggling to patch it all together. Is anyone able to show me some direction into getting this all together to form a working program? I hope these core elements that I've coded might help you help me!
To answer both your questions:
Loops, luckily, are easy. To loop over some code five times you can set tries = 5, then do while tries > 0: and somewhere inside the loop do a tries -= 1.
If you want to get out of the loop ahead of time (when the user answered correctly), you can simply use the break keyword to "break" out of the loop. You could also, if you'd prefer, set tries = 0 so loop doesn't continue iterating.
You'd probably want to put your validation inside the loop in an if (with the same statements as the while loop you tried). Only check if the input is valid and otherwise continue to stop with the current iteration of your loop and continue on to the next one (restart the while).
So in code:
answer = [random.randint(0, 9) for i in range(4)]
tries = 5
while tries > 0:
number = input("Please enter the first 4 digit number: ")
if not number.isnumeric() or not len(number) == len(answer):
print('Invalid input!')
continue
out = ''
for i in range(len(answer)):
out += 'Y' if int(number[i]) == answer[i] else 'N'
if out == 'Y' * len(answer):
print('Good job!')
break
tries -= 1
print(out)
else:
print('Aww, you failed')
I also added an else after the while for when tries reaches zero to catch a failure (see the Python docs or maybe this SO answer)
I'm having some trouble with breaking out of these loops:
done = False
while not done:
while True:
print("Hello driver. You are travelling at 100km/h. Please enter the current time:")
starttime = input("")
try:
stime = int(starttime)
break
except ValueError:
print("Please enter a number!")
x = len(starttime)
while True:
if x < 4:
print("Your input time is smaller than 4-digits. Please enter a proper time.")
break
if x > 4:
print("Your input time is greater than 4-digits. Please enter a proper time.")
break
else:
break
It recognizes whether the number is < 4 or > 4 but even when the number inputted is 4-digits long it returns to the start of the program rather than continues to the next segment of code, which isn't here.
You obviously want to use the variable done as a flag. So you have to set it just before your last break (when you are done).
...
else:
done = 1
break
The reason it "returns to the beginning of the program" is because you've nested while loops inside a while loop. The break statement is very simple: it ends the (for or while) loop the program is currently executing. This has no bearing on anything outside the scope of that specific loop. Calling break inside your nested loop will inevitably end up at the same point.
If what you want is to end all execution within any particular block of code, regardless of how deeply you're nested (and what you're encountering is a symptom of the issues with deeply-nested code), you should move that code into a separate function. At that point you can use return to end the entire method.
Here's an example:
def breakNestedWhile():
while (True):
while (True):
print("This only prints once.")
return
All of this is secondary to the fact that there's no real reason for you to be doing things the way you are above - it's almost never a good idea to nest while loops, you have two while loops with the same condition, which seems pointless, and you've got a boolean flag, done, which you never bother to use. If you'd actually set done to True in your nested whiles, the parent while loop won't execute after you break.
input() can take an optional prompt string. I've tried to clean up the flow a bit here, I hope it's helpful as a reference.
x = 0
print("Hello driver. You are travelling at 100km/h.")
while x != 4:
starttime = input("Please enter the current time: ")
try:
stime = int(starttime)
x = len(starttime)
if x != 4:
print("You input ({}) digits, 4-digits are required. Please enter a proper time.".format(x))
except ValueError:
print("Please enter a number!")