I am learning Python this semester and this is my homework.
Can anyone tell me why my code is wrong?
QUESTION:
You want to know your grade in Computer Science, so write a program that continuously takes grades between 0 and 100 to standard input until you input "stop", at which point it should print your average to standard output.
MY CODE:
total=0
count=0
while True:
grade=input("Enter Your Grades between 0 and 100 [put 'stop' when done]:")
if grade<0 or grade>100:
print("Invalid Input")
continue
elif grade=="stop":
break
else:
count+=1
total+=grade
print "Your Average Grade is:"+format(total/count,'.2f')
When I run the code, the Python keeps giving me this messages:
Change input to raw_input
grade = raw_input("Enter Your Grades between 0 and 100 [put 'stop' when done]:")
You are using Python 2.7, so use raw_input instead of input. The latter evaluates the input, so 5 + 2 will return 7 instead of the string '5 + 2'. Entering stop tries to evaluate stop as a variable, which doesn't exist.
Another note, total and count are both integers, so total/count performs integer division in Python 2 (Python 3 gives a float result). If you want a floating point average, use float(total)/count. One of the variables must be float to get a float answer.
You'll also find that grade is a string, so test for 'stop' first, then convert it to an int to test the grade grade = int(grade). You might want to think about handling errors. What if the user types 10a?
You can evaluate first the string stop, try capture the input with raw_input:
total = 0
count = 0
while True:
grade = raw_input("Enter Your Grades between 0 and 100 [put 'stop' when done]:")
if grade == "stop":
break
if grade.isdigit():
grade = int(grade)
if grade < 0 or grade > 100:
print("Invalid Input")
continue
else:
count += 1
total += grade
if count == 0:
print "Empty values"
else:
print "Your Average Grade is: %.2f" % (float(total)/count)
I added different conditions for correct execution, check the lines, for example if grade.isdigit(): for verify that the input value is a numeric value, when this evaluation we can work normally with any math calculation.
count == 0: for the error division by zero if the user write stop in first iteration.
In the last line you can use two different ways to print the values:
print "Your Average Grade is: %.2f" % (float(total)/count)
or
print "Your Average Grade is: {:.2f}".format(float(total)/count)
You're running this program in Python 2 where input evaluates the user input. So if you enter "stop", Python tries to find the variable stop which doesn't exist and raises the NameError.
There are more problems and you need to restructure the code. The first thing you should do is to change input to raw_input which just returns the user input as a string. Then you need to check if the user entered "stop" and break, otherwise convert the input string to an int and then increment the count and total.
total = 0
count = 0
while True:
grade = raw_input("Enter Your Grades between 0 and 100 [put 'stop' when done]:")
if grade == "stop":
break
# Skip if the string can't be converted to an int.
if not grade.isdigit():
print("Invalid Input")
continue
# Now convert the grade to an int.
grade = int(grade)
if grade < 0 or grade > 100:
print("Invalid Input")
continue
else:
count += 1
total += grade
# Convert total to a float for true division.
print "Your Average Grade is: {:.2f}".format(float(total)/count)
Related
What I want to do, is to write a program that given a sequence of real numbers entered by the user, calculates the mean. Entering the sequence should be finished by inputting ’end’. To input more than 1 number I try:
num=input("Enter the number: ")
while num!="end":
num = input("Enter the number: ")
But I don't want the program to "forget" the first 'num', because I'll need to use it later to calculate the mean. What should I write to input and then use more than one value, but not a specific number of values? User should can enter the values until they enter 'end'. All of values need to be use later to calculate the mean. Any tip for me?
First, define an empty list.
numbers = []
Then, ask for your input in an infinite loop. If the input is "end", break out of the loop. If not, append the result of that input() to numbers. Remember to convert it to a float first!
while True:
num = input("Enter a number: ")
if num == "end":
break
numbers.append(float(num))
Finally, calculate the mean:
mean = sum(numbers) / len(numbers)
print("Mean: ", mean)
However, note that calculating the mean only requires that you know the sum of the numbers and the count. If you don't care about remembering all the numbers, you can just keep track of the sum.
total = 0
count = 0
while True:
num = input("Enter a number: ")
if num == "end":
break
total += float(num)
count += 1
print("Mean: ", total / count)
Mean is sum of all nos/total nos. Let's take input from user and add it to list, because we can easily use sum() function to find sum and len() function to find total nos. Your code:
obs=[]
while True:
num=input("Enter number: ")
if num=="end":
break
else:
obs.append(int(num))
print("Mean: ",(sum(obs)/len(obs)))
I'm trying to work out the average of numbers that the user will input. If the user inputs nothing (as in, no value at all) I want to then calculate the average of all numbers that have been input by the user upto that point. Summing those inputs and finding the average is working well, but I'm getting value errors when trying to break the loop when the user inputs nothing. For the if statement I've tried
if number == ''
First attempt that didn't work, also tried if number == int("")
if len(number) == 0
This only works for strings
if Value Error throws up same error
Full code below
sum = 0
while True :
number = int(input('Please enter the number: '))
sum += number
if number == '' :
break
print(sum//number)
Error I'm getting is
number = int(input('Please enter the number: '))
ValueError: invalid literal for int() with base 10:>
Any help much appreciated!
