CODEWITHSUNDEEP
pythonexception
laxman prasad
laxman prasad

Reputation: 21

Unexpected exception being raised when trying to convert an input string to float

I want to ask the user to input a value and then print its length, if the input is a string. If the user's input is an integer or a decimal, I want to print "Sorry, integers don't have length" or "Sorry, floats don't have length", respectively.

I'm making use of exception while trying to convert the input into float or integer.

Here is my code:

c=input("enter a string: ")

def length(c):
    return len(c)

try:
    float(c)
    if float(c)==int(c):
        print("Sorry integers don't have length")
    else:
        print("Sorry floats don't have length")
except:
    print(length(c))

The output results are as follows:

> enter a string: sfkelkrelte
11
> enter a string: 21
Sorry integers don't have length
> enter a string: 21.1
4

When I input an integer, the error message is displayed correctly, as the conversion float() is possible. But, in case of a floating point number, the interpreter goes to except block, though it should have executed the try block.

Why does this happen?

Upvotes: 1

Views: 17185

Answers (3)

pault
pault

Reputation: 43504

The part that is raising the exception is int(c):

c = "21.1"
print(int(c))
# ValueError: invalid literal for int() with base 10: '21.1'

One minor change would fix this for you:

c="21.1"

try:
    float(c)
    if "." not in c: #<---- check if "." is in the string c AFTER conversion to float
        print("Sorry integers don't have length")
    else:
        print("Sorry floats don't have length")
except:
    print(len(c))
# Sorry floats don't have length

However, it's generally bad practice to blindly catch all exceptions. This would have the unintended side effect of any error in your program triggering the except block.

It would be more appropriate to catch only the one you are expecting. 

c="21.aakdjs1"

try:
    float(c)
    if "." not in c:
        print("Sorry integers don't have length")
    else:
        print("Sorry floats don't have length")
except ValueError:
    print(len(c))
# 10

For future debugging, you can always print the exception.

Upvotes: 0

jose_bacoy
jose_bacoy

Reputation: 12684

Input results to a string format so convert the string into float Then check if it is an integer. Change your code into:

old: if float(c) ==int(c):

new: if c.isdigit():

UPDATED:

enter a string: 21.0
Sorry floats don't have length

Upvotes: 0

finefoot
finefoot

Reputation: 11232

Also, why not apply the EAFP principle (What is the EAFP principle in Python?) to the second condition, too?

s = input("Input: ")
try:
    float(s)
    try:
        int(s)
        print("Sorry, you have entered an integer.")
    except:
        print("Sorry, you have entered a float.")
except:
    print(len(s))

I have omitted to check for ValueError as the exception, because you didn't check that in your code, too. However, you should have a look at How to properly ignore exceptions

Upvotes: 1

Related Questions