I can't seem to be able to get the correct total number of attempts to be displayed.
def checkAge():
Age=int(input("EnterAge:"))
attempts=0
if Age>=100:
attempts=attempts+1;
return checkAge()
elif Age<=1:
attempts=attempts+1;
return checkAge()
else:
attempts=attempts+1;
print("Your age is",Age,".")
print("Number of attempts: ",attempts,"")
Typing in 234 then 432 then 52, I expect the result for the attempts to be:
"Number of attempts:3"
but it shows me:
"Number of attempts:1"
attempts is being reset to 0 on each function call. You should create a parameter that you pass to checkAge and remove the variable instantiation attempts=0.
An updated function might look like
def checkAge(attempts):
Age=int(input("EnterAge:"))
if Age>=100:
attempts=attempts+1;
return checkAge(attempts)
elif Age<=1:
attempts=attempts+1;
return checkAge(attempts)
else:
attempts=attempts+1;
print("Your age is",Age,".")
print("Number of attempts: ",attempts,"")
Your problem arises mainly because you try to call your function recursively when it fails, which is a bad idea, because:
there is a limit to the number of recursive calls you can make (by default, 1000 with the common implementation of Python)
as you would have to do here, you have to pass variables between calls of the function.
the order of execution can become complicated to follow because of the imbricated calls / returns
The right way to do what you want here it is to use a loop:
def checkAge():
attempts = 0
while True:
attempts += 1
try:
age = int(input("Enter Age: "))
except ValueError:
# what we entered couldn't be converted to an integer
continue
if 1 < age <100:
return age, attempts
age, attempts = checkAge()
print("Your age is {}.".format(age))
print("Number of attempts: ", attempts, "")
Sample run:
# Enter Age: abc
# Enter Age: 122
# Enter Age: 0
# Enter Age: 33
# Your age is 33.
# Number of attempts: 4
I added a try/except block around the call to int(input(...)), as this would raise an exception and crash your program otherwise if the user didn't enter a valid number.
Also, it is better for functions to return data rather than print it directly, that makes them more versatile - you can decide what you do with the returned data.
Using format gives you more control on the printed output (here, it allows you to have the final dot just after the number, instead of separated by an extra space).
Every time you run your method checkAge() attempts is assigned the value of 0 so no matter how often you run it, it will always do: attempts = 0 then attempts = 0 + 1
You need to initialize your variable outside of your method, check if it already exists (only assign 0 if attempts is null) or implement it in a different way so it won't reset to 0 every time.
Related
I have created a simple program which asks for a user's name and age. The program will then take the details from a textbox and work out how old they will be in 5 years time.
The interface is fine. It's the validation that I am having difficulty with. When a user enters a letter instead of a number the program shows an error message, but continues to run regardless. I have tried using a while True: loop but this seems to just crash the program.
Here's what I have written already:
def calculate():
name = (textboxName.get())
age = (textboxAge.get())
if age.isalpha():
tkinter.messagebox.showinfo("Error", "The Age is invalid")
textboxAge.delete("0","end")
newAge = int(age)+5
print("Hello",name)
print("In 5 years time you will be",newAge)
I have looked at a few other tutorials but they are a little confusing. I am going to extend this by adding another elif in and the following code
elif age >= 100:
tkinter.messagebox.showinfo("Error", "You have entered a number greater than 100")
textboxAge.delete("0","end")
but this doesn't like the fact it is a string not an integer.
What would be the best way to check to see if a number has been entered into a textbox?
def calculate():
name = (textboxName.get())
age = (textboxAge.get())
try:
newAge = int(age)+5
except ValueError:
tkinter.messagebox.showinfo("Error", "The Intended Reading Age is invalid")
textboxAge.delete("0","end")
return
print("Hello",name)
print("In 5 years time you will be ",newAge)
# ...
If an error occurs somewhere in the try-section, python will not crash, but rather jump to the except part. The critical step is converting age into integer. This throws a ValueError if it is a string. In this case, the message box is shown and the text in your textbox is deleted. return then will stop the function, so the rest of it won't be processed. If nothing happens in the try-section, then except will be skipped.
I am new to python and came around a scenario explained below-:
This is one from the .pdf I am referring to learn. Would be great if anyone could guide or share some other resources.
A program which repeatedly reads numbers until the user enters “done”. Once “done” is entered, print out the total, count, and average of the numbers. If the user enters anything other than a number, detect their mistake using try and except and print an error message and skip to the next number.
