Checking for integers in a string - python - python

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: ")

Related

In my code i want to add my password number + strings , for example 1234xyz

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")

Combine multiple while statements python

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.

Error catching integers in a string

strFName = ""
while strFName != strFName.isalpha():
if strFName != strFName.isalpha():
strFName = input("What is your first name? ")
else:
print("Your name cannot contain numbers")
break
I want the user to enter their name, but if they enter any letters the program will throw up an error. So far I am trying to do this with a try and except but whenever I enter a number it just goes straight on to the next part of the program.

You mean the first name cannot contain digits?
If so, you can do something like this:
import string
has_digits = lambda x: any([i.isdigit() for i in x])
first_name = "0"
while has_digits(first_name):
first_name = input("Enter first name (cannot contain digits): ")
print('Your name is {}'.format(first_name))

How would I disallow numbers as input?

Alright, so I defined a function where the user can input his/her name. I want to make it so that the user is not allowed to input a number like "69" for his/her name. How would I go about doing this? Here is the code I used:
def name():
while True:
name = input("What is your name? "))
try:
return str(name)
break
except TypeError:
print("Make sure to enter your actual name.")

You can use isalpha() to check name:
Return true if all characters in the string are alphabetic and there
is at least one character, false otherwise.
>>> "69".isalpha()
False
>>> "test".isalpha()
True
Here's your code with modifications:
while True:
name = input("What is your name? ")
if name.isalpha():
break
else:
print("Make sure to enter your actual name.")
continue
Or:
name = input("What is your name? ")
while not name.isalpha():
print("Make sure to enter your actual name.")
name = input("What is your name? ")

You can use str.isdigit() method to check if the string contains just digits:
name = input("What is your name? ")
while name.isdigit():
print("Make sure to enter your actual name.")
name = input("What is your name? ")
Note that this will allow names like - "Rohit1234". If you just want to allow alphabetic characters, then you can use str.isalpha() method instead.

Invert your logic:
while True:
name = ...
try:
int(name)
print "Name can't be a number."
except TypeError:
return str(name)
Mind you, this will accept any input that is not a valid integer, including 123abc or so.

coding error msg for typing 'enter'

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: ")

Categories