EDIT: Now getting closer thanks to the suggestions in that I can get past the problems of no value input but my calculation of average isn't working out.
Trying this code calculates fine but I'm adding the first input twice before I move to the next input
total = 0
amount = 0
while True :
user_input = input('Please enter the number: ')
try:
number = int(user_input)
total = number + number
amount += 1
except:
break
total += number
print(total/amount)
Now I just want to figure out how I can start the addition from the second input instead of the first.
sum = 0
while True :
number = input('Please enter the number: '))
if number == '' :
break
sum += int(number)
print(sum//number)
try like this
the issue is using int() python try to convert input value to int. So, when its not integer value, python cant convert it. so it raise error. Also you can use Try catch with error and do the break.
You will always get input as a string, and if the input is not a int then you cant convert it to an int. Try:
sum = 0
while True :
number = input('Please enter the number: ')
if number == '' :
break
sum += int(number)
print(sum//number)
All of the answers dont work since the print statement referse to a string.
sum = 0
while True :
user_input = input('Please enter the number: ')
try:
number = int(user_input)
except:
break
sum += number
print(sum//number)
including a user_input will use the last int as devisor.
My answer also makes sure the script does not crash when a string is entered.
The user has to always input something (enter is a character too) for it to end or you will have to give him a time limit.
You can convert character into int after you see it isn't a character or
use try & except.
sum = 0
i = 0
while True :
try:
number = int(input('Please enter the number: '))
except ValueError:
break
i += 1
sum += number
try:
print(sum/number)
except NameError:
print("User didn't input any number")
If you try to convert a character into int it will show ValueError.
So if this Error occurs you can break from the loop.
Also, you are trying to get the average value.
So if a user inputs nothing you get NameError so you can print an Error message.
I am learning Python, and currently I am learning about sentinel loops. I have this piece of code that I need help understanding. What exactly is the while-loop doing? I did some research and I know it is looping through the if-statement (correct me if I am wrong); but is it looping through a specific equation until the user stops inputting their integers? Thank you in advanced.
(Please no hate comments I am still learning as a developer. & this is my first post Thanks)
even = 0 odd = 0
string_value = input("Please enter an int. value: ")
while string_value !="":
int_value = int(string_value)
if int_value % 2 == 0:
even += 1
else:
odd += 1
string_value = input("Please enter an int. value: ")
if even + odd == 0:
print("No values were found. Try again...") else:
print("Number of evens is: ", str(even)+".")
print("Number of odd is: ", str(odd)+".")
---Updated Code:
def main():
print("Process a series of ints enter at console \n")
count_even = 0
count_odd = 0
num_str = input("Please enter an int. value or press <Enter> to stop: ")
#Process with loop
while num_str !="":
num_int = int(num_str)
if num_int % 2 == 0:
count_even += 1
else:
count_odd += 1
num_str = input("Please enter an int. value: ")
if count_even + count_odd == 0:
print("No values were found. Try again...")
else:
print("Number of evens is: ", str(count_even)+".")
print("Number of odd is: ", str(count_odd)+".")
main()
First thing the while loop does is check if the user input is emptywhile string_value !="", if it is not empty than it will start the loop. The != means not equals and the "" is empty so not equals empty. Next it sets the variable int_value as the integer of the user input(will error if user inputs anything other than whole number). Next it checks if the variable int_value % 2(remainder of division by 2) is 0, so pretty much it checks if the number is divisible by 2, if it is divisible by two it will add 1 to the even variable. Otherwise it will add 1 to the odd variable
It will be very helpful if you go through python doc https://docs.python.org/3/tutorial/index.html
even = 0 odd = 0
The above line even and odd are variables keeping count of even number and odd number.
string_value = input("Please enter an int. value: ")
The above line prompt the user to input an integer
while string_value !="":
int_value = int(string_value)
if int_value % 2 == 0:
even += 1
else:
odd += 1
string_value = input("Please enter an int. value: ")
The above while loop check firstly, if the input is not empty, int() Return an integer object constructed from a number or string x, or return 0 if no arguments are given https://docs.python.org/3/library/functions.html#int. The if statement takes the modulus of the integer value, and then increases the counter for either odd or even.
