Let's say you're asked for input, such as your age, but instead of putting your age in, you accidentally hit 'enter.' The program, however, ignores the keystroke and goes to the next step. Your age is not entered but is regarded as empty/null value.
How do you code to fix this problem?
Thank you
With a while loop, you do not need to write the input() function twice:
while True:
age = input('>> Age: ')
if age:
break
print('Please enter your age')
You might also check if the input is an integer and get an integer from the string. An empty string for age will also raise a ValueError exception:
while True:
try:
age = int(input('>> Age: '))
except ValueError:
print('Incorrect input')
continue
else:
break
age = raw_input("Age: ")
while not age: # In Python, empty strings meet this condition. So does [] and {}. :)
print "Error!"
age = raw_input("Age: ")
You can create a wrapper function for this.
def not_empty_input(prompt):
input = raw_input(prompt)
while not input: # In Python, empty strings meet this condition. So does [] and {}. :)
print "Error! No input specified."
input = raw_input(prompt)
return input
Then:
address = not_empty_input("Address: ")
age = not_empty_input("Age: ")
Related
here is my code
name = input("Enter your name:")
print("Hello, " +name)
age = input("Please enter your age:")
# do exception handling to make sure age is in integer format
age = int(age)
if age >18:
print("welcome")
#here i want to add my password number + strings
password = input("type your code now")
password = int(password)
if password==1234xyz:
print("okay")
else :
print("wrong")
if age < 18:
print("chole jao")
i want to add passwor liek 12323rtrt
You could do the error handling like follows -
name = input("Enter your name:")
print("Hello, " +name)
age = input("Please enter your age:")
# do exception handling to make sure age is in integer format
if age.isdigit() == True:
age = int(age)
if age >18:
print("welcome")
else :
print('age should be a positive integer')
In the second case, you need to know that you cannot convert a string which as alphabets into an integer. So int(password) won't work if the password has some characters. Also, you don't really need to convert the password to an integer. You can directly check/compare the user-inputted password against correct password as follows -
password = input("type your code now")
if password=='1234xyz': # note '1234xyz' which is string can directly be used and this is correct way
print("okay")
else :
print("wrong")
I have a problem in which users can input spaces or nothing and still pass through the program, how do I go about preventing this? I am still a beginner at python.
def orderFunction(): # The function which allows the customer to choose delivery or pickup
global deliveryPickup
deliveryPickup = input("Please input delivery or pickup: d for delivery p for pickup")
if deliveryPickup == "d":
global customerName
while True:
try:
customerName = (input("Please input your name"))
if customerName == (""):
print("Please input a valid name")
else:
break
global customerAddress
while True:
try:
customerAddress = (input("Please input your name"))
if customerAddress == (""):
print("Please input a valid Address")
else:
break
global customerPhnum
while True:
try:
customerPhnum = int(input("Please input your phone number"))
except ValueError:
print("Please input a valid phone number")
else:
break
print("There will also be a $3 delivery surcharge")
elif deliveryPickup == "p":
customerName = (input("Please input your name"))
if customerName == (""):
print("Please input a valid name")
orderFunction()
else:
print("Please ensure that you have chosen d for Delivery or p for Pickup")
orderFunction()
orderFunction()
Here is my attempt at doing this but I get all kinds of unindent and indent errors at the moment and I think my while loops are probably wrong.
Essentially if I input a space or hit enter into one of the customer inputs (customerName for instance) it gets stored. This needs to prevented and I have tried to fix it by using while loops which obviously haven't worked.
Hopefully someone has a solution to this problem
Many Thanks.
.strip() removes all tabs or spaces before and after a string.
Meaning all spaces == empty string. All tabs == empty string. So all you have to check if the length of that string != 0 or the string is not empty. Just use an infinite loop to keep on forcing the right input.
Also as a tip, you don't have to limit yourself into one function.