Enter a number: 4
Enter a number: 5
Enter a number: bad data
Invalid input
Enter a number: 7
Enter a number: done
16 3 5.333333333333333*
I am unable to store the values into list.
Tried going with this logic-:
while True:
line = input('Enter Number-: ')
if type(line) == int():
continue
if line == 'done':
break
print(line)
print('Done!')
Just need to know how to store into lists without using spaces or commas,
The user should be able to enter the value as shown in example above and those should get stored in a list.
Thanks in advance.
In Python 2.7, input will evalulate any entry and will fail if the input is not a correct Python type to begin with. It's better to use raw_input here as any entry will be considered a string. If you move to Python 3, raw_input was removed and input acts how raw_input did. So your example expects you to give it '45' or 'done' instead of 45 or done.
But the reason you're unable to store any values into a list is because you're not adding them to a list in the first place. But since we've also switched to raw_input, we don't know if the entry is a valid number or not. So we need to try to convert it to a number and if it isn't one, then check to see if it's the keyword telling the code to stop.
values = [] # make an empty list
while True:
line = raw_input('Enter Number-: ') # all entries here are considered strings
try:
num = int(line) # convert to an integer
values.append(num) # add to list
continue # return to input query
except: # int(line) threw an error, so not a valid number input
if line == 'done': # check if should stop
break # get out of loop
else: # anything else
print 'bad data, invalid input'
continue # return to input query
print 'Done!\n'
print 'total:', sum(values)
print 'count:', len(values)
print 'average:', sum(values) / float(len(values))
If you're entering more than just integers, you may wish to change num = int(line) to num = float(line) to handle decimal inputs, as int only accepts integers.
Enter Number-: 4
Enter Number-: 5
Enter Number-:
bad data, invalid input
Enter Number-: 7
Enter Number-: done
Done!
total: 16
count: 3
average: 5.33333333333
The Tutorial may also be helpful in learning Python.
I have this function below, which I have done something wrong in somewhere.
def quantityFunction(product):
valid = False
while True:
if product is not None:
quantity = input("Please enter the amount of this item you would like to purchase: ")
for i in quantity:
try:
int(i)
return int(quantity)
valid = True
except ValueError:
print("We didn't recognise that number. Please try again.")
#If I get here, I want to loop back to the start of this function
return True
return False
To run through, the function is called from the main part of the program like so: quantity = quantityFunction(product)
The return False at the bottom of the code is to do with if product is None, which is needed after a bit of code in another function but has had to go in this function.
If the user input for quantity is a number, all works fine. If it is anything else, the Value Error is printed and you can enter another input. If you put another letter etc in, it repeats again, if you put a number in, it accepts it.
However, it does not return the number you inputted after the letters. It just returns 0.
I suspect this is something to do with how I am repeating the code, i.e. the code should loop back to the start of the function if it hits the Value Error.
Any Ideas?
You said:
the code should loop back to the start of the function if it hits the Value Error.
Then you should not use return statements, otherwise the function will terminate, returning True or False.
Few issue:
1) return statement returns control to the calling function.
2) You are looping over the input, which is wrong.
3) valid=True isn't executed at all.
def quantityFunction(product):
valid = False
while True:
if product is not None:
quantity = raw_input("Please enter the amount of this item you would like to purchase: ")
try:
return int(quantity)
#valid = True (since it is never run)
except ValueError:
print("We didn't recognise that number. Please try again.")
#If I get here, I want to loop back to the start of this function
#return True
return False
quantityFunction("val")
Note : Use raw_input() in case of Python 2.7 and input() in case of 3.x
Try this (some formatting included too, but the functionality should be the same):
def determine_quantity(product): # descriptive function name
if not product: # avoiding nesting
return False
while True:
quantity = input("Please enter the amount of this item you would like to purchase: ")
try:
return int(quantity) # try to convert quantity straight away
except ValueError:
print("We didn't recognise that number. Please try again.")
# nothing here means we simply continue in the while loop
Ideally, you'd take product out. A function should do as little as possible, and this check is better off somewhere else.
def determine_quantity():
while True:
quantity = input("Please enter the amount of this item you would like to purchase: ")
try:
return int(quantity)
except ValueError:
print("We didn't recognise that number. Please try again.")
First, let's address the code. Simply stated, you want a function that will loop until the user enters a legal quantity.
product doesn't do much for the function; check it in the calling program, not here. Let the function have a single purpose: fetch a valid quantity.
Let's work from there in the standard recipe for "loop until good input". Very simply, it looks like:
Get first input
Until input is valid
... print warning message and get a new value.