Finally, the count of odd and even are printed.
the input() function waits until the user enters a string so unless the user enters an empty string the while loop will keep asking the user for strings in this line:
string_value = input("Please enter an int. value: ")
and check if its an empty string in this line:
while string_value !="":
I'm trying to create a small code that asks a user to enter a number between 1 and 100. However my Else statement will not output when entering a string. I want my Else statement to print a message if the user enters an input other than an integer or float. Here is my code.
def between():
print ("Please enter a number between 1 and 100.")
number = eval(input())
if number >= 1 and number <= 100:
print ("Thank you! You entered",number,"which is within the 1 and 100 range.")
between()
elif number > 100 or number < 1:
print ("OOPS! You entered",number,"Please enter a number between 1 and 100.")
between()
else:
print ("ERROR! You have entered an invalid value. Please try again using numerical values only.")
between()
between()
The easiest method would be to use try and except
num = input()
try:
number = float(num)
# code to do if num is a number
except ValueError:
print("Not a number!")
# code to do if num isn't a number
If num isn't a number, then converting it to a float would raise ValueError going on to the except.
If num is a number, the coversion of it to a float would run fine, and continue on in the try.
Side note: I highly suggest not using eval(input()) but rather just input(), see this for why you shouldn't use eval. Also eval(input()) won't work with my example above.
Try this:
print "Please enter a number between 1 and 100"
in = input()
try:
num = int(in)
if 1 <= num <= 100:
print("Valid")
else:
print("Out of bounds")
except:
print("Invalid")
Try:
def between():
print ("Please enter a number between 1 and 100.")
number=0
try:
number = int(input())
except:
print ("ERROR! You have entered an invalid value. Please try again using numerical values only.")
exit(1)
if number >= 1 and number <= 100:
print ("Thank you! You entered",number,"which is within the 1 and 100 range.")
between()
else:
print ("OOPS! You entered",number,"Please enter a number between 1 and 100.")
between()
between()
Note: why you use eval and input together? I don't think that's right, correct me if I'm wrong
There are a few logical issues with your code. First before using eval() you must be aware of the security risk associated with it. Consider going through this post for some insight. If you entered some arbitrary input in eval, it will most likely be a run time error.
Now, assuming that the variable actually has a value. To check if it is an integer or a float and is in the desired range or something else (possibly a string), you can not directly apply comparison operators with it because if the variable is not a number it will most likely give a TypeError during comparison with other integers.
Hence a correct approach would be to first check if the variable is of desired type by checking if type(r) is int or type(r) is float only then you should apply test for range. If the above type checking is false then you should print your "else" error message.
Try is too slow and should be avoided when not necessary
num = input("Please enter a number between 1 and 100: ")
if num.replace('.','').isdigit():
num = float(num)
if number >= 1 and number <= 100:
print ("Thank you! You entered",number,"which is within the 1 and 100 range.")
between()
else:
print ("OOPS! You entered",number,"Please enter a number between 1 and 100.")
between()
else:
print('thats not a number!')
I'm currently working on a program in Python and I need to figure out how to convert a string value to a float value.
The program will ask the user to enter a number, and uses a loop to continue asking for more numbers. The user must enter 0 to stop the loop (at which point, the program will give the user the average of all the numbers they entered).
What I want to do is allow the user to enter the word 'stop' instead of 0 to stop the loop. I've tried making a variable for stop = 0, but this causes the program to give me the following error message:
ValueError: could not convert string to float: 'stop'
So how do I make it so that 'stop' can be something the user can enter to stop the loop? Please let me know what I can do to convert the string to float. Thank you so much for your help! :)
Here is some of my code:
count = 0
total = 0
number = float(input("Enter a number (0, or the word 'stop', to stop): "))
while (number != 0):
total += number
count += 1
print("Your average so far is: " , total / count)
number = float(input("Enter a number (0, or the word 'stop', to stop): "))
if (number == 0):
if (count == 0):
print("")
print("Total: 0")
print("Count: 0")
print("Average: 0")
print("")
print("Your average is equal to 0. Cool! ")
else:
print("")
print("Total: " , "%.0f" % total)
print("Count: " , count)
print("Average: " , total / count)
Please let me know what I should do. Thanks.
I'd check the input to see if it equals stop first and if it doesn't I'd try to convert it to float.
if input == "stop":
stop()
else:
value = float(input)
Looking at your code sample I'd do something like this:
userinput = input("Enter a number (0, or the word 'stop', to stop): ")
while (userinput != "stop"):
total += float(userinput) #This is not very faulttolerant.
...
You could tell the user to enter an illegal value - like maybe your program has no use for negative numbers.
Better, would be to test if the string you've just read from sys.stdin.readline() is "stop" before converting to float.
You don't need to convert the string to a float. From what you've said it appears that entering 0 already stops the loop, so all you need to do is edit you're currently existing condition check, replacing 0 with "stop".
Note a few things: if the input is stop it will stop the loop, if it's not a valid number, it will just inform the user that the input were invalid.
while (number != 0):
total += number
count += 1
print("Your average so far is: " , total / count)
user_input = input("Enter a number (0, or the word 'stop', to stop): ")
try:
if str(user_input) == "stop":
number = 0
break
else:
number = float(user_input)
except ValueError:
print("Oops! That was no valid number. Try again...")
PS: note that keeped your code "as is" mostly, but you should be aware to not use explicit counters in python search for enumerate...