Here's a working code below.
def getNonBlankInput(message, error_message):
x = input(message)
while len(x.strip()) == 0:
x = input(error_message)
return x
def getValidIntegerInput(message, error_message):
msg = message
while(True):
try:
x = int(input(msg))
break
except ValueError:
msg = error_message
return x
def orderFunction(): # The function which allows the customer to choose delivery or pickup
global deliveryPickup
global customerName
global customerAddress
global customerPhnum
deliveryPickup = input("Please input delivery or pickup: d for delivery p for pickup")
if deliveryPickup == "d":
customerName = getNonBlankInput("Please input your name: ", "Please input a valid name: ")
customerAddress = getNonBlankInput("Please input your address: ", "Please input a valid address: ")
customerPhnum = getValidIntegerInput("Please input your phone number: ", "Please input a valid phone number: ")
print("There will also be a $3 delivery surcharge")
elif deliveryPickup == "p":
customerName = getNonBlankInput("Please input your name: ", "Please input a valid name: ")
else:
print("Please ensure that you have chosen d for Delivery or p for Pickup")
orderFunction()
orderFunction()
Try using a regular expression that checks if any character between "A-Z" has been inserted, if not, give an error
The while loops are a decent solution, you just need to add more checks to your if statements.
First, you don't need a try statement on the top two loops. Don't use a try statement unless you're expecting an error, which you need to handle with an except statement, like you do in the bottom while loop.
Then you just need to add more conditions to your top two loops, I don't know exactly what you want to prevent, but you could try checking the length of the input, also see this answer for an interesting method:
https://stackoverflow.com/a/2405300/8201979
Instead of using input right away you can make a function similar to this one that will only allow valid inputs.
You can use this valid_input function instead of input.
def valid_input(text):
not_valid = True
res = ''
while not_valid:
res = input(text)
if res.split(): # if text is empty or only spaces, this creates an empty list evaluated at False
not_valid = False
return res
here the check is pretty simple: every text made out of nothing or spaces won't be allowed and we will keep asking for the same input until a valid information is given.
I made this code simple just so you get a general idea. But you can change the validation test to your liking and maybe also output a warning saying why the input wasn't allowed so the person knows what to do. You can do more advanced validation with regex, and maybe you need a minimum text length etc...
You have indent error because you have a try statement without the corresponding except.
You need both to make it work (as you did in the Phone number section).
Here is a link to the try/except: docs
Also, you can check if a string is empty as detailed in this answer.
So for example you want to write:
try:
customerName = input("Please input your name")
if not customerName:
print("Please input a valid name")
else:
break
except ValueError:
print("Please input a valid name")
Although the above seems a bit redundant, so you might want to raise an exception if the customer name is empty, catch the exception in the except block, print the warning and return error (or something else).
try:
customerName = input("Please input your name")
if not customerName:
raise ValueError
except ValueError:
print("Please input a valid name")
else:
break
Try adding another while true for pick and delivery option so that it can prevent taking other inputs
you don't need any of those try/excepts (which are broken anyway).
Its difficult to figure out what you're trying to do, are you trying to raise an exception if an empty string is passed, or request another input from the user? You seem to be half implementing both at the moment.
If its the latter, something like this would work.
def func(fieldname):
while True:
val = input("Please input your {}".format(fieldname))
if val.strip() != "":
break
else:
print("Please input a valid {}".format(fieldname))
return val
delivery_pickup = input("Please input delivery or pickup: d for delivery p for pickup")
if delivery_pickup == "d":
customer_name = func("name")
address = func("address")
phone_number = func("phone number")
What you are looking for is the str.strip method that remove trailing whitespace in strings.
Also I think try is not particularly suited for your needs here.
customerName = input("Please input your name")
while not customerName.strip():
customerName = input("Please input a valid name")
for the phone number I would not convert to integer because if the phone number starts with zeros, they will not be stored.
So I have for example the following while statements and I would like to combine them. Because this can get tiresome if you have 20 of these with all different if statements.
while True:
name = str(raw_input("NAME PLEASE\n"))
if name.isalpha():
break
print("Please chars dude")
while True:
age = raw_input("Please type your age\n")
if age.isdigit():
break
print("Please digits only")
If I combine them and someone types a A-Z character with 'age' then the code restarts all over without having saved the 'name' statement. I would like it to save 'name' if it's correct and only start over from the if statement that was false.
while True:
name = str(raw_input("NAME PLEASE\n"))
if name.isalpha():
break
print("Please chars dude")
age = raw_input("Please type your age\n")
if age.isdigit():
break
print("Please digits only")
Use a function to encapsulate asking for information. You can pass in a validation test function:
def ask(question, validator, errormessage):
while True:
result = raw_input(question)
if not validator(result):
print(errormessage)
continue
return result
name = ask("NAME PLEASE\n", lambda s: s.isalpha(), "Please chars dude")
age = ask("Please type your age\n", lambda s: s.isdigit(), "Please digits only")
This is far more readable then any number of tests to see if the user already entered a correct name and you only need to ask for the age now.