In code, it looks like this.
def get_quantity():
quantity_str = input("Please enter the amount of this item you would like to purchase: ")
while not quantity_str.isdigit():
print("We didn't recognise that number. Please try again.")
quantity_str = input("Please enter the amount of this item you would like to purchase: ")
return quantity
As for coding practice ...
Develop incrementally: write a few lines of code to add one feature to what you have. Debug that. Get it working before you add more.
Learn your language features. In the code you've posted, you misuse for, in, return, and a function call.
Look up how to solve simple problems. try/except is a more difficult concept to handle than the simple isdigit.
You should try this..
def quantityFunction(product):
valid = False
while True:
if product is not None:
quantity = raw_input("Please enter the amount of this item you would like to purchase: ")
if quantity.isdigit():
return int(quantity)
valid = True
else:
print("We didn't recognise that number. Please try again.")
continue
return False
quantity = quantityFunction("myproduct")
I am very new to Python (started 2 days ago). I was trying to validate positive integers. The code does validate the numbers but it asks twice after a wrong input is entered. For example if I enter the word Python, it says: This is not an integer! like is supposed to but if I enter 20 afterwards, it also says it is not an integer and if I enter 20 again it reads it.
def is_positive_integer(input):
#error: when a non-integer is input and then an integer is input it takes two tries to read the integer
flag = 0
while flag != 1:
try:
input = int(input)
if input <= 0:
print "This is not a positive integer!"
input = raw_input("Enter the number again:")
except ValueError:
print "This is not an integer!"
input = raw_input("Enter the number again: ")
if isinstance(input, int):
flag = 1
return input
number = raw_input("Enter the number to be expanded: ")
is_positive_integer(number)
number = int(is_positive_integer(number))
Any help is appreciated.
The main bug is that you call is_positive_integer(number) twice with the same input (the first thing you enter).
The first time you call is_positive_integer(number), you throw away the return value. Only the second time do you assign the result to number.
You can "fix" your program by removing the line with just is_positive_integer(number) on its own.
However, your code is a little messy, and the name is_positive_integer does not describe what the function actually does.
I would refactor a little like this:
def input_positive_integer(prompt):
input = raw_input(prompt)
while True:
try:
input = int(input)
if input <= 0:
print "This is not a positive integer!"
else:
return input
except ValueError:
print "This is not an integer!"
input = raw_input("Enter the number again: ")
number = input_positive_integer("Enter the number to be expanded: ")
The problem stems from the fact that you're calling is_positive_integer twice. So, the first time it's called, you send it a string like 'hello', then it says it's not an integer and tells you to try again. Then you enter '20', which parses fine, and it's returned.
But then you don't save a reference to that, so it goes nowhere.
Then you call the function again, this time saving a reference to it, and it first tries the original bad string, which was still there in number. Then it complains that it's a bad input, asks you for a new one, and you provide it, terminating the program.
Question: What would be the issue if python continues to ask for the same input over and over again, and won't advance to the end of the program?
Where do you want to go? X
And how many days will you be staying in X? 1
And how many days will you be staying in X? 2
And how many days will you be staying in X? 164
And how many days will you be staying in X? 59
...
Here's the relevant part of the code:
# Import modules
import destinations
import currency
save_itinerary = True
main_function = True
while (main_function):
# Determine length of stay
while True:
try:
length_of_stay = int(input("And how many days will you be staying in " + destinations.destination[0] + "? "))
# Check for non-positive input
if (length_of_stay <= 0):
print("Please enter a positive number of days.")
continue
except ValueError:
print("The value you entered is invalid. Only numerical values are valid.")
break
else:
break
The reason your code is looping forever is that you have two nested while loops, and you never break out of the outer one. You do use break statements to exit the inner loop, but the condition for the outer loop is never changed, and you never execute a break at the right level to exit it.
Here's what I think a better version of your code would be:
# get rid of the outer while loop, which was never ending
while True:
try:
length_of_stay = int(input("And how many days will you be staying in " + destinations.destination[0] + "? "))
if (length_of_stay <= 0):
print("Please enter a positive number of days.")
continue
except ValueError:
print("The value you entered is invalid. Only numerical values are valid.")
# don't break here, you want to stay in the loop!
else:
break
I've used comments to indicate my changes.
You could also move the else: break block up and indent it so that it is attached to the if statement, rather than the try/except statements (and then get rid of the unnecessary continue statement). That's makes the flow a bit more obvious, though there's not really anything wrong with how it is now.