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Python Comparison Solution

Lorrian Landicho
Lorrian Landicho
278 Points

Coercing integer

As part of the FizzBuzz name = input("Please enter your name: ") number = input("Please enter a number: ")

TODO: Make sure the number is an integer

number = int(number)

treehouse:~/workspace$ python challenge.py
Please enter your name: Sam
Please enter a number: 4.5
Traceback (most recent call last):
File "challenge.py", line 5, in <module>
number = int(number)
ValueError: invalid literal for int() with base 10: '4.5'

Why did the coercion to integer not work?

Mike D
Mike D
2,792 Points

4.5 is a float not an integer. So, it throws a ValueError exception because it's expecting an integer, but receiving a float instead.

If the goal is to only accept integers, consider using a try/except block, so it forces the user input to only accept int's and not break when undesired input is entered.

2 Answers

Kent Åsvang
Kent Åsvang
18,823 Points

The built-in function input() returns the input as a string. Trying to convert the string '4.5' to an integer won't work, but you can turn it into a float():

    number = input("Enter a number ")  # Take a number from the user
    number = float(number)                    # Convert it to a float

A float can in turn be converted into an int, but remember that this will trim away all the decimals. int(4.5) -> 4

    number = '4.5'         # prints '4.5'
    float(number)         # prints 4.5
    int(float(number))  # prints 4

Hope this helped.

Lorrian Landicho
Lorrian Landicho
278 Points

The entered value 4.5 was a string, correct? And that is the reason I was coercing it to an integer.

number = "4.5" number=int(float(number))

Why is the string 4.5 can be coerced to a float, and not to integer?

Kent Åsvang
Kent Åsvang
18,823 Points

If you call int() on a string decimal like '4.5', you are implicitly calling a float() first, which is not the pythonic way. Python is aiming to be a literal and readable language, therefore int() can only coerce a string('4') or a float('45.5').

Be aware of the fact that the int() function doesn't round the float you are passing to it, it just truncates it - removes everything after the decimal point.

The solution I came up with to this problem was to coerce the input string into a float, round the float, and coerce the float to an integer. This allowed for accurate rounding to the nearest integer.

number = int(round(float(number)))