Why not use functions and cut down on some duplication in the process?
def ask_input(prompt, error_msg, validation_fn):
while True:
data = raw_input(prompt)
if validation_fn(data):
return data
print(error_msg)
name = ask_input("NAME PLEASE\n", "Please chars dude", lambda x: x.isalpha())
age = ask_input("Please type your age\n", "Please digits only",
lambda x: x.isdigit())
In this case, the prompt (what to ask the user), an error message (what to provide on invalid input), and a validation function are provided to the ask_input() function. This hides the while loop behind the function call and gives you something more meaningful to read in the code.
The lambda functions are just an easy way to help do the validation. You could do this instead:
def isalpha(x):
return x.isalpha()
def isdigit(x):
return x.isdigit()
name = ask_input("NAME PLEASE\n", "Please chars dude", isalpha)
age = ask_input("Please type your age\n", "Please digits only", isdigit)
You can set the variables to None first, and then check them before assignment:
name, age = None, None
while True:
if name is None:
name = str(raw_input("NAME PLEASE\n"))
if not name.isalpha():
print("Please chars dude")
name = None
continue
if age is None:
age = raw_input("Please type your age\n")
if not age.isdigit():
print("Please digits only")
age = None
continue
print("input is valid")
break
continue will start the loop over again. This fits better in the logic of your code, since break actually stop and exit the loop code.
Just use flags to track weather valid input is given, if given then exit the loop.
name_input_required = True
name = ''
while name_input_required:
name = str(raw_input("NAME PLEASE\n"))
if name.isalpha():
name_input_required = False
else:
print("Please chars dude")
age_input_required = True
age = None
while age_input_required:
age = raw_input("Please type your age\n")
if age.isdigit():
age_input_required = False
else:
print("Please digits only")
Try this:
name = None
age = None
while requires_info:
if name is None:
temp_name = str(raw_input("NAME PLEASE\n"))
if temp_name.isalpha():
name = temp_name
continue
else:
print("Please chars dude")
continue
if age is None:
temp_age = raw_input("Please type your age\n")
if temp_age.isdigit():
age = temp_age
continue
else:
print("Please digits only")
continue
break
What we do here is use a single continuous loop and a few if statements/variables to track what still needs to be done. Note depending on how you want them to enter the data you may also add logic to not ask for age if the name was invalid.
So I have for example the following while statements and I would like to combine them. Because this can get tiresome if you have 20 of these with all different if statements.
I assume the actual problem is "How to reduce tiresome code?" instead of "How to merge two loops into one?". I think keeping two loops is a good idea.
def safe_input(prompt, err_message, validation_fn):
while True:
value = raw_input(prompt)
if validation_fn(value):
return value
print err_message
name = safe_input("NAME PLEASE\n", "Please chars dude", str.isalpha)
age = safe_input("Please type your age\n", "Please digits only", str.isdigit)
If you always want the used to enter text in a separate line, you might want to print prompt before raw_input and to not give an argument to raw_input. That way you don't have to supply "\n" in every call of safe_input.
Yes, you can combine both loops in one loop!
Always try to solve the problem line by line.
You will get to learn the language better and it is the most simple way to solve any problem too.
A line by line solution would look like this:
name = '' # define name outside while loop
while True:
if not name:
name = str(raw_input("NAME PLEASE\n"))
if not name.isalpha(): # validate name
print("Please chars dude")
# reset name
name = ''
else:
age = raw_input("Please type your age\n")
if age.isdigit(): # validate age
"""continue your code here"""
print('name: ' + name + ' and age: ' + age)
print('Ok! Goodbye!')
break # while loop
else:
print("Please digits only")
will print:
NAME PLEASE
Elis
Please type your age
30
name: Elis and age: 30
Ok! Goodbye!
This will help you understand while loop better and how to use it in more difficult cases.
Do not over design using redundant language features. It will make refactoring and debugging difficult.
When I was developing my first code I faced a problem which with the break command which I tried to use to restart the program if there's an error.
