Re: [Tutor] Stuck on some basics re floats
On 18/07/18 14:10, Matthew Polack wrote:
> Thanks for the reply Alan.
>
> I found another fix where I could just use this:
>
> num1 =int(input('Ener inches here?: '))
>
>
> but a lot of people like yourself seem to be recommending this
> 'float' method.
It all depends whether your input is a float or an integer.
If it will always be a whole number of inches then use int().
If it will be a floating point value then you need to use float().
In your example I'd have thought it reasonable to allow
conversions of, say, 11.5 inches...
I meant to add that its generally considered good practice
to do the conversion as early as possible unless you plan
on using the string version later. So wrapping the input()
call inside the int or float call is good.
You can then wrap that inside a try/except and get the user
to re-try if they type invalid data - if you so wish...
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
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Re: [Tutor] Stuck on some basics re floats
Matthew Polack writes:
> I'm a teacher trying to learn Python with my students.
Wonderful! Thank you for choosing Python for teaching your students.
> I am trying to make a very simple 'unit calculator' program...but I get an
> error ..I think python is treating my num1 variable as a text string...not
> an integer.
Yes. You are using the ‘input’ function, built in to Python 3
https://docs.python.org/3/library/functions.html#input>.
Read the documentation for that function; when successful, it returns
text (“a string”).
If you want an integer, you will need to explicitly tell Python to
convert the text to an integer value.
To create a new object, a general way is to use the type as a
constructor. The type you want is ‘int’, so use that as the constructor,
and you will (if it succeeds) get a new integer as the return value::
response = input("Enter inches here: ")
inches = int(response)
You will also need to learn about handling conversion errors: Try
entering something that is *not* a representation of an integer and see
what happens. How to handle the error is up to you.
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`\ the entire area was missing.” —Steven Wright |
_o__) |
Ben Finney
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Re: [Tutor] Stuck on some basics re floats
Matthew Polack wrote:
> Hi,
>
> I'm a teacher trying to learn Python with my students.
>
> I am trying to make a very simple 'unit calculator' program...but I get an
> error ..I think python is treating my num1 variable as a text string...not
> an integer.
>
> How do I fix this?
>
> Thanks!
>
> - Matt
>
> print ("How many inches would you like to convert? ")
> num1 = input('Enter inches here')
As you have guessed, at this point num1 is a string. You can convert it to a
float with
num1 = float(num1)
> print ("You have entered",num1, "inches")
> convert = num1 * 2.54
> print ("This is", convert, "centimetres")
>
>
> Traceback (most recent call last):
> File "convert.py", line 10, in
> convert = num1 * 2.54
> TypeError: can't multiply sequence by non-int of type 'float'
Note that int is mentioned here because Python can multiply int with str,
though the result might surprise you:
>>> "spam" * 3
'spamspamspam'
So * also works as the repetition-operator just like + is also used to
concat strings.
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Re: [Tutor] Stuck on some basics re floats
On 18/07/18 00:52, Matthew Polack wrote:
> Hi,
>
> I'm a teacher trying to learn Python with my students.
>
> I am trying to make a very simple 'unit calculator' program...but I get an
> error ..I think python is treating my num1 variable as a text string...not
> an integer.
You are correct.
> How do I fix this?
Convert the string to a float:
f = float(s)
> print ("How many inches would you like to convert? ")
> num1 = input('Enter inches here')
In Python 3 input() always returns a string.
In python 2 input() returns an evaluated version of the
string, so if a number was entered Python returned a number.
This was a serious security risk however, so input() was
removed in Python 3 and the old raw_input() was
renamed as input().
> print ("You have entered",num1, "inches")
> convert = num1 * 2.54
convert = float(num1) * 2.54
> print ("This is", convert, "centimetres")
HTH
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos
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[Tutor] Stuck on some basics re floats
Hi,
I'm a teacher trying to learn Python with my students.
I am trying to make a very simple 'unit calculator' program...but I get an
error ..I think python is treating my num1 variable as a text string...not
an integer.
How do I fix this?
Thanks!
- Matt
print ("How many inches would you like to convert? ")
num1 = input('Enter inches here')
print ("You have entered",num1, "inches")
convert = num1 * 2.54
print ("This is", convert, "centimetres")
Traceback (most recent call last):
File "convert.py", line 10, in
convert = num1 * 2.54
TypeError: can't multiply sequence by non-int of type 'float'
Matthew Polack | Teacher
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