Take a look on the code maybe you would understand better.
Name = str(input("Please enter Your Name:"))
Age = input("Please enter your age: ")
if Age != int():
print ("Error! Check the age")
break
elif Age == int():
continue
Height = input("Please enter your height: ")
if Height != int():
print ("Error! Check the Height")
break
elif Height == int():
continue
if Age == int() and Age >= 18 and Height == int() and Height >= 148:
print("You're able to drive a car " + (Name) )
elif Age == int() and Age < 18 and Height == int() and Height > 148:
print("You're not able to drive a car " + (Name) )
elif Age and Height != int() :
print ("Error! , Age or Height are not numbers")
error:
"C:\Users\Ghanim\Desktop\Coding\Documents\Projects\Python\Project1\Project1.py", line 6
break
^
SyntaxError: 'break'
outside loop
The break statement is used to exit loops, not the program. Use sys.exit() to quit the program, you'll need to import sys too.
EDIT:
In answer to your comment, this is how I'd probably do it:
while True:
inputted_name = input("Please enter your name:")
try:
name = str(inputted_name)
except ValueError:
print("Please enter a valid name")
else:
break
while True:
inputted_age = input("Please enter your age:")
try:
age = int(inputted_age)
except ValueError:
print("Please enter a valid age")
else:
break
while True:
inputted_height = input("Please enter your height:")
try:
height = float(inputted_height)
except ValueError:
print("Please enter a valid height")
else:
break
if age >= 18 and height >= 148:
print("You're able to drive a car {}".format(inputted_name))
if age < 18 and height > 148:
print("You're not able to drive a car {}".format(inputted_name))
So there are a few changes:
Each stage of the user input is in its own loop. I've used try/except/else statements which try to cast the input to the correct type, except ValueErrors (thrown if it cant be cast, which will happen if the user puts a text answer to the input age for example. If it casts to the correct type successfully, the loop is broken and the script moves onto the next one. Having separate loops for each one means if the user puts in an incorrect value for one of them, they don't have to redo the whole thing.
I've also used format() to insert name into the final strings to avoid having to do string concatenation.
Also, just a quick note, I'm assuming you're using Python 3 for this. However, if you're using Python 2 input() should be replaced with raw_input(). In Python 2 input() will try and evaluate the user input as an expression, whereas raw_input() will return a string.
The break statement breaks out of a loop (for-loop or while-loop). Outside of this context it does not make sense.
break cannot restart your program, break can only be used in loop such as for or while.
In you case, just use exit(-1)
there is no loop in your program. break can't be used outside a loop. You can use sys.exit() instead of breakand pass instead of continue.
I have a program that asks the user's name:
while True:
try:
name = str(input("Please enter your name > "))
except ValueError:
print("Please enter a valid name")
continue
else:
break
I want to prevent the user from entering an integer, but with the code above integers are accepted in a string. How can I prevent the user from entering an integer in the string?
Firstly, do not cast str as input returns an str. Note from the docs
The function then reads a line from input, converts it to a string (stripping a trailing newline), and returns that
After you get the input into name you can have a if condition.
name = str(input("Please enter your name > "))
if (re.search('\d',name)):
print("Sorry your name contains a number")
And don't forget to import re
break when trying to cast to an int if an exception is raised as it is not an int:
while True:
name = input("Please enter your name > ")
try:
int(name)
except ValueError:
break
print("Please enter a valid name")
str.digit might work also but will fail on negative input.
To check if any character is a digit use any:
while True:
name = input("Please enter your name > ")
if any(ch.isdigit() for ch in name):
print("Please enter a valid name")
else:
break
You could also create a set of accepted characters:
from string import ascii_letters
st = set(ascii_letters)
while True:
name = input("Please enter your name > ")
if not st.issuperset(name):
print("Please enter a valid name")
else:
break
Where you might want to add -, " " and any other potential characters.
You can use the string method isdigit() to check if the string is just integers.
name = input("Please enter your name: ")
if name.isdigit() == True:
print ("That's not a name!")
Likewise, you can also use the method isalpha() to check if the string is just text. However, if there's a space, it will return False.
name = input("Enter your name: ")
if name.isalpha() != True:
print ("That's not a name!")
Maybe:
if len(set(name) - set('1234567890')) < len(set(name)):
name = input("Please enter a valid